Historic Mass Masonry Restoration Discussion

AE 537 – Visiting Practitioner Lecture: 

Historic Mass Masonry Restoration and Case Study:  Erik Valentino, MPS

Reading for Discussion and Future Reference on the topic of Historic Masonry Repair and Restoration:

 

TECHNICAL NOTES on Brick Construction 46:  Maintainence of Brick Masonry – December 2005

Abstract: Even though one of the major advantages of brick masonry construction is durability, periodic inspections and maintenance can extend the life of brickwork in structures. This Technical Note discusses the benefits and elements of suggested inspection programs and describes specific maintenance procedures including replacement of sealant joints, grouting of mortar joint faces, repointing of mortar joints, removal of plant growth, repair of weeps, replacement of brick, installation of a dampproof course, installation of flashing in existing walls and replacement of wall ties.

Key Words:  anchors, cleaning, dampproof course, efflorescence, flashing, inpsection, maintenance, moisture penetration, mortar, repointing, sealant, ties, weeps.

SUMMARY OF RECOMMENDATIONS:

• Perform periodic inspections, preferably each season

• Determine moisture source before attempting repairs to correct moisture penetration

• Remove and replace torn, deteriorated or inelastic sealants

• When repairing mortar joints, surface grout hairline cracks and repoint damaged or deteriorating mortar joints

• Repoint with prehydrated Type N, O or K mortar, mixed drier than for conventional masonry work

• Remove ivy and plant growth that contributes to moisture penetration or deterioration of brickwork

• Exercise care in opening existing or drilling new weeps, to ensure that flashing is not damaged

• Install a dampproof course if missing or required

• Install remedial anchors and ties in accordance with manufacturer’s recommendations

• Inspect masonry and correct all deficiencies before application of external coatings 

Download Full Version of BIA Tech Note 46 NOW 

Preservation Brief 2:  Repointing Mortar Joints in Historic Masonry Buidlings – National Park Service

This document is produced by the US National Park Service and as such is in the public domain.  It has been reproduced in its entirety below for your convenience:

2   Technical Preservation Services, HPS, masthead; link to ParkNet

 

 

Home page logo: Soft mortar being used for repointing. Photo: John P. Speweik.

 

Repointing Mortar Joints in
Historic Masonry Buildings

Robert C. Mack, FAIA, and John P. Speweik»Historical Background
Identifying the Problem Before Repointing
»Finding an Appropriate Mortar Match
»Properties of Mortar
»Mortar Analysis
»Components of Mortar
»Mortar Type and Mix
»Budgeting and Scheduling
»Contractor Selection
»Execution of the Work
»Visually Examining the Mortar and the Masonry Units
»Summary
»Conclusion
»Selected Reading

A NOTE TO OUR — USERS: The web versions of the Preservation Briefs differ somewhat from the printed versions. Many illustrations are new, captions are simplified, illustrations are typically in color rather than black and white, and some complex charts have been omitted. 

 

Masonry–brick, stone, terra-cotta, and concrete block–is found on nearly every historic building.Structures with all-masonry exteriors come to mind immediately, but most other buildings at least have masonry foundations or chimneys. Although generally considered “permanent,” masonry is subject to deterioration, especially at the mortar joints. Repointing, also known simply as “pointing”or–somewhat inaccurately–“tuck pointing”*, is the process of removing deteriorated mortar from the joints of a masonry wall and replacing it with new mortar. Properly done, repointing restores the visual and physical integrity of the masonry. Improperly done, repointing not only detracts from the appearance of the building, but may also cause physical damage to the masonry units themselves.

The purpose of this Brief is to provide general guidance on appropriate materials and methods for repointing historic masonry buildings and it is intended to benefit building owners, architects, and contractors. The Brief should serve as a guide to prepare specifications for repointing historic masonry buildings. It should also help develop sensitivity to the particular needs of historic masonry, and to assist historic building owners in working cooperatively with architects, architectural conservators and historic preservation consultants, and contractors. Although specifically intended for historic buildings, the guidance is appropriate for other masonry buildings as well. This publication updates Preservation Briefs 2: Repointing Mortar Joints in Historic Brick Buildingsto include all types of historic unit masonry. The scope of the earlier Brief has also been expanded to acknowledge that the many buildings constructed in the first half of the 20th century are now historic and eligible for listing in the National Register of Historic Places, and that they may have been originally constructed with portland cement mortar.

*Tuckpointing technically describes a primarily decorative application of a raised mortar joint or lime putty joint on top of flush mortar joints.


Historical Background

Mortar consisting primarily of lime and sand has been used as an integral part of masonry structures for thousands of years. Up until about the mid-19th century, lime or quicklime (sometimes called lump lime) was delivered to construction sites, where it had to be slaked, or combined with water. Mixing with water caused it to boil and resulted in a wet lime putty that was left to mature in a pit or wooden box for several weeks, up to a year. Traditional mortar was made from lime putty, or slaked lime, combined with local sand, generally in a ratio of 1 part lime putty to 3 parts sand by volume. Often other ingredients, such as crushed marine shells (another source of lime), brick dust, clay, natural cements, pigments, and even animal hair were also added to mortar, but the basic formulation for lime putty and sand mortar remained unchanged for centuries until the advent of portland cement or its forerunner, Roman cement, a natural, hydraulic cement.

Portland cementwas patented in Great Britain in 1824. It was named after the stone from Portland in Dorset which it resembled when hard. This is a fast-curing, hydraulic cement which hardens under water. Portland cement was first manufactured in the United States in 1872, although it was imported before this date. But it was not in common use throughout the country until the early 20th century. Up until the turn of the century portland cement was considered primarily an additive, or “minor ingredient” to help accelerate mortar set time. By the 1930s, however, most masons used a mix of equal parts portland cement and lime putty. Thus, the mortar found in masonry structures built between 1873 and 1930 can range from pure lime and sand mixes to a wide variety of lime, portland cement, and sand combinations.

In the 1930s more new mortar products intended to hasten and simplify masons’ work were introduced in the U.S. These included masonry cement, a premixed, bagged mortar which is a combination of portland cement and ground limestone, and hydrated lime, machine-slaked lime that eliminated the necessity of slaking quicklime into putty at the site.


Identifying the Problem Before Repointing

The decision to repoint is most often related to some obvious sign of deterioration, such as disintegrating mortar, cracks in mortar joints, loose bricks or stones, damp walls, or damaged plasterwork. It is, however, erroneous to assume that repointing alone will solve deficiencies that result from other problems. The root cause of the deterioration–leaking roofs or gutters, differential settlement of the building, capillary action causing rising damp, or extreme weather exposure–should always be dealt with prior to beginning work.

masons applying lime putty mortar
Masons practice using lime putty mortar to repair historic marble. Photo: NPS files.

Without appropriate repairs to eliminate the source of the problem, mortar deterioration will continue and any repointing will have been a waste of time and money.

Use of Consultants.Because there are so many possible causes for deterioration in historic buildings, it may be desirable to retain a consultant, such as a historic architect or architectural conservator, to analyze the building. In addition to determining the most appropriate solutions to the problems, a consultant can prepare specifications which reflect the particular requirements of each job and can provide oversight of the work in progress. Referrals to preservation consultants frequently can be obtained from State Historic Preservation Offices, the American Institute for Conservation of Historic and Artistic Works (AIC), the Association for Preservation Technology (APT), and local chapters of the American Institute of Architects (AIA).


Finding an Appropriate Mortar Match

Preliminary research is necessary to ensure that the proposed repointing work is both physically and visually appropriate to the building. Analysis of unweathered portions of the historic mortar to which the new mortar will be matched can suggest appropriate mixes for the repointing mortar so that it will not damage the building because it is excessively strong or vapor impermeable.

repointed 19th c. granite
This late 19th century granite has recently been repointed with the joint profile and mortar color carefully matched to the original. Photo: NPS files.

Examination and analysis of the masonry units–brick, stone or terra cotta–and the techniques used in the original construction will assist in maintaining the building’s historic appearance. A simple, non- technical, evaluation of the masonry units and mortar can provide information concerning the relative strength and permeability of each–critical factors in selecting the repointing mortar–while a visual analysis of the historic mortar can provide the information necessary for developing the new mortar mix and application techniques.

Although not crucial to a successful repointing project, for projects involving properties of special historic significance, a mortar analysis by a qualified laboratory can be useful by providing information on the original ingredients. However, there are limitations with such an analysis, and replacement mortar specifications should not be based solely on laboratory analysis. Analysis requires interpretation, and there are important factors which affect the condition and performance of the mortar that cannot be established through laboratory analysis. These may include: the original water content, rate of curing, weather conditions during original construction, the method of mixing and placing the mortar, and the cleanliness and condition of the sand. The most useful information that can come out of laboratory analysis is the identification of sand by gradation and color.This allows the color and the texture of the mortar to be matched with some accuracy because sand is the largest ingredient by volume.

In creating a repointing mortar that is compatible with the masonry units, the objective is to achieve one that matches the historic mortar as closely as possible, so that the new material can coexist with the old in a sympathetic, supportive and, if necessary, sacrificial capacity. The exact physical and chemical properties of the historic mortar are not of major significance as long as the new mortar conforms to the following criteria:

  • The new mortar must match the historic mortar in color, texture and tooling. (If a laboratory analysis is undertaken, it may be possible to match the binder components and their proportions with the historic mortar, if those materials are available.) 
  • The sand must match the sandin the historic mortar. (The color and texture of the new mortar will usually fall into place if the sand is matched successfully.) 
  • The new mortar must have greater vapor permeability and be softer (measured in compressive strength) than the masonry units. 
  • The new mortar must be as vapor permeable and as soft or softer (measured in compressive strength) than the historic mortar. (Softness or hardness is not necessarily an indication of permeability; old, hard lime mortars can still retain high permeability.) 

 

mortar with proper consistency
This mortar is the proper consistency for repointing historic brick. Photo: John P. Speweik.

 

Mortar Analysis

Methods for analyzing mortars can be divided into two broad categories: wet chemical and instrumental. Many laboratories that analyze historic mortars use a simple wet-chemical method called acid digestion, whereby a sample of the mortar is crushed and then mixed with a dilute acid. The acid dissolves all the carbonate-containing minerals not only in the binder, but also in the aggregate (such as oyster shells, coral sands, or other carbonate-based materials), as well as any other acid-soluble materials. The sand and fine-grained acid-insoluble material is left behind. There are several variations on the simple acid digestion test. One involves collecting the carbon dioxide gas given off as the carbonate is digested by the acid; based on the gas volume the carbnate content of the mortar can be accurately determined (Jedrzejewska, 1960). Simple acid digestion methods are rapid, inexpensive, and easy to perform, but the information they provide about the original composition of a mortar is limited to the color and texture of the sand. The gas collection method provides more information about the binder than a simple acid digestion test.

Instrumental analysis methods that have been used to evaluate mortars include polarized light or thin-section microscopy, scanning electron microscopy, atomic absorption spectroscopy, X-ray diffraction, and differential thermal analysis. All instrumental methods require not only expensive, specialized equipment, but also highly-trained experienced analysts. However, instrumental methods can provide much more information about a mortar. Thin-section microscopy is probably the most commonly used instrumental method. Examination of thin slices of a mortar in transmitted light is often used to supplement acid digestion methods, particularly to look for carbonate-based aggregate. For example, the new ASTM test method, ASTM C 1324-96 “Test Method for Examination and Analysis of Hardened Mortars” which was designed specifically for the analysis of modern lime-cement and masonry cement mortars, combines a complex series of wet chemical analyses with thin-section microscopy.

