2 PRESERVATION 

BRIEFS 

Repointing Mortar Joints 

in Historic Masonry Buildings 

Robert C. Mack, FAIA 

John P. Speweik 

u.s. Department of the Interior 

National Park Service 

Cultural Resources 

Heritage Preservation Services 

Figure 1. After removing deteriorated mortar, an experienced mason repaints 

a portion of this early-20th century limestone building. Photo: Robert C. 

Mack,FAIA. 

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 (Fig. 1). 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: Repainting Mortar Joints in Historic Brick Buildings 

to 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. 

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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 cement was 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 (Fig. 2). The 

root cause of the deterioration-leaking roofs or gutters, 

differential settlement of the building, capillary action 

causing rising damp, or extreme weather exposureshould always be dealt with prior to beginning work. 

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 

Figure 2. Much of the mortar on this building has been leached away by 

water from a leaking downspout. The downspout must be replaced and any 

other drainage problems repaired before repainting. Photo: Robert C. Mack, 

FAlA. 

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 (AlC), the 

Association for Preservation Technology (APT), and local 

chapters of the American Institute of Architects (AlA). 

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. 

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 (Figs. 3-4). 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 
Figure 3. Good-quality repainting closely replicates the original in composition, texture, joint type and profile on this 19th century brick building (left), and on this 

late-19th century granite on H.H. Richardson's Glessner House in Chicago (right). Photos: Charles E. Fisher: Sharon C. Park, FAIA. 

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 sand in 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.) 

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 

Figure 4. (left) The poor quality of this repainting-it appears to have been " tooled" with the mason's finger-iloes not match the delicacy of the original beaded joint on 

this 19th-century brick wall. (right) It is obvious that the repainting on this "test patch" is not an appropriate replacement mortar joint for this early-19th century 

stone foundation . Photos: Lee H. Nelson, FAIA. 

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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 the 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 (Fig. 5). 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 of the 

outer surface to spall off or delaminate. If the mortar does 

not permit moisture or moisture vapor to migrate out of 

the wall and evaporate, the result 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. 

Figure 5. The use of hard, portland-cement mortar that is less permeable than 

the soft bricks has resulted in severe damage to this brick wall. Moisture 

trapped in the wall was unable to evaporate through the mortar which is 

intended to be sacrificial, and thus protect the bricks. As a result the moisture 

remained in the walls until water pressure eventually popped the surface off 

the bricks. Photo: National Park Service Files. 

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 dolomiticdifferentiated 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. 
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 repainting 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 becomesand 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 

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-chetnical 

method called acid digestion, whereby a sample of 

the mortar is crushed and then mixed with a dilute 

acid. The acid dissolves all the carbonatecontaining 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 carbonate 

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 "rest Method 

for Examination and Analysis of Hardened 

Mortars" which was designed specifically for the 

analysis of modem 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 modem 

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. 

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Figure 6. Tinted mortar. (lefOBlack mortar with a beaded joint was used here on this late-19th centun) hard pressed red brick and, (center) a dark brown tintedmortar 

with an almost flush joint was used on this early-20th century Roman brick. (right) When constructed at the turn-of-the-century, thIs buz/dlng was pOinted wllh a 

dark gray mortar to blend with the color of the stone, but the light-colored mortar used In spot repainting has destroyed thIs harmony and adversely Impacts the 

building's historic character. Photos: Anne Grimmer. 

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, .the~ 

produce high strength mortars that can damage histonc 

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 conta~g sand ~ay 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--dean and free from 

acids, alkalis, or other dissolved organic materials. 

Other Components 

Histodc 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 "?irty lim~", shell. 

(which often provided a source of hme, 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 f,?r each p~oject. If 

possible, suggested sources for speCIal matenals 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 ~ the late 

19th century, were tinted to match or contra~t WIt~ the 

brick or stone (Fig. 6). 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. 

Modem components. Admixtures are used to create 

specific characteristics in mortar, and ,:,h~t~er 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 retarders help 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 .~eces.sary 

and may, in fact, have detrimental effects In histonc 

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-entrainme2t of 10-16 percent may b;, . 

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 ~nd 

the adjacent surfaces. In addition, a bonding agent I~ 

difficult to remove if smeared on a masonry surface (FIg. 7). 
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. 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 0,800 psi), 

Type N (750 psi), Type 0 (350 psi) and Type K (75 psi). 

(The letters identifying the types are from the words 

MA20N 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: cementlime-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. 

Figure 7. The dark stain on 

either side of the vertical 

joint on this sandstone 

watertable probably resulted 

from the use of a bonding 

agent that was not properly 

cleaned off the masonry 

after repainting. Photo: 

Anne Grimmer. 