The drawback of most mortar analysis methods is that mortar samples of known composition have not been analyzed in order to evaluate the method. Historic mortars were not prepared to narrowly defined specifications from materials of uniform quality; they contain a wide array of locally derived materials combined at the discretion of the mason. While a particular method might be able to accurately determine the original proportions of a lime-cement-sand mortar prepared from modern materials, the usefulness of that method for evaluating historic mortars is questionable unless it has been tested against mortars prepared from materials more commonly used in the past. Lorraine Schnabel.


Properties of Mortar

 

Mortars for repointing should be softer or more permeable than the masonry units and no harder or more impermeable than the historic mortar to prevent damage to the masonry units. It is a common error to assume that hardness or high strength is a measure of appropriateness, particularly for lime-based historic mortars. Stresses within a wall caused by expansion, contraction, moisture migration, or settlement must be accommodated in some manner; in a masonry wall, these stresses should be relieved by the mortar rather than by the masonry units. A mortar that is stronger in compressive strength than the masonry units will not “give,” thus causing stresses to be relieved through the masonry units–resulting in permanent damage to the masonry, such as cracking and spalling, that cannot be repaired easily.

repointing of 19th c. building with lime mortar
This early 19th century building is being repointed with lime mortar. Photo: Travis McDonald.

 

While stresses can also break the bond between the mortar and the masonry units, permitting water to penetrate the resulting hairline cracks, this is easier to correct in the joint through repointing than if the break occurs in the masonry units.

Permeability, or rate of vapor transmission, is also critical. High lime mortars are more permeable than denser cement mortars. Historically, mortar acted as a bedding material–not unlike an expansion joint–rather than a “glue” for the masonry units, and moisture was able to migrate through the mortar joints rather than the masonry units. When moisture evaporates from the masonry it deposits any soluble salts either on the surface as efflorescence or below the surface as subflorescence.While salts deposited on the surface of masonry units are usually relatively harmless, salt crystallization within a masonry unit creates pressure that can cause parts ofthe outer surface to spall off or delaminate. If the mortar does not permitmoisture or moisture vapor to migrate out of the wall and evaporate, theresult will be damage to the masonry units.


Components of Mortar

Sand.Sand is the largest component of mortar and the material that gives mortar its distinctive color, texture and cohesiveness. Sand must be free of impurities, such as salts or clay. The three key characteristics of sand are: particle shape, gradation and void ratios.

When viewed under a magnifying glass or low-power microscope, particles of sand generally have either rounded edges, such as found in beach and river sand, or sharp, angular edges, found in crushed or manufactured sand. For repointing mortar, rounded or natural sand is preferred for two reasons. It is usually similar to the sand in the historic mortar and provides a better visual match. It also has better working qualities or plasticity and can thus be forced into the joint more easily, forming a good contact with the remaining historic mortar and the surface of the adjacent masonry units. Although manufactured sand is frequently more readily available, it is usually possible to locate a supply of rounded sand.

The gradation of the sand (particle size distribution) plays a very important role in the durability and cohesive properties of a mortar. Mortar must have a certain percentage of large to small particle sizes in order to deliver the optimum performance. Acceptable guidelines on particle size distribution may be found in ASTM C 144 (American Society for Testing and Materials). However, in actuality, since neither historic nor modern sands are always in compliance with ASTM C 144, matching the same particle appearance and gradation usually requires sieving the sand.

A scoop of sand contains many small voids between the individual grains. A mortar that performs well fills all these small voids with binder (cement/lime combination or mix) in a balanced manner. Well-graded sand generally has a 30 per cent void ratio by volume. Thus, 30 per cent binder by volume generally should be used, unless the historic mortar had a different binder: aggregate ratio. This represents the 1:3 binder to sand ratios often seen in mortar specifications.

For repointing, sand generally should conform to ASTM C 144 to assure proper gradation and freedom from impurities; some variation may be necessary to match the original size and gradation. Sand color and texture also should match the original as closely as possible to provide the proper color match without other additives.

Lime.Mortar formulations prior to the late-19th century used lime as the primary binding material. Lime is derived from heating limestone at high temperatures which burns off the carbon dioxide, and turns the limestone into quicklime. There are three types of limestone–calcium, magnesium, and dolomitic–differentiated by the different levels of magnesium carbonate they contain which impart specific qualities to mortar. Historically, calcium lime was used for mortar rather than the dolomitic lime (calcium magnesium carbonate) most often used today. But it is also important to keep in mind the fact that the historic limes, and other components of mortar, varied a great deal because they were natural, as opposed to modern lime which is manufactured and, therefore, standardized. Because some of the kinds of lime, as well as other components of mortar, that were used historically are no longer readily available, even when a conscious effort is made to replicate a “historic” mix, this may not be achievable due to the differences between modern and historic materials.

inappropriate caulking on the top of wall
Caulking was inappropriately used here in place of mortar on the top of the wall. As a result, it has not been durable. Photo: NPS files.

Lime, itself, when mixed with water into a paste is very plastic and creamy. It will remain workable and soft indefinitely, if stored in a sealed container. Lime (calcium hydroxide) hardens by carbonation absorbing carbon dioxide primarily from the air, converting itself to calcium carbonate. Once a lime and sand mortar is mixed and placed in a wall, it begins the process of carbonation. If lime mortar is left to dry too rapidly, carbonation of the mortar will be reduced, resulting in poor adhesion and poor durability. In addition, lime mortar is slightly water soluble and thus is able to re-seal any hairline cracks that may develop during the life of the mortar. Lime mortar is soft, porous, and changes little in volume during temperature fluctuations thus making it a good choice for historic buildings. Because of these qualities, high calcium lime mortar may be considered for many repointing projects, not just those involving historic buildings.

For repointing, lime should conform to ASTM C 207, Type S, or Type SA, Hydrated Lime for Masonry Purposes. This machine-slaked lime is designed to assure high plasticity and water retention. The use of quicklime which must be slaked and soaked by hand may have advantages over hydrated lime in some restoration projects if time and money allow.

Lime putty.Lime putty is slaked lime that has a putty or paste-like consistency. It should conform to ASTM C 5. Mortar can be mixed using lime putty according to ASTM C 270 property or proportion specification.

Portland cement. More recent, 20th-century mortar has used portland cement as a primary binding material. A straight portland cement and sand mortar is extremely hard, resists the movement of water, shrinks upon setting, and undergoes relatively large thermal movements. When mixed with water, portland cement forms a harsh, stiff paste that is quite unworkable, becoming hard very quickly. (Unlike lime, portland cement will harden regardless of weather conditions and does not require wetting and drying cycles.) Some portland cement assists the workability and plasticity of the mortar without adversely affecting the finished project; it also provides early strength to the mortar and speeds setting. Thus, it may be appropriate to add some portland cement to an essentially lime-based mortar even when repointing relatively soft 18th or 19th century brick under some circumstances when a slightly harder mortar is required. The more portland cement that is added to a mortar formulation the harder it becomes–and the faster the initial set.

For repointing, portland cement should conform to ASTM C 150. White, non- staining portland cement may provide a better color match for some historic mortars than the more commonly available grey portland cement. But, it should not be assumed, however, that white portland cement is always appropriate for all historic buildings, since the original mortar may have been mixed with grey cement. The cement should not have more than 0.60 per cent alkali to help avoid efflorescence.

Masonry cement. Masonry cement is a preblended mortar mix commonly found at hardware and home repair stores. It is designed to produce mortars with a compressive strength of 750 psi or higher when mixed with sand and water at the job site. It may contain hydrated lime, but it always contains a large amount of portland cement, as well as ground limestone and other workability agents, including air-entraining agents. Because masonry cements are not required to contain hydrated lime, and generally do not contain lime, they produce high strength mortars that can damage historic masonry. For this reason, they generally are not recommended for use on historic masonry buildings.

Lime mortar (pre-blended). Hydrated lime mortars, and pre-blended lime putty mortars with or without a matched sand are commercially available. Custom mortars are also available with color. In most instances, pre-blended lime mortars containing sand may not provide an exact match; however, if the project calls for total repointing, a pre-blended lime mortar may be worth considering as long as the mortar is compatible in strength with the masonry. If the project involves only selected, “spot” repointing, then it may be better to carry out a mortar analysis which can provide a custom pre-blended lime mortar with a matching sand. In either case, if a preblended lime mortar is to be used, it should contain Type S or SA hydrated lime conforming to ASTM C 207.

Water. Water should be potable–clean and free from acids, alkalis, or other dissolved organic materials.

Other Components

Historic components.In addition to the color of the sand, the texture of the mortar is of critical importance in duplicating historic mortar. Most mortars dating from the mid-19th century on–with some exceptions–have a fairly homogeneous texture and color. Some earlier mortars are not as uniformly textured and may contain lumps of partially burned lime or “dirty lime”, shell (which often provided a source of lime, particularly in coastal areas), natural cements, pieces of clay, lampblack or other pigments, or even animal hair. The visual characteristics of these mortars can be duplicated through the use of similar materials in the repointing mortar.

Replicating such unique or individual mortars will require writing new specifications for each project. If possible, suggested sources for special materials should be included. For example, crushed oyster shells can be obtained in a variety of sizes from poultry supply dealers.

Pigments.Some historic mortars, particularly in the late 19th century, were tinted to match or contrast with the brick or stone. Red pigments, sometimes in the form of brick dust, as well as brown, and black pigments were commonly used. Modern pigments are available which can be added to the mortar at the job site, but they should not exceed 10 per cent by weight of the portland cement in the mix, and carbon black should be limited to 2 per cent. Only synthetic mineral oxides, which are alkali-proof and sun-fast, should be used to prevent bleaching and fading.

Modern components. Admixtures are used to create specific characteristics in mortar, and whether they should be used will depend upon the individual project. Air entraining agents, for example, help the mortar to resist freeze-thaw damage in northern climates. Accelerators are used to reduce mortar freezing prior to setting while retardershelp to extend the mortar life in hot climates. Selection of admixtures should be made by the architect or architectural conservator as part of the specifications, not something routinely added by the masons.

Generally, modern chemical additives are unnecessary and may, in fact, have detrimental effects in historic masonry projects. The use of antifreeze compounds is not recommended. They are not very effective with high lime mortars and may introduce salts, which may cause efflorescence later. A better practice is to warm the sand and water, and to protect the completed work from freezing. No definitive study has determined whether air-entraining additives should be used to resist frost action and enhance plasticity, but in areas of extreme exposure requiring high-strength mortars with lower permeability, air-entrainment of 10-16 percent may be desirable (see formula for “severe weather exposure” in Mortar Type and Mix). Bonding agents are not a substitute for proper joint preparation, and they should generally be avoided. If the joint is properly prepared, there will be a good bond between the new mortar and the adjacent surfaces. In addition, a bonding agent is difficult to remove if smeared on a masonry surface.

Mortar Type and Mix

Mortars for repointing projects, especially those involving historic buildings, typically are custom mixed in order to ensure the proper physical and visual qualities. These materials can be combined in varying proportions to create a mortar with the desired performance and durability. The actual specification of a particular mortar type should take into consideration all of the factors affecting the life of the building including: current site conditions, present condition of the masonry, function of the new mortar, degree of weather exposure, and skill of the mason.

appropriate preparation for repointing
Here, a hammer and chisel are being correctly used to prepare a joint for repointing. Photo: John P. Speweik.

Thus, no two repointing projects are exactly the same. Modern materials specified for use in repointing mortar should conform to specifications of the American Society for Testing and Materials (ASTM) or comparable federal specifications, and the resulting mortar should conform to ASTM C 270, Mortar for Unit Masonry.

Specifying the proportions for the repointing mortar for a specific job is not as difficult as it might seem. Five mortar types, each with a corresponding recommended mix, have been established by ASTM to distinguish high strength mortar from soft flexible mortars. The ASTM designated them in decreasing order of approximate general strength as Type M (2,500 psi), Type S (1,800 psi), Type N (750 psi), Type O (350 psi) and Type K (75 psi). (The letters identifying the types are from the words MASON WORK using every other letter.) Type K has the highest lime content of the mixes that contain portland cement, although it is seldom used today, except for some historic preservation projects. The designation “L” in the accompanying chart identifies a straight lime and sand mix. Specifying the appropriate ASTM mortar by proportion of ingredients, will ensure the desired physical properties. Unless specified otherwise, measurements or proportions for mortar mixes are always given in the following order: cement-lime-sand. Thus, a Type K mix, for example, would be referred to as 1-3-10, or 1 part cement to 3 parts lime to 10 parts sand. Other requirements to create the desired visual qualities should be included in the specifications.

The strength of a mortar can vary. If mixed with higher amounts of portland cement, a harder mortar is obtained. The more lime that is added, the softer and more plastic the mortar becomes, increasing its workability. A mortar strong in compressive strength might be desirable for a hard stone (such as granite) pier holding up a bridge deck, whereas a softer, more permeable lime mortar would be preferable for a historic wall of soft brick. Masonry deterioration caused by salt deposition results when the mortar is less permeable than the masonry unit. A strong mortar is still more permeable than hard, dense stone. However, in a wall constructed of soft bricks where the masonry unit itself has a relatively high permeability or vapor transmission rate, a soft, high lime mortar is necessary to retain sufficient permeability.


Budgeting and Scheduling

Repointing is both expensive and time consuming due to the extent of handwork and special materials required. It is preferable to repoint only those areas that require work rather than an entire wall, as is often specified. But, if 25 to 50 per cent or more of a wall needs to be repointed, repointing the entire wall may be more cost effective than spot repointing.

profile raised during repointing
When repairing this stone wall, the mason matched the raised profile of the original tuckpointing. Photo: NPS files.

Total repointing may also be more sensible when access is difficult, requiring the erection of expensive scaffolding (unless the majority of the mortar is sound and unlikely to require replacement in the foreseeable future). Each project requires judgement based on a variety of factors. Recognizing this at the outset will help to prevent many jobs from becoming prohibitively expensive.

In scheduling, seasonal aspects need to be considered first. Generally speaking, wall temperatures between 40 and 95 degrees F (8 and 38 degrees C) will prevent freezing or excessive evaporation of the water in the mortar. Ideally, repointing should be done in shade, away from strong sunlight in order to slow the drying process, especially during hot weather. If necessary, shade can be provided for large-scale projects with appropriate modifications to scaffolding.

The relationship of repointing to other work proposed on the building must also be recognized. For example, if paint removal or cleaning is anticipated, and if the mortar joints are basically sound and need only selective repointing, it is generally better to postpone repointing until after completion of these activities. However, if the mortar has eroded badly, allowing moisture to penetrate deeply into the wall, repointing should be accomplished before cleaning. Related work, such as structural or roof repairs, should be scheduled so that they do not interfere with repointing and so that all work can take maximum advantage of erected scaffolding.

Building managers also must recognize the difficulties that a repointing project can create.

damage caused by mechanical grinder
A mechanical grinder improperly used to cut out the horizontal joint and incompatible repointing have seriously damaged the 19th century brick. Photo: NPS files.

The process is time consuming, and scaffolding may need to remain in place for an extended period of time. The joint preparation process can be quite noisy and can generate large quantities of dust which must be controlled, especially at air intakes to protect human health, and also where it might damage operating machinery. Entrances may be blocked from time to time making access difficult for both building tenants and visitors. Clearly, building managers will need to coordinate the repointing work with other events at the site.

Contractor Selection

The ideal way to select a contractor is to ask knowledgeable owners of recently repointed historic buildings for recommendations. Qualified contractors then can provide lists of other repointing projects for inspection. More commonly, however, the contractor for a repointing project is selected through a competitive bidding process over which the client or consultant has only limited control. In this situation it is important to ensure that the specifications stipulate that masons must have a minimum of five years’ experience with repointing historic masonry buildings to be eligible to bid on the project. Contracts are awarded to the lowest responsible bidder, and bidders who have performed poorly on other projects usually can be eliminated from consideration on this basis, even if they have the lowest prices.

The contract documents should call for unit prices as well as a base bid. Unit pricing forces the contractor to determine in advance what the cost addition or reduction will be for work which varies from the scope of the base bid. If, for example, the contractor has fifty linear feet less of stone repointing than indicated on the contract documents but thirty linear feet more of brick repointing, it will be easy to determine the final price for the work. Note that each type of work–brick repointing, stone repointing, or similar items–will have its own unit price. The unit price also should reflect quantities; one linear foot of pointing in five different spots will be more expensive than five contiguous linear feet.

Execution of the Work

Test Panels. These panels are prepared by the contractor using the same techniques that will be used on the remainder of the project. Several panel locations–preferably not on the front or other highly visible location of the building–may be necessary to include all types of masonry, joint styles, mortar colors, and other problems likely to be encountered on the job.

inappropriate repointing causing loss of character
Unskilled repointing has negatively impacted the character of this late-19th century building. Photo: NPS files.

If cleaning tests, for example, are also to be undertaken, they should be carried out in the same location. Usually a 3 foot by 3 foot area is sufficient for brickwork, while a somewhat larger area may be required for stonework. These panels establish an acceptable standard of work and serve as a benchmark for evaluating and accepting subsequent work on the building.

Joint Preparation. Old mortar should be removed to a minimum depth of 2 to 2-1/2 times the width of the joint to ensure an adequate bond and to prevent mortar “popouts.” For most brick joints, this will require removal of the mortar to a depth of approximately ½ to 1 inch; for stone masonry with wide joints, mortar may need to be removed to a depth of several inches. Any loose or disintegrated mortar beyond this minimum depth also should be removed.

Although some damage may be inevitable, careful joint preparation can help limit damage to masonry units. The traditional manner of removing old mortar is through the use of hand chisels and mash hammers. Though labor-intensive, in most instances this method poses the least threat for damage to historic masonry units and produces the best final product.

The most common method of removing mortar, however, is through the use of power saws or grinders. The use of power tools by unskilled masons can be disastrous for historic masonry, particularly soft brick. Using power saws on walls with thin joints, such as most brick walls, almost always will result in damage to the masonry units by breaking the edges and by overcutting on the head, or vertical joints.

However, small pneumatically-powered chisels generally can be used safely and effectively to remove mortar on historic buildings as long as the masons maintain appropriate control over the equipment. Under certain circumstances, thin diamond-bladed grinders may be used to cut out horizontaljoints only on hard portland cement mortar common to most early-20th century masonry buildings. Usually, automatic tools most successfully remove old mortar without damaging the masonry units when they are used in combination with hand tools in preparation for repointing. Where horizontal joints are uniform and fairly wide, it may be possible to use a power masonry saw to assist the removal of mortar, such as by cutting along the middle of the joint; final mortar removal from the sides of the joints still should be done with a hand chisel and hammer. Caulking cutters with diamond blades can sometimes be used successfully to cut out joints without damaging the masonry. Caulking cutters are slow; they do not rotate, but vibrate at very high speeds, thus minimizing the possibility of damage to masonry units. Although mechanical tools may be safely used in limited circumstances to cut out horizontal joints in preparation for repointing, they should never be used on vertical joints because of the danger of slipping and cutting into the brick above or below the vertical joint. Using power tools to remove mortar without damaging the surrounding masonry units also necessitates highly skilled masons experienced in working on historic masonry buildings. Contractors should demonstrate proficiency with power tools before their use is approved.

Using any of these power tools may also be more acceptable on hard stone, such as quartzite or granite, than on terra cotta with its glass-like glaze, or on soft brick or stone. The test panel should determine the acceptability of power tools. If power tools are to be permitted, the contractor should establish a quality control program to account for worker fatigue and similar variables.

Mortar should be removed cleanly from the masonry units, leaving square corners at the back of the cut. Before filling, the joints should be rinsed with a jet of water to remove all loose particles and dust. At the time of filling, the joints should be damp, but with no standing water present. For masonry walls–limestone, sandstone and common brick–that are extremely absorbent, it is recommended that a continual mist of water be applied for a few hours before repointing begins.

Mortar Preparation.Mortar components should be measured and mixed carefully to assure the uniformity of visual and physical characteristics. Dry ingredients are measured by volume and thoroughly mixed before the addition of any water. Sand must be added in a damp, loose condition to avoid over sanding. Repointing mortar is typically pre-hydrated by adding water so it will just hold together, thus allowing it to stand for a period of time before the final water is added. Half the water should be added, followed by mixing for approximately 5 minutes. The remaining water should then be added in small portions until a mortar of the desired consistency is reached. The total volume of water necessary may vary from batch to batch, depending on weather conditions. It is important to keep the water to a minimum for two reasons: first, a drier mortar is cleaner to work with, and it can be compacted tightly into the joints; second, with no excess water to evaporate, the mortar cures without shrinkage cracks. Mortar should be used within approximately 30 minutes of final mixing, and “retempering,” or adding more water, should not be permitted.

Using Lime Putty to Make Mortar.Mortar made with lime putty and sand, sometimes referred to as roughage or course stuff, should be measured by volume, and may require slightly different proportions from those used with hydrated lime. No additional water is usually needed to achieve a workable consistency because enough water is already contained in the putty. Sand is proportioned first, followed by the lime putty, then mixed for five minutes or until all the sand is thoroughly coated with the lime putty. But mixing, in the familiar sense of turning over with a hoe, sometimes may not be sufficient if the best possible performance is to be obtained from a lime putty mortar. Although the old practice of chopping, beating and ramming the mortar has largely been forgotten, recent field work has confirmed that lime putty and sand rammed and beaten with a wooden mallet or ax handle, interspersed by chopping with a hoe, can significantly improve workability and performance. The intensity of this action increases the overall lime/sand contact and removes any surplus water by compacting the other ingredients. It may also be advantageous for larger projects to use a mortar pan mill for mixing. Mortar pan mills which have a long tradition in Europe produce a superior lime putty mortar not attainable with today’s modern paddle and drum type mixers.

For larger repointing projects the lime putty and sand can be mixed together ahead of time and stored indefinitely, on or off site, which eliminates the need for piles of sand on the job site. This mixture, which resembles damp brown sugar, must be protected from the air in sealed containers with a wet piece of burlap over the top or sealed in a large plastic bag to prevent evaporation and premature carbonation. The lime putty and sand mixture can be recombined into a workable plastic state months later with no additional water.

If portland cement is specified in a lime putty and sand mortar–Type O (1:2:9) or Type K (1:3:11)–the portland cement should first be mixed into a slurry paste before adding it to the lime putty and sand. Not only will this ensure that the portland cement is evenly distributed throughout the mixture, but if dry portland cement is added to wet ingredients it tends to “ball up,” jeopardizing dispersion. (Usually water must be added to the lime putty and sand anyway once the portland cement is introduced.) Any color pigments should be added at this stage and mixed for a full five minutes. The mortar should be used within 30 minutes to 1½ hours and it should not be retempered. Once portland cement has been added the mortar can no longer be stored.

Filling the Joint. Where existing mortar has been removed to a depth of greater than 1 inch, these deeper areas should be filled first, compacting the new mortar in several layers. The back of the entire joint should be filled successively by applying approximately 1/4 inch of mortar, packing it well into the back corners. This application may extend along the wall for several feet. As soon as the mortar has reached thumb-print hardness, another 1/4 inch layer of mortar–approximately the same thickness–may be applied. Several layers will be needed to fill the joint flush with the outer surface of the masonry. It is important to allow each layer time to harden before the next layer is applied; most of the mortar shrinkage occurs during the hardening process and layering thus minimizes overall shrinkage.

When the final layer of mortar is thumb-print hard, the joint should be tooled to match the historic joint. Proper timing of the tooling is important for uniform color and appearance. If tooled when too soft, the color will be lighter than expected, and hairline cracks may occur; if tooled when too hard, there may be dark streaks called “tool burning,” and good closure of the mortar against the masonry units will not be achieved.

If the old bricks or stones have worn, rounded edges, it is best to recess the final mortar slightly from the face of the masonry. This treatment will help avoid a joint which is visually wider than the actual joint; it also will avoid creation of a large, thin featheredge which is easily damaged, thus admitting water. After tooling, excess mortar can be removed from the edge of the joint by brushing with a natural bristle or nylon brush. Metal bristle brushes should never be used on historic masonry.

Curing Conditions. The preliminary hardening of high-lime content mortars–those mortars that contain more lime by volume than portland cement, i.e., Type O (1:2:9), Type K (1:3:11), and straight lime/sand, Type “L” (0:1:3)–takes place fairly rapidly as water in the mix is lost to the porous surface of the masonry and through evaporation. A high lime mortar (especially Type “L”) left to dry out too rapidly can result in chalking, poor adhesion, and poor durability. Periodic wetting of the repointed area after the mortar joints are thumb-print hard and have been finish tooled may significantly accelerate the carbonation process. When feasible, misting using a hand sprayer with a fine nozzle can be simple to do for a day or two after repointing. Local conditions will dictate the frequency of wetting, but initially it may be as often as every hour and gradually reduced to every three or four hours. Walls should be covered with burlap for the first three days after repointing. (Plastic may be used, but it should be tented out and not placed directly against the wall.) This helps keep the walls damp and protects them from direct sunlight. Once carbonation of the lime has begun, it will continue for many years and the lime will gain strength as it reverts back to calcium carbonate within the wall.


This 18th century pediment and surrounding wall exhibit distinctively different mortar joints. Photo: NPS files.

Aging the Mortar.Even with the best efforts at matching the existing mortar color, texture, and materials, there will usually be a visible difference between the old and new work, partly because the new mortar has been matched to the unweathered portions of the historic mortar. Another reason for a slight mismatch may be that the sand is more exposed in old mortar due to the slight erosion of the lime or cement. Although spot repointing is generally preferable and some color difference should be acceptable, if the difference between old and new mortar is too extreme, it may be advisable in some instances to repoint an entire area of a wall, or an entire feature such as a bay, to minimize the difference between the old and the new mortar. If the mortars have been properly matched, usually the best way to deal with surface color differences is to let the mortars age naturally. Other treatments to overcome these differences, including cleaning the non-repointed areas or staining the new mortar, should be carefully tested prior to implementation.

Staining the new mortar to achieve a better color match is generally not recommended, but it may be appropriate in some instances. Although staining may provide an initial match, the old and new mortars may weather at different rates, leading to visual differences after a few seasons. In addition, the mixtures used to stain the mortar may be harmful to the masonry; for example, they may introduce salts into the masonry which can lead to efflorescence.

Cleaning the Repointed Masonry. If repointing work is carefully executed, there will be little need for cleaning other than to remove the small amount of mortar from the edge of the joint following tooling. This can be done with a stiff natural bristle or nylon brush after the mortar has dried, but before it is initially set (1-2 hours). Mortar that has hardened can usually be removed with a wooden paddle or, if necessary, a chisel.

Further cleaning is best accomplished with plain water and natural bristle or nylon brushes. If chemicals must be used, they should be selected with extreme caution. Improper cleaning can lead to deterioration of the masonry units, deterioration of the mortar, mortar smear, and efflorescence. New mortar joints are especially susceptible to damage because they do not become fully cured for several months. Chemical cleaners, particularly acids, should never be used on dry masonry. The masonry should always be completely soaked once with water before chemicals are applied. After cleaning, the walls should be flushed again with plain water to remove all traces of the chemicals.

Several precautions should be taken if a freshly repointed masonry wall is to be cleaned. First, the mortar should be fully hardened before cleaning. Thirty days is usually sufficient, depending on weather and exposure; as mentioned previously, the mortar will continue to cure even after it has hardened. Test panels should be prepared to evaluate the effects of different cleaning methods. Generally, on newly repointed masonry walls, only very low pressure (100 psi) water washing supplemented by stiff natural bristle or nylon brushes should be used, except on glazed or polished surfaces, where only soft cloths should be used.**

New construction “bloom” or efflorescence occasionally appears within the first few months of repointing and usually disappears through the normal process of weathering. If the efflorescence is not removed by natural processes, the safest way to remove it is by dry brushing with stiff natural or nylon bristle brushes followed by wet brushing. Hydrochloric (muriatic) acid, is generally ineffective, and it should not be used to remove efflorescence. It may liberate additional salts, which, in turn, can lead to more efflorescence.

Surface Groutingis sometimes suggested as an alternative to repointing brick buildings, in particular. This process involves the application of a thin coat of cement-based grout to the mortar joints and the mortar/brick interface. To be effective, the grout must extend slightly onto the face of the masonry units, thus widening the joint visually. The change in the joint appearance can alter the historic character of the structure to an unacceptable degree. In addition, although masking of the bricks is intended to keep the grout off the remainder of the face of the bricks, some level of residue, called “veiling,” will inevitably remain. Surface grouting cannot substitute for the more extensive work of repointing, and it is not a recommended treatment for historic masonry.

**Additional information on masonry cleaning is presented in Preservation Briefs 1: Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings, Robert C. Mack, FAIA, and Anne Grimmer, Washington, D.C.: Technical Preservation Services, National Park Service, U.S. Department of the Interior, 2000; and Keeping it Clean: Removing Exterior Dirt, Paint, Stains & Graffiti from Historic Masonry Buildings, Anne E. Grimmer, Washington, D.C.: Technical Preservation Services, National Park Service, U.S. Department of the Interior, 1988.


Visually Examining the Mortar and the Masonry Units

A simple in situ comparison will help determine the hardness and condition of the mortar and the masonry units. Begin by scraping the mortar with a screwdriver, and gradually tapping harder with a cold chisel and mason’s hammer. Masonry units can be tested in the same way beginning, even more gently, by scraping with a fingernail. This relative analysis which is derived from the 10-point hardness scale used to describe minerals, provides a good starting point for selection of an appropriate mortar. It is described more fully in “The Russack System for Brick & Mortar Description” referenced in Selected Readingat the end of this Brief.

Mortar samples should be chosen carefully, and picked from a variety of locations on the building to find unweathered mortar, if possible. Portions of the building may have been repointed in the past while other areas may be subject to conditions causing unusual deterioration. There may be several colors of mortar dating from different construction periods or sand used from different sources during the initial construction. Any of these situations can give false readings to the visual or physical characteristics required for the new mortar. Variations should be noted which may require developing more than one mix.

1) Remove with a chisel and hammer three or four unweathered samples of the mortar to be matched from several locations on the building. (Set the largest sample aside–this will be used later for comparison with the repointing mortar). Removing a full representation of samples will allow selection of a “mean” or average mortar sample.

2) Mash the remaining samples with a wooden mallet, or hammer if necessary, until they are separated into their constituent parts. There should be a good handful of the material.

3) Examine the powdered portion–the lime and/or cement matrix of the mortar. Most particularly, note the color. There is a tendency to think of historic mortars as having white binders, but grey portland cement was available by the last quarter of the 19th century, and traditional limes were also sometimes grey. Thus, in some instances, the natural color of the historic binder may be grey, rather than white. The mortar may also have been tinted to create a colored mortar, and this color should be identified at this point.

4) Carefully blow away the powdery material (the lime and/or cement matrix which bound the mortar together).

5) With a low power (10 power) magnifying glass, examine the remaining sand and other materials such as lumps of lime or shell.

6) Note and record the wide range of color as well as the varying sizes of the individual grains of sand, impurities, or other materials.

Other Factors to Consider

Color. Regardless of the color of the binder or colored additives, the sand is the primary material that gives mortar its color. A surprising variety of colors of sand may be found in a single sample of historic mortar, and the different sizes of the grains of sand or other materials, such as incompletely ground lime or cement, play an important role in the texture of the repointing mortar. Therefore, when specifying sand for repointing mortar, it may be necessary to obtain sand from several sources and to combine or screen them in order to approximate the range of sand colors and grain sizes in the historic mortar sample.

Pointing Style. Close examination of the historic masonry wall and the techniques used in the original construction will assist in maintaining the visual qualities of the building. Pointing styles and the methods of producing them should be examined. It is important to look at both the horizontal and the vertical joints to determine the order in which they were tooled and whether they were the same style. Some late-19th and early-20th century buildings, for example, have horizontal joints that were raked back while the vertical joints were finished flush and stained to match the bricks, thus creating the illusion of horizontal bands. Pointing styles may also differ from one facade to another; front walls often received greater attention to mortar detailing than side and rear walls. Tuckpointing is not true repointing but the application of a raised joint or lime putty joint on top of flush mortar joints. Pencilingis a purely decorative, painted surface treatment over a mortar joint, often in a contrasting color.

Masonry Units.The masonry units should also be examined so that any replacement units will match the historic masonry. Within a wall there may be a wide range of colors, textures, and sizes, particularly with hand-made brick or rough-cut, locally-quarried stone. Replacement units should blend in with the full range of masonry units rather than a single brick or stone.

Matching Color and Texture of the Repointing Mortar

New mortar should match the unweathered interior portions of the historic mortar. The simplest way to check the match is to make a small sample of the proposed mix and allow it to cure at a temperature of approximately 70 degrees F for about a week, or it can be baked in an oven to speed up the curing; this sample is then broken open and the surface is compared with the surface of the largest “saved” sample of historic mortar.

If a proper color match cannot be achieved through the use of natural sand or colored aggregates like crushed marble or brick dust, it may be necessary to use a modern mortar pigment.

During the early stages of the project, it should be determined how closely the new mortar should match the historic mortar. Will “quite close” be sufficient, or is “exactly” expected? The specifications should state this clearly so that the contractor has a reasonable idea how much time and expense will be required to develop an acceptable match.

The same judgment will be necessary in matching replacement terra cotta, stone or brick. If there is a known source for replacements, this should be included in the specifications. If a source cannot be determined prior to the bidding process, the specifications should include an estimated price for the replacement materials with the final price based on the actual cost to the contractor.

Mortar Types
(Measured by volume)
Designation Cement Hydrated Lime
or Lime Putty
Sand
M 1 1/4 3 – 3 3/4
S 1 1/2 4 – 4 1/2
N 1 1 5 – 6
O 1 2 8 – 9
K 1 3 10 – 12
“L” 0 1 2 1/4 – 3
Suggested Mortar Types for Different Exposures
  Exposure
Masonry Material Sheltered Moderate Severe
Very durable:
granite, hard-cored brick, etc.
O N S
Moderately durable:
limestone, durable stone, molded brick
K O N
Minimally durable:
soft hand-made brick
“L” K O

Summary

For the Owner/Administrator.The owner or administrator of a historic building should remember that repointing is likely to be a lengthy and expensive process. First, there must be adequate time for evaluation of the building and investigation into the cause of problems. Then, there will be time needed for preparation of the contract documents. The work itself is precise, time-consuming and noisy, and scaffolding may cover the face of the building for some time. Therefore, the owner must carefully plan the work to avoid problems. Schedules for both repointing and other activities will thus require careful coordination to avoid unanticipated conflicts. The owner must avoid the tendency to rush the work or cut corners if the historic building is to retain its visual integrity and the job is to be durable.

For the Architect/Consultant.Because the primary role of the consultant is to ensure the life of the building, a knowledge of historic construction techniques and the special problems found in older buildings is essential. The consultant must assist the owner in planning for logistical problems relating to research and construction. It is the consultant’s responsibility to determine the cause of the mortar deterioration and ensure that it is corrected before the masonry is repointed. The consultant must also be prepared to spend more time in project inspections than is customary in modern construction.

For the Masons.Successful repointing depends on the masons themselves. Experienced masons understand the special requirements for work on historic buildings and the added time and expense they require. The entire masonry crew must be willing and able to perform the work in conformance with the specifications, even when the specifications may not be in conformance with standard practice. At the same time, the masons should not hesitate to question the specifications if it appears that the work specified would damage the building.


Conclusion

A good repointing job is meant to last, at least 30 years, and preferably 50- 100 years. Shortcuts and poor craftsmanship result not only in diminishing the historic character of a building, but also in a job that looks bad, and will require future repointing sooner than if the work had been done correctly. The mortar joint in a historic masonry building has often been called a wall’s “first line of defense.” Good repointing practices guarantee the long life of the mortar joint, the wall, and the historic structure. Although careful maintenance will help preserve the freshly repointed mortar joints, it is important to remember that mortar joints are intended to be sacrificial and will probably require repointing some time in the future. Nevertheless, if the historic mortar joints proved durable for many years, then careful repointing should have an equally long life, ultimately contributing to the preservation of the entire building.

Selected Reading

Ashurst, John & Nicola. Practical Building Conservation. Vol. 3: Mortars, Plasters and Renders. New York: Halsted Press, a Division of John Wiley & Sons, Inc., 1988.

Cliver, E. Blaine. “Tests for the Analysis of Mortar Samples.” Bulletin of the Association for Preservation Technology.Vol. 6, No. 1 (1974), pp. 68-73.

Coney, William B., AIA. Masonry Repointing of Twentieth-Century Buildings. Illinois Preservation Series. Number 10. Springfield, IL: Division of Preservation Services, Illinois Historic Preservation Agency, 1989.

Davidson, J.I. “Masonry Mortar.” Canadian Building Digest.CBD 163. Ottawa, ONT: Division of Building Research, National Research Council of Canada, 1974.

Ferro, Maximillian L., AIA, RIBA. “The Russack System for Brick and Mortar Description: A Field Method for Assessing Masonry Hardness.” Technology and Conservation.Vol. 5, No. 2 (Summer 1980), pp. 32-35.

Hooker, Kenneth A. “Field Notes on Repointing.” Aberdeen’s Magazine of Masonry Construction.Vol. 4, No. 8 (August 1991), pp. 326-328.

Jedrzejewska, H. “Old Mortars in Poland: A New Method of Investigation.” Studies in Conservation. Vol. 5, No. 4 (1960), pp. 132-138.

“Lime’s Role in Mortar.” Aberdeen’s Magazine of Masonry Construction. Vol. 9, No. 8 (August 1996), pp. 364-368.

Phillips, Morgan W. “Brief Notes on the Subjects of Analyzing Paints and Mortars and the Recording of Moulding Profiles: The Trouble with Paint and Mortar Analysis.” Bulletin of the Association for Preservation Technology. Vol. 10, No. 2 (1978), pp. 77-89.

Preparation and Use of Lime Mortars: An Introduction to the Principles of Using Lime Mortars.Scottish Lime Centre for Historic Scotland. Edinburgh: Historic Scotland, 1995.

Schierhorn, Carolyn. “Ensuring Mortar Color Consistency.” Aberdeen’s Magazine of Masonry Construction.Vol. 9, No. 1 (January 1996), pp. 33-35.

“Should Air-Entrained Mortars Be Used?” Aberdeen’s Magazine of Masonry Construction.Vol. 7, No. 9 (September 1994), pp. 419-422.

Sickels-Taves, Lauren B. “Creep, Shrinkage, and Mortars in Historic Preservation.” Journal of Testing and Evaluation, JTEVA.Vol. 23, No. 6 ( November 1995), pp. 447-452.

Speweik, John P. The History of Masonry Mortar in America, 1720-1995. Arlington, VA: National Lime Association, 1995.

Speweik, John P. “Repointing Right: Why Using Modern Mortar Can Damage a Historic House.” Old-House Journal.Vol. XXV, No. 4 (July-August 1997), pp. 46-51.

Technical Notes on Brick Construction.Brick Institute of America, Reston, VA.

“Moisture Resistance of Brick Masonry: Maintenance.” 7F. February 1986.

“Mortars for Brick Masonry.” 8 Revised II. November 1989.

“Standard Specification for Portland Cement-Lime Mortar for Brick Masonry.” 8A Revised. September 1988.

“Mortar for Brick Masonry-Selection and Controls.” 8B Reissued. September 1988. (July/August 1976).

“Guide Specifications for Brick Masonry, Part V Mortar and Grout.” 11E Revised. September 1991.

“Bonds and Patterns in Brickwork.” 30 Reissued. September 1988.

Useful Addresses

Brick Institute of America
11490 Commerce Park Drive
Reston, VA 22091

National Lime Association
200 N. Glebe Road, Suite 800
Arlington, VA 22203

Portland Cement Association
5420 Old Orchard Road
Skokie, IL 60077


Acknowledgments

 

Robert C. Mack, FAIA, is a principal in the firm of MacDonald & Mack, Architects, Ltd., an architectural firm that specializes in historic buildings in Minneapolis, Minnesota. John P. Speweik, CSI, Toledo, Ohio, is a 5th-generation stonemason, and principal in U.S. Heritage Group, Inc., Chicago, Illinois, which does custom historic mortar matching. Anne Grimmer,Senior Architectural Historian, Heritage Preservation Services Program, National Park Service, was responsible for developing and coordinating the revision of this Preservation Brief, incorporating professional comments, and the technical editing.

The authors and the editor wish to thank the following for the professional and technical review they provided: Mark Macpherson and Ron Peterson, Masonry Restoration Contractors, Macpherson-Towne Company, Minneapolis, MN; Lorraine Schnabel, Architectural Conservator, John Milner Associates, Inc., Philadelphia, PA; Lauren B. Sickels-Taves, Ph.D., Architectural Conservator, Biohistory International, Huntington Woods, MI; and the following National Park Service professional staff, including: E. Blaine Cliver, Chief, Historic American Buildings Survey/Historic American Engineering Record; Douglas C. Hicks, Deputy Superintendent, Historic Preservation Training Center, Frederick, MD; Chris McGuigan, Supervisory Exhibits Specialist, Historic Preservation Training Center, Frederick, MD; Charles E. Fisher, Sharon C. Park, FAIA, John Sandor, Technical Preservation Services Branch, Heritage Preservation Services, and Kay D. Weeks, Heritage Preservation Services.

The original version of this brief, Repointing Mortar Joints in Historic Brick Buildings, was written by Robert C. Mack in 1976, and was revised and updated in 1980 by Robert C. Mack, de Teel Patterson Tiller, and James S. Askins.

Washington, D.C.  October, 1998

 

 

Home page logo: Soft mortar for repointing. Photo: John P. Speweik.

 


 

This publication has been prepared pursuant to the National Historic Preservation Act of 1966, as amended, which directs the Secretary of the Interior to develop and make available information concerning historic properties. Technical Preservation Services (TPS), Heritage Preservation Services Division, National Park Service prepares standards, guidelines, and other educational materials on responsible historic preservation treatments for a broad public.


 

 

Preservation Briefs | Questions
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48 Responses to “Historic Mass Masonry Restoration Discussion”

  1. Timothy
    July 5, 2012 at 4:39 am #

    Hi,

    Just as some other participants I got interested in the structural issues of restoration mentioned in the comments.

    I would like to get deeper into the study on the subject and I have found this online course:

    http://unaus.eu/index.php/online-courses-repair-and-restoration-for-sustainable-architecture

    Is there somebody who has any opinion on its list of themes that are studied? Would it be worthwhile?

    Thanks.

    • mkev
      July 9, 2012 at 10:06 am #

      Timothy,
      Nice to hear about your interest in the topic of masonry preservation and restoration. If you are working in the geographic area covered by the course, it looks pretty good to me. I say that because the course appears to concentrate on regional or local types of historic construction which I can understand. A lot of the knowledge will be transferrable but some construction types are geographically specific as are the codes and standards.

      I would check into the quality of the materials available. On line courses of this nature will need lots of high quality photographs etc. I have no experience with this particular course or institution so I can’t give any advice in that area. And, of course, nothing beats seeing the examples for real so hopefully you can view structures or buildlings in your area as you take the course and use those to generate questions and comments for the course.

      If you take the course, I would appreciate hearing your comments or assessment when you are finished. Good luck. M-Kev

      • Timothy
        August 28, 2012 at 2:14 am #

        Dear M-Kev,

        Sorry for my late reply.

        Thank you very much for your message and advice, I agree with you on all the points. I have seen some comments on another restoration course the same organization is offering (in Spanish) and they seem to be quite positive so I think I’ll give it a try this autumn. I’ll send you my opinion after finishing the course!

        Thanks again.

        All the best,

        Timothy

  2. Erik Valentino
    October 7, 2011 at 2:52 pm #

    I appreciate all the comments, I did my best to respond below to as many as possible in the order they were posted.

    The common themes seemed to be uncovered conditions and dealing with structural integrity. The soundness of a masonry wall can be determined in many ways. There are a variety of non-destructive test methods available, such as infrared photography, impact echo, ground penetrating radar, laser scanning, manual localized sounding, ultrasonic testing, pachometers and metal detection, and a variety of water and air testing methods. But they are just tools that should be combined with other tools such as exploratory probes and tactile visual operations to provide overall direction for the building. It is very difficult, without cutting a probe in the wall, to identify amounts of steel corrosion, flashing detailing and difficult geometry. Sounding a wall with a hammer is very effective and we do this as a project progresses. Additionally visual clues, such as cracking, out-of-plane displacement, bulging, spalling, and staining, will suggest that certain areas are not sound and require rebuilding. An informative and obscure book on masonry deterioration is the European Commission Damage Atlas – Damage Patters Found in Brick Masonry; very visual and helpful. A very effective method we employ is the Pilot Phase. This is where we take a small chunk in size and cost of the project and perform the repairs. This allows us to refine the cost and scope of the project, look for unforeseen conditions, reduce change orders, give the owner a comfort level, and also test the demolition and restoration techniques. Our theory is that we seek out clients that have buildings for the long-term and know they want to properly maintain them and do the repairs in accordance with the appropriate guidelines and standards. That in turn allows us to do better work.

    The concrete slab was replaced approx. 150′ above grade at the balcony level. The steel beams were cut in two and fed into the tower and then spliced back together with full depth welds.

    The steel beams to launch the scaffold were erected blindly in certain areas. Planning and coordination on-site were critical with the crane operator talking directly to the steel workers and riggers to position and shift the steel as it was set.

    Every building is different, but many do require steel to be replaced, since it has corroded and lost section. There are cases in mass masonry walls where no steel needs replaced. It is always done carefully and often temporary braces or containment needs setup just to do the demo.

    There is no building that cannot be restored with enough time and money. It typically boils down to an owner generated budget decision as to whether or not a building will be restored. Often damage is significant and we have seen buildings be completely demolished.

    The Lewisburg job was approx. $2M. Repointing varies with each building, mortar hardness and host masonry (brick, terra cotta, stone, etc.). It can range from $2-10 per linear foot. As an example, in a typical square foot of modular brick wall there are 7-7.5 lf of mortar joint and costs say $25/sf to repoint plus access. I would steer clear of Means for restoration work if you can. To do it right, it really takes more to do it in accordance with the guidelines. Don’t forget you need to get to the work area (access), you will burn out many diamond cutting blades, grinders, saws, the labor and material to remove and repoint the joints, detergents to clean the wall, etc. And you can’t do all the steps right in a row, there are delays for drying, curing, cleanings. It all adds up. There are many cheap ways to repoint a wall and many methods, but if it is not done correctly – it will NOT perform. You need to be careful in promising an owner your repointing will last 100 years, since mortar is sacrificial and is a maintenance item. We feel comfortable with saying 50 years, but environmental conditions are of great influence. Say for example the mortar you are removing is very hard and requires two saw-cuts to remove, this will drive the costs up quickly.

    There are always creative ways to fix old and new buildings to make them function better. It is often a compromise between form and function, but generally a method is available.

    With experience, it does become easier to identify matching brick and mortar, but there are still several logical steps that need to be taken to make it work. Materials vary widely from project to project, but usually run 10-15% of the project.

    Unforeseen conditions are a big factor in our business. We typically have a good feel for what it takes to surmount these challenges because of our experience. But we often recommend contingency money be set aside for such items, say 10%. Also unit costs are used when possible. It is difficult to bid, that is why there are a lot of poor quality projects being done out there.

    There are project profiles of other projects on our website that can be reviewed.

    Structural repairs were probably 70% of the project costs, but it depends on your definition. If it means something will fail, then mostly our work falls into that category.

    We work all over the mid-Atlantic region, from NY to SC. We do consulting outside of that area as well. Weather needs to be matched with the materials being used to ensure they function properly.

    New construction masons are typically dealing with more production type issues and only laying masonry, whereas a restoration mechanic “mason” is more skilled at the details required to make the restoration work properly and also dealing with flashing, sealants, and other materials. We have sourced white sand before, but locating a matching sand is always a challenge, and you really need to do due diligence in matching sand. We see chemical deterioration in natatoriums and water treatment plants. As far as jailhouse tips; placing a bar of soap in a tube sock makes a very effective weapon.

    The original mortar was tested to determine constituents and strength, and a softer Type N mortar was used for repointing. That was the extent of lab testing required for this project.

    The area of the tower below the work area where the scaffold would bear load was mass masonry walls approx. 2’ thick and did not have damage. The scaffold imposed loads were designed based on not largely interacting with any deteriorated areas since they would require repair.

    Several holes were cut into the host structure to accommodate the scaffold beams. The holes were cut with hydraulic masonry diamond chainsaws. The openings were then prepped with grout and steel bearing plates for the beams. The openings were then toothed in with new masonry at project end. Every project is different as far as schedule, but we try to allocate a few weeks to accommodate for conditions and weather.

    I was interested in solving problems and getting involved in a variety of building types, so I thought the repair and restoration business was a good choice for me after graduation. Personally, just doing design on multi-year projects with little variety did not appeal to me. Although it turned out well for me, I should have done some pure design for 2 years and then went into restoration. We try to mitigate danger at all levels, and through planning and stabilization are able to work on more difficult buildings.

    We did not review seismic retrofit for the tower, but as with any mass masonry structure, it would require overcoming significant geotechnical and structural issues.

    Any project that we can extends it service life into the future are project I enjoy working on. I hate to lose neat buildings that are part of our architectural heritage. I do enjoy a blend of field and office work.

    It is very difficult for an owner to get the same value we provide from other contractors. We do our best to negotiate projects and build relationships with quality clients, which provides the best value for clients. In bidding situations, we like to ensure there are heavy restoration pre-qualification requirements to keep the playing field level.

    Many times with deteriorated masonry, the work sequencing needs to be carefully planned to be able to remove bad areas of masonry without affecting larger areas while the repair s in process. Typically this can be accomplished by isolating smaller areas with shelf angles or even temporary structural steel to be able to accomplish the repairs. Sometimes the building may need a top down approach and vice-versa.

    There are test methods to test the strength of both brick and mortar and can be applied if justified. If the wall is heavily weathered from water infiltration and the bond between the brick and mortar was compromised, the wall strength will be diminished.

  3. StephenK
    September 20, 2011 at 2:53 am #

    In response to Kyle’s comment – I imagine they could probably use some of those same techniques Steve was talking about. With infrared you could detect deterioration due to water inside a brick, although I do not know how well that would work with only one brick. In response to the mortar comment Kyle made, I remember concerns were being brought up with Millennium Science Complex half-brick facade panels due to the different expansion and contraction rates of the brick and concrete. However, the mortar is pulverized anyway by the sheer weight of the masonry, so maybe the different contraction and expansion rates do not affect their performance enough to raise concern – I was under the impression that color was a factor due to aesthetics.

  4. Raffi K
    September 19, 2011 at 6:10 pm #

    Reading some of the comments, it seems that I am not the only one that didn’t take masonry as Christy and Cadell didn’t either. It seems everyone agrees that details are the most important in masonry restoration ranging from the color, the texture, and the material. This is time consuming and costly for owners thus a lot of cooperation is needed between the contractor and the client. I agree with Brian Brunnet that The Lewisburg Federal Project shows a low budget project in details which really helped me in seeing how the contractor is responsible to come up with cost effective solutions. However, what I would like to stress on is the calculations/considerations involved in these types of restorations. It seems the main concerns are the materials and the cohesiveness of the overall look of the façade and not the integrity of the structure. True that the new materials are better and more effective but is there special considerations or calculations? There must be otherwise artists can restore buildings. Thanks for everyone’s input and discussions this was really helpful.

  5. MKostick
    September 19, 2011 at 5:09 pm #

    Echoing some of the previous comments about the amount of consideration involved in choosing a mortar/brick color, I have added a link to a photo that I took of what I assume to be a wall mockup for the new Biobehavioral Health Building on campus.

    http://imageshack.us/photo/my-images/850/62611to91911106.jpg/

    The mockup was placed next to the adjacent Henderson Building for comparison. The sign atop the wall lists the different types of mortar (top & bottom) used in the assembly. I think the brick color and style and the actual mortar jointing helps the assembly match almost perfectly to the neighboring building.

    While I was in the Henderson vicinity, I took a look at the retaining wall in response to Professor Parfitt’s comment. The cracking and loss of mortar, along with the minor spalling along the edge of the stone blocks is evident in the following photo link.

    http://imageshack.us/photo/my-images/215/62611to91911107.jpg/

    I am not sure if this is the same location as specified in his post, but it offers a great hands-on look at weathering effects of masonry structures.

    The information and links Nicole has provided are very useful and enlightening. I especially enjoyed the presentation by Gale Associates. Their one statement, “Proper detailing is the key to success.” really sums up how to prevent deterioration of masonry structures.

    As a segue into this week’s lecture and discussion, it seems that a large majority of masonry failures and deterioration stem from a common root, water/moisture infiltration.

  6. SPfund
    September 19, 2011 at 4:57 pm #

    In reply to Ksenia’s comment about my original question on structural integrity of masonry I decided to do some research of my own research on the topic and give the class some links in case they’re interested.

    There are many techniques for “Non-Destructive Evaluation” of historic masonry structures. I found a case study on Preservapedia, of the New York State Capitol Building, that was very informative about the project and NDE in general. Multiple techniques were used on this building including: Impule Radar, Impact Echo, Ultrasonic Pulse Velocity, and others. I have included the link below:

    http://preservapedia.org/Non-destructive_testing_for_masonry-_part_2#Impulse_Radar

    I have provided another link below specifically about investigations using infrared thermagraphy in India. This is a very popular technique for identifying moisture problems in masonry structures.

    http://www.goinfrared.com/media/2007-067Rao.pdf

  7. MVandersall
    September 19, 2011 at 4:37 pm #

    Thanks Ryan for posting that information about selecting the appropriate mortar. It seems quite complicated that so many factors can go into simply selecting the mortar as evident in the article above on “Repointing Mortar Joints in Historic Masonry Buildings.” It is fairly apparent however that the mortar is one of the most critical pieces to the puzzle. As pointed out in the article “A good repointing job is meant to last, at least 30 years, and preferably 50- 100 years.”

  8. ktennant
    September 19, 2011 at 4:08 pm #

    There seems to be an emphasis on making sure that the mortar is matched to existing in order to make sure that the replacement mortar is not so strong that the masonry cracks instead. I thought I would also point out that in cases is it a good idea to also find a way to test the strength of the masonry units since this could also vary some? Especially in a case where you are unable to make a good determination of how strong the masonry is. Does the masonry strength diminish much over time due to weathering effects?

  9. cdipaolo
    September 19, 2011 at 3:16 pm #

    I have to agree with Cadell. I never took a masonry class either therefore; most of the information was entirely new to me. I also am very curious as to the structural integrity question.
    I really enjoyed the emphasis on matching the mortar. I have seen many repointing jobs where the contractors just didn’t take the existing mortar properties into account at all. It really leaves the job looking incomplete. Putting in the time and energy to pay attention to the details can easily make the finished product worth the money to repoint. Thank you again Erik for showing us many of the different aspects of the project where MPS did the extra work to make sure the finished product was the best it could be.
    Lastly, thanks BRose for your extra effort in looking up the prices. I was looking for the answers to those questions in addition to mine and it is nice to have a base estimate.

  10. JennyT
    September 19, 2011 at 3:05 pm #

    Many of the comments seem to focus on the intricacies associated with the mortar used in restoration projects (color, strength, etc.), which I as well found to be a very interesting process and learned a lot about through the readings and presentation. However, while the mortar mix is important, I feel that matching new brick to existing brick in the projects can be must as time consuming and meticulous of a task. I also feel it is equally as important because that is what most people are going to notice about the restoration when looking at a building at first glance. I think the quality of well done historical restoration projects is really impressive.

  11. CBehm
    September 19, 2011 at 2:53 pm #

    I think the reading accurately stressed the importance of the attention to detail that needs to be paid for masonry restoration projects. The reading stated main points that needed to be followed to end with a successful project, a few of the main ones are as following:

    – Choosing the right mortar, based on color/texture and strength
    – Properly repointing
    – Budgets/scheduling and hiring an experienced contractor

    The presentation reinforced what we learned with the reading, seeing how many obstacles had to be overcome to have a final product that the owner was pleased with. Making the restoration work blend into the original structure was of the utmost importance and this was achieved by following all the guidelines that were stated in the reading.

  12. BRose
    September 19, 2011 at 2:37 pm #

    After doing alittle research I think I’ve found a ballpark for a cost estimate, which a may answer some questions Nate, Josh and myself had.

    According to RS Means 2000:

    “Clean and point: smooth brick and rough brick” is about $1.50 per SF.
    “Sawing: Brick or block by hand, per inch depth” is about $1.20 per LF. Assuming 4″ nominal brick height and sawing an average or 1″ back, that gets $3.60 per SF. This totals abut $5 per square foot. This doesn’t take into account scaffolding, access, replacing brick, etc.

    According to a contractor’s FAQ forum, http://www.contractortalk.com/f48/how-do-i-price-pointing-brick-45437/
    $5 a SF for ground-level repointing is a valid estimate.

  13. CadellC
    September 19, 2011 at 1:39 pm #

    I agree with Ksenia and Steve Pfund and I think that the whole class would appreciate an answer to how structural soundness is determined.

    Having not taken masonry engineering, I was unaware of some of the intracacies of masonry engineering, including mortar strength. The readings, the presentation, and this discussion allows me to be better prepared for masonry class. It had never dawned on me that the mortar had to be more permeable and softer than the surrounding masonry. Thinking about this in the context of tearing a masonry building down makes sense. You can always find whole bricks (typically lots of them) when a masonry wall falls down, but to find a mortar joint that is intact is nearly impossible. Thus the mortar is weaker than the brick.

    Thanks again Mr. Valentino for the presentation.

  14. Bbrunnet
    September 19, 2011 at 1:25 pm #

    As many of our other classmates have stated, it really is intriguing to see how much effort and involvement is included in the topic of building restoration. From mortar color to its pointing style, the detail to match each element of the previous structure is amazing. Many owners in turn need to be somewhat flexible when it comes to restoration projects, allowing for possible unseen repairs and damages that may be hidden within the masonry.

    I really do see how much cooperation is needed between the owner and the contractors, because you do not want to try and go over budget on the project, however you want to provide a quality restoration that will last for many years to come. I enjoyed how the presentation followed through the Lewisburg Federel Penitentiary project step by step so that we could see how to apply low budget solutions to a project. One such solution was to add the small piece of flashing to the center of each merlon, which drove water and moisture out of the center. This small bit of flashing will help the building last for many more years to come. The lecture benefited as a great learning experience and allowed us to see how building restoration can provide many different challenges to an engineer.

    Thanks again!

  15. Ksenia
    September 19, 2011 at 12:48 pm #

    Steve Pfund actually brought up a great question to which I’d be really curious to know the answer-

    if the structural condition of masonry walls is generally an unknown before you open up the wall, what sort of testing would you need to do in order to know if the wall on which you build your scaffolding can actually support the loads you intend to put on it?

    Do you use any noninvasive testing techniques like impact-echo or thermography? How much information would a technique like this provide about the load-bearing capacity of a historic structure?

    I’m sorry for contributing more questions, I’m just rather curious about structural testing techniques… I’d imagine it’d be something that you’d need experienced engineers and masons to carry out, which means us fledgling AEs that just flew the coop couldn’t get into historic restoration for quite some time. It seems like a lucrative field.

    Thank you again!
    K

  16. ZHott
    September 19, 2011 at 10:19 am #

    Proper selection of mortar is important, as stated in the readings; however, even if the engineer selects the correct mortar to match the strength, color, and pointing style of the previous mortar, as stated in the reading, the quality of work done by the mason is just as important. If the mason does not properly replace, it won’t last its expected life of (hopefully) 50-100 years.

  17. NBabyak
    September 19, 2011 at 9:41 am #

    Two of the major things that stood out for me during both the lecture and in the readings was the amount of preparation needed to properly analyze the problem and the attention to detail to properly execute the restoration. While theses ideas are important in all areas of design, it seems that a restoration project magnifies them immensely. Every member of the team has to execute their role in order to fix the problem and keep the problem from happening again.

    The National Park Service brief summarized each team role. The owner has to be ready for a long costly process and not rush the work to cut corners. I would hope that the owner has some sort of emotional investment in the building and wants to see the job done right. The design consultant must assist the owner in planning for logistical issues in construction and research. They must also be ready to spend time properly investigating the root cause of the issue. Having worked for a structural consultant firm, there were many times where we reused a detail or design from another project. On a restoration project, it seems very important to not assume a solution and to realize that each restoration is unique. The final member of the team is the mason. The mason is extremely important because they are the ones executing the design and providing the owner with the final project.

    It really stood out to me that each role is extremely important and vital to the success of the restoration project.

  18. DaveT
    September 19, 2011 at 9:03 am #

    As Becca stated previously, these lectures and selected readings give us a taste of topics beyond just design, which we are normally exposed to in the classroom. As soon to be professionals, it is important for us to see that proper planning and hacing some sort of oversight in construction is vital for a successful project. The fact that improper execution can ruin a project despite proper is always an eye opening thing to think about.

    What I enjoyed about this article was the emphasis on selection of mortar. I know from taking Masonry design, a higher emphasis was placed on the strength of the masonry and mortar as a topic was generally ignored. It was enjoyable to see the topic of mortar selection being discussed more thoroughly on these forumns. The following Masonry Magazine website further explores choosing the appropriate mortar for a specific project: http://www.masonrymagazine.com/9-02/mixing.html

  19. mkev
    September 18, 2011 at 11:18 pm #

    Thanks for the additional resources Nicole as well as your comments. Of the four Penn State OPP masonry projects in that contract that you reference, WJE’s Cleveland office (using several PSU AE alums) performed the assessment and designed repairs for IST, Pond and Pattee. Gary Wentzel, head of WJE’s Cleveland branch is scheduled to talk to the class later in the semester and perhaps he can provide some follow up or summary of that particular work. I have not seen the Gale presentation before but it was interesting and to the point of what we are studying. I think you will see something even more detailed from SGH on Tuesday. By the way, Gale is always looking for Penn State AE students for structural positions and for Building Technology so if anyone is interested, let me know and I’ll provide you with a contact in their Boston area office.

  20. JProgar
    September 18, 2011 at 9:47 pm #

    Seismic rehabilitation for mass masonry buildings may be requirements that must be designed and accounted for depending on the project. I looked a little deeper into seismic rehabilitation of mass masonry buildings after reading StephenK’s comment about the potential seismic restoration of the tower. Below is the link to the PDF that I used for this research:

    http://posts.same.org/frontier/PDFs/Seismic%20Renovation%20of%20Historic%20Masonry%20Buildings%20-%20NSF%20Template%A9%20(1).pdf

    Seismic issues for these mass masonry buildings include: Lack of reinforcing, rubble in-wall, weak mortar, existing cracks, and diaphragm connections to existing masonry, new loads on or adjacent to the foundations. A complete list is included on the attached PDF link.

    Seismic evaluation methods are based on the International Building Code (IBC), International Existing Building Code (IEBC) and Seismic Evaluation of Existing Buildings – ASCE/SEI 31-03.

    There are several methods for seismic rehabilitation in these mass masonry buildings. Below is a quick overview of different methods along with a brief description of the pros/cons of these systems:

    – Post-tensioned walls: the addition of steel reinforcement into the masonry wall using a drive mechanism and then applying a load to the reinforcement. This system does not require any new framing systems but it is difficult to drill through walls.
    – Core-Drilled Mild Reinforcement: the addition of steel reinforcement into the masonry wall using a drive mechanism without applying any load to the bars. This is very similar to the post-tensioned walls and requires the bars to be closely spaced together which increases cost.
    – Inlet Mild Reinforcement: the addition of steel reinforcement by removing masonry and replacing the void with concrete and steel reinforcement. This method allows for no damage to the exterior fabric of the building but may not work if the walls are rubble in-wall.
    – Fiber Reinforced Polymer: this method is the addition of a layer of a fiber reinforced polymer that does not require any intrusion in the masonry walls but is costly.
    – New Concrete Walls: the addition of an interior reinforced concrete wall which damages the fabric of the interior wall and is added cost but provides positive connections to the diaphragm.
    – New Masonry Walls: the addition of an interior reinforced masonry wall which requires no new additional framing but will require modifications to the existing foundations.
    – New Steel Shear Walls: the addition of an interior steel plate that is bolted into the masonry wall. This method may require new steel framing but has the same advantages of the new concrete or masonry walls.
    – New Steel Framing System: the addition of a structural framing system which has no alterations to the exterior fabric of the building but is costly and requires connection to the existing structural system.

    All the methods described above have similar pros and cons as shown in the attached PDF but require different levels of intrusion into the existing masonry walls. For more information about these different methods briefly described above, check out the PDF with pictures of how each system is constructed along with the entire list of pros and cons.

  21. BDick
    September 18, 2011 at 9:11 pm #

    I agree with a lot of the comments posted, especially since it is very true that we aren’t exposed to restoration work in our classes a lot. It was great seeing all the work and preparation that goes into this kind of work.
    I also found the reading to be really informative. I knew that choosing a mortar that was harder than the surrounding masonry would cause cracking in the masonry, but I never knew that you also had to be very careful with the choice of mortar used in restorations. There are a lot of factors that have to be considered that I wasn’t aware of. I though the “scavenger hunt” on campus was a great way to help us see what happens to mass masonry buildings over time because of these considerations, or a lack there of.

  22. mkev
    September 18, 2011 at 8:36 pm #

    Ryan makes a good point about the mortar. As I recall, there are a number of locations on campus including the outside retaining and entry wall at the old / historic orignal Human Development building (Henderson)where repairs have been made with a modern mortar that was harder than the original. The result was spalling of the stone due to pressure concentrations at the harder mortar areas that were not moving in a similar manner to the historic mortar.

  23. NTrujillo
    September 18, 2011 at 8:35 pm #

    In mass masonry construction, many failures occur in the forms of cracks in mortar joints, loose bricks, and damp walls. As it was said in the reading and in the presentation, identifying the problem is essential before repointing or the replacement of bricks. On the Masonry Preservation Services website, they provide a list of symptoms and causes: http://www.masonrypreservation.com/resources/symptoms-causes.asp.

    A failure of the mass masonry for the Lewisburg Federal Penitentiary was displacement due to the corrosion of the embedded steel. The expansion of the oxide layers of the steel ring beam caused the corbel to displace. It was replaced with stainless steel, a corrosive resistant material.

    I thought it was interesting to see the ASTM C-1601 testing chamber used for the Lewisburg Federal Penitentiary Renovation. The chamber measures how many gallons of water penetrate the brick area. Perhaps, Penn State IST Building would have benefitted through the use of the test. Through the Capitol Masonry Preservation Project, Penn State OPP plans to correct various brick masonry problems of the IST Building due to water penetration, including the “replacement of flashing systems, and corrections to bearing lintels and brick ledges” (http://www.opp.psu.edu/planning-construction/Projects%20Out%20to%20Bid/2009-web-announcement/PN09-41826.02).

    In the AIA Masonry Wall issues presentation by Gale Associates, they provide guidelines for mass masonry wall design (http://www.gainc.com/whats_new/AIA-Masonry%20Wall%20Issues.pdf). Two of their 5 “Rules of Thumb” for masonry wall design was to separate corrosion-prone materials from touching the interior face of walls and to allow wall components to dry using vapor permeable materials. Like Erik, said in his presentation it is important to have proper detailing to ensure long-term life of the building.

  24. RDalrymple
    September 18, 2011 at 8:02 pm #

    By doing the reading I found that there is a lot of work that is put into finding an appropriate mortar match when a historic building is repointed. There is a lot of research that needs to be done for the existing mortar so that the new mortar meets the requirements.

    The four most important aspects that a new mortar must have are:
    -It must match the color, texture and tooling of the existing mortar
    -The sand must match the sand
    -It must have be more permeable and be softer than the masonry units
    -It must be as permeable and as soft as the existing mortar

    These are all important qualities of the new mortar that will be used for the repointing of a building. Testing and analysis must be done in order to determine these properties. There are many different analysis methods that can be used, although the correct one must be chosen for each case because there are advantages and drawbacks to each method. I find it interesting that the selection of the new mortar is so complex and requires so much testing and research. If the proper steps are not taken and an insufficient mortar is used, then it can cause damage to the masonry building, and be very costly in the future.

  25. cdipaolo
    September 17, 2011 at 11:05 pm #

    Thank you so much for the presentation. I noticed you got to work on some great projects from the sheets you sent around in class. It was amazing how perfectly the tower matched the original after your team was finished their work. I am curious, how does MPS competitively bid on projects when they clearly are not just trying to fix whats there but to also improve the system to work better? It seems like MPS tends to go above and beyond to give the client the best product possible whereas I am sure other companies are more worried about the low bid.

    Also, I am extremely interested in the answer to Ksenia’s answer about how to deal with a project that is structurally unsound. In addition, you mentioned sometimes being surprised at how badly structural systems can be damaged when you finally open up the masonry. Have you had any projects where when you open up the masonry wall the structural system is structurally unsound? If so how did you deal with that situation?

    Thanks again!

  26. NTrujillo
    September 16, 2011 at 3:43 pm #

    Erik,

    I enjoyed your presentation yesterday. It was very interesting to know all of the obstacles that can arise in historic preservation projects. In the industry, I know you had discussed the hesitation from many owners to invest in the specific maintenance procedures necessary for mass masonry due to cost. Many due to not want investigate the root cause of their problem, such as structural steel corrosion. But it seems that it would make much more sense for the long term life and maintenance costs for the building. What type of other non-destructive evaluation tests can be to demonstrate these more effectively to all owners?

    Thank you,
    Nicole

  27. ktennant
    September 16, 2011 at 3:42 pm #

    Thank you for taking time to come and speak to us about masonry preservation. It’s an interesting and important topic and even more interesting project! So many things had to be considered in order to make it authentic to the original, durable for the future, and a safe work site. Would you rather work on a restoration project like this that requires a lot of demolition and new construction to match original? Or would you rather work on smaller projects that are more preventative in nature?

    It is definitely nice to hear about structural related jobs that don’t require new construction. What was it about the field of preservation specifically that drew you in? I have sometimes wondered if something like this would be more enjoyable since you probably get to spend more time away from the computer and outside.

  28. StephenK
    September 16, 2011 at 3:41 pm #

    Erik, thank you for coming in and talking about this project – it was a very fascinating presentation. Mass masonry structures, especially those with the aesthetic that was chosen for the prison tower, are a bit more intricate than I had expected. A lot of planning went into this project, and it was impressive to see it all come together in your presentation.

    I have a question about the potential seismic restoration of this tower. How would you ensure that the tower would meet seismic codes without affecting its aesthetics and without structurally compromising it in the process (there is undoubtedly more than one solution for this, but I am asking how you would go about it). I understand that the answer is probably far more complex for this venue, but I would appreciate any sort of answer you could share.

  29. Raffi K
    September 16, 2011 at 3:27 pm #

    Mr, Valentino,

    Thanks for taking some time and coming to our class for a wonderful presentation about masonry and restorations.

    My question regards on your journey to where you are right now. From your bio I have seen that you have worked on valuation, repair, and restoration of building façades for a long time now. Every student strive for the best, the newest, and most efficient designs. What attracted you as a youngster to go in the restoration and repair of old buildings instead of designing new buildings? Also my other question would be what was the most dangerous or exciting repair that you experienced as sometimes old buildings tend to behave in a more fragile manner?

    Again thank you for coming.

  30. MKostick
    September 16, 2011 at 3:23 pm #

    Eric,

    I really appreciated your lecture on historic masonry preservation. It was amazing to see just how far the Lewisburg Federal Penitentiary tower had fallen into disrepair. The amount of effort it took to properly restore this landmark is extraordinary. I really thought it was interesting that MPS not only repaired the structural issues with the tower, but did so in a away to maintain its visual aesthetics. (i.e. brick color and hiding the drip edge)

    I have a question regarding the scaffold system for the restoration. You showed a picture of a crane threading the initial beams through the tower on which the rest of the system would be errected. Where there any alterations, such as cutting holes in the structure, to allow for the installation? If so how were these areas corrected after the disassembly of the scaffold?

    You also made it evidently clear that you cannot be certain of the conditions of the underlying masonry or structure. In relation to this, do you typical set a schedule for a restoration project? If so how much time do you allow for such setbacks?

  31. SPfund
    September 16, 2011 at 3:10 pm #

    Erik,

    You and your crew did an excellent job on the tower and I enjoyed learning about it. It seems that you were able to consider everything necessary to perform this renovation flawlessly. I have a question about the structural integrity of the old existing tower with regard to your temporary scaffolding.

    I understand it was concluded that the tower was structurally adequate to carry the loads of the scaffolding, your crew, and materials, but how did you determine this? Was there damage to the tower below the section you were renovating? Was there water entering from the openings in the top of the tower and causing degredation of material further down? What investigative and analytical techniques did you employ to conclude the tower could handle the extra loads with all the weathering and damage?

  32. MVandersall
    September 16, 2011 at 3:05 pm #

    Eric,

    Thank you for the presentation on the restoration of the central tower of the Lewisberg Federal Penitentiary. I found it to be very educational and inciteful. One comment I have is how much testing was done during the analysis phase when you were still planning the restoration? Since the mortar of the bricks which were being replaced should not exceed the strength of the existing mortar, how much testing was done in preparation for the restoration? Thank you once again for taking the time to provide us with a lecture on building restoration.

  33. CadellC
    September 16, 2011 at 2:53 pm #

    Mr. Valentino,

    Thank you for speaking to us about masonry restoration. It was really interesting to learn about other options in an AE career.

    I have worked with masons before, but these masons have only ever done new masonry work. What, if any, is the difference between a regular mason and a restoration mason? Also, the masons I have worked with said it is difficult to find white sand for white mortar (typically for use with white brick). Is this true and if so, what might be a work around to restoring grout when the original sand can no longer be found at a reasonable cost?

    I realize water and regular weather is the biggest cause to masonry deterioration. Do you ever see any chemicals that deteriorate the masonry in ways unlike water? (ie. acid rain or chemicals in a manufacturing facility)

    You had mentioned you have some jailhouse tips. What might some of those be?

  34. Bbrunnet
    September 16, 2011 at 2:48 pm #

    Eric,

    Thanks for coming to our class for a great presentation. I never would have thought how much work and detail is involved in restoring a masonry structure. I was also surprised to see how your company erected the scaffolding to work in such a difficult area.

    My question regards project locations. At the lecture, I have seen that you have worked on many restorations in Pennsylvania. Have you worked on any other projects outside of the state, or in other parts of the country? Have you worked in other countries on any restoration sites? If so, what kinds of restoration projects were those. Also, I saw you had to deal with changing weather conditions on the jobsite. Have you ever experienced any special cases of weather on site that is not typical of our climate here in Pennsylvania?

    Thanks.

  35. RDalrymple
    September 16, 2011 at 2:46 pm #

    Thanks for coming and talking to us about this unique restoration project Erik. That must have been quite an experience working on a project at a high security prison.

    During your presentation you spoke about the structural repairs that were done on the tower as well as the exterior repairs that were done on the masonry mainly for aesthetic reasons. What percentage of the total cost of the project went to structural repairs?

  36. CBehm
    September 16, 2011 at 2:45 pm #

    Erik,

    Thank you for taking time to give us the historic masonry preservation presentation in class. I was not aware of how much plan preparation goes into these types of projects to ensure the customer is satisfied with the final product. I think it’s important that we keep these older buildings from falling into complete disrepair just because of shear neglect.

    I really enjoyed learning about the Central Tower at Lewisburg Federal Pen, but I was also intrigued by the flyer you passed around about the restoration work at Fallingwater. Could you provide more details on challenges of that project?

  37. JProgar
    September 16, 2011 at 1:57 pm #

    Erik,

    Thank you for a very interesting presentation. In our curriculum we study how to design and build new buildings and are not exposed to restoration of existing structures as much. With that said, I was very impressed with the amount of planning required prior to the restoration work itself.

    During your presentation, the one item that I kept asking myself over and over was about bidding restoration projects in general. You said in the presentation that when you open up an existing masonry wall you don’t know what existing conditions you’ll find. How do you account for the potential of additional scope of work that may not be known when you submit a bid? Is everything based on a unit cost? It seems like this kind of work would include a large number of change orders unless money was alotted for these unforseen conditions when the final bid is submitted.

  38. NBabyak
    September 16, 2011 at 1:56 pm #

    Erik,

    Thanks for taking taking time out of your schedule to come to our class and share a little bit of what you do with us. It was an interesting and informative presentation. During the presentation, you talked about doing your best to match new brick and mortar characteristics with the original brick and mortar, adding that it took months of testing and fabrication. For renovation projects, how difficult is it to find this right match? Is it possible to look at the original brick that is being restored and know almost immediately what its material characteristics are within reason? In addition, what percent of the total cost ends up going to matching these properties?

  39. JennyT
    September 16, 2011 at 1:29 pm #

    Hey Erik, thanks for a very interesting presentation. During the presentation you talked a lot about flashing and restoring the tower with newer technology that will make it last longer. In this case, with the height, the modern additions would never be noticed. Would this still be added to more accessible buildings and would there ever be instances where you add in expansion joints or other newer techniques in the restoration, or would this be too obvious of a change and take away from the historical nature of the structure?

  40. BRose
    September 16, 2011 at 1:25 pm #

    Thank you for the informative and interesting case study. It is really great to see all the different career paths a PSU AE has to choose from.

    I have a question concerning the cost involved with repointing and repairing masonary. What is a typical ballpark estimate for a straight-forward brick wall repointing? How much more would that square foot estimate be for a stone wall? If you’re able, how much is a complicated project like the Lewisburg Federal Pen.?

  41. ZHott
    September 16, 2011 at 11:21 am #

    Erik,

    Thanks for the great presentation. Has MPS ever encountered a building which simply can not be restored? Does MPS even consider that option when looking at a project? If so, could you give any details on the damage?

    Thanks.

  42. Ksenia
    September 16, 2011 at 10:39 am #

    Erik-

    I was pleasantly surprised by how interesting historic restoration can actually be. It takes a lot of forethought and planning to get all the construction to run smoothly, and it’s an impressive feat to avoid hiccups in the process. The intricacies of trying to predict brick/terra cotta shrinkage, coordinate material and shape choices as well as dealing with the countless site constraints takes careful consideration.

    How often, in your field, do you come across buildings where you need to tear out structural steel in order to properly restore the structure? Also, out of curiosity, how would you deal with restoring a structurally unstable masonry wall of some sort with no structural steel?

    Thanks!
    K

  43. DaveT
    September 16, 2011 at 8:34 am #

    Eric,

    Thanks for taking time out of your schedule to come and give us an awesome lecture on masonry preservation. I believe the statistic is that new construction of buildings accounts for only 2% of all buildings in existence. This makes it important that we look at keeping existing buildings in serviceable shape for occupant use.

    The one part of the lecture that interested me the most was where you stated the crane could only erect beams from one side of the tower, so some beams were “blindly” erected. How did MPS go about coordinating the placement of the steel beams when there is such a high liability that things can go wrong?

    Thanks.

  44. BDick
    September 16, 2011 at 12:44 am #

    I thought the lecture was very interesting. It’s amazing how a historic piece of architecture can be restored but still manage to retain it’s original look. That’s a huge part of historic restorations. I also thought the scaffolding system used for the project was really interesting and creative. It was a great solution to the requirements of working in a prison.

    I had one question about the slab replacement mentioned in the lecture. How were the new steel beams place inside the tower? Was it open to above so a crane could drop them in place inside the tower? In the photo it’s a little difficult to see where exactly the slab replacement occurred in the tower’s height.

    On a side note, I also have to say that I was very excited to find out the architectural inspiration for the Central Tower at the Lewisburg Federal Penitentiary was the clock tower in Piazza Pubblico since I was there earlier this summer. Sienna was a beautiful city and it was a nice reminder of the trip to Italy!

    Thanks!

  45. mkev
    September 15, 2011 at 11:40 pm #

    Thanks for the great presentation Erik! It was an excellent follow up to the mass masonry building exploration the students performed earlier this week relative to viewing Penn State’s oldest masonry structures not to mention a lead in to a lecture next week by Alex Kosis of SGH titled Waterproofing 101 which expands the discussion to cavity and barrier wall construction.

    One good point you made that I think is worth reinforcing is the fact that your goal was to improve on historic detailing with minimal or no impact on the historic fabric. The addition of non-original flashing in critical locations and even weeps in mass masonry is a concept worth pursuing.

  46. Erik Valentino
    September 14, 2011 at 6:02 pm #

    I look forward to sharing some information with the class during the masonry restoration presentation.

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