Figure 8. Due to inadequate joint preparation, the repainting mortar has not 

adhered properly and is fa lling out of the joint. Photo: Robert C. Mack, FAIA. 

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 that 

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. 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 

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Incorrect 

Mortar not cleaned out to a 

sufficient unifonn depth 

Edges of brick damaged by tool or 

grinder. Creates wider joint 

Correct 

Mortar cleaned out to a 

uniform depth-about I" deep. 

~~,.,.""".,..,~'" ~ Undamaged edges of brick. 

Figure 9. Comparison of incorrect and correct preparation of mortar joints 

for repointing. Drawing: Robert C. Mack, FAlA, and David W. Look, AlA. 

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. 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 locationspreferably 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. If cleaning tests, for 

Figure 10. Using a hammer and masonry chisel is the least damaging and, 

thus, generally the preferred method of removing old mortar in preparation 

for repointing historic masonry. Photo: John P. Speweik. 
Figure 11. The damage to the edges and corners of these historic bricks was 

caused by using a mechanical grinder to rake out the joints. Note the 

overcutting of the head joint and the damage to the arises (corners) of the 

bricks. Photo: Lee H. Nelson, FAIA. 

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" (Fig. 8). For most brick joints, this will 

require removal of the mortar to a depth of approximately 1/2 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 (Fig. 9). 

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 

(Fig. 10). 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 (Fig. 11). 

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. 

Figure 12 .. A power grinder, operated correctly by a skilled mason may be 

used in preparation for repainting to cut wide, horizontal mortar joints, 

typical of many early-20th century brick structures without causing damage 

to the brick. Note the use of protective safety equipment. Photo: Robert C. 

Mack, FAIA. 

Under certain circumstances, thin diamond-bladed 

grinders may be used to cut out horizontal joints only on 

hard portland cement mortar common to most early-20th 

century masonry buildings (Fig. 12). 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 

repainting. 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 (Fig. 13). Although mechanical tools may 

be used safely 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 

9 
10 

Figure 13. (left) In preparation for repointing, the mortar joints on these 

granite steps are first cut out mechanically (note the vacuum attached to the 

cutting tool in foreground to cut down on dust). (right) Final removal of the 

old mortar is done by hand to avoid damage to the edges of the joints. 

Mechanical preparation of horizontal joints by an experienced mason may 

sometimes be acceptable, especially where the joints are quite wide and the 

masonry is a very hard stone. Photos: Anne Grimmer. 

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 (Fig. 14). 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 I 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 rep ointing 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 00:2:9) or Type K 0:3:11)-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 1 Ij2 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 Ij4 inch of 

mortar, packing it well into the back corners. This 
a b c 

d e f 

Figure 14. Mixing mortar using lime putty: (a) proportioning sand; (b) proportioning lime putty; (c) placing lime putty on top of sand; (d) mixing sand over 

lime putty; (e) hand mixing mortar; and, (f) sample of mortar after mixing. Photos: John P. Speweik. 

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 (Fig. 15). 

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 (Fig. 16). 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 highlime content mortars-those mortars that contain more 

lime by volume than portland cement, i.e., Type 00:2:9), 

Type K 0:3:11), 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. 

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 

11 
12 

Figure 15. The profile of the repointed joints on the left replicate the historic 

joints around the corner to the right on the front of this stone building in 

Leesburg, VA. The contractor's pride in the repointing work is evident by the 

signature in the vertical joint. Photo: Anne Grimmer. 

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 0-2 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 

Joints 

filled 

too full 

Wide 

feather edge 

susceptible to 

spalling 

Joints 

slightly 

recessed 

Figure 16. Comparison of visual effect of full mortar joints vs. slightly recessed 

joints. Filling joints too full hides the actual joint thickness and changes the 

character of the original brickwork. Drawing: Robert C. Mack, FAlA. 

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 

Figure 17. This photograph shows the significant visual change to the 

character of this historic brick building that has resulted from improper 

repointing procedures and a noticeably increased thickness of the mortar 

joints. Photo: Lee H. Nelson, FAlA. 
Mortar Types 

(Measured by volume) 

Designation Cement Hydrated Lime Sand 

or Lime Putty 

M 1 '/4 3 - 3 3/4 

S 1 '/2 4 - 4 'Iz 

N 1 1 5-6 

0 1 2 8-9 

K 1 3 10 -12 

'1..." 0 1 2'/4 - 3 

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 Grouting is 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 Ibrick 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 infonnation on masonry cleaning is presented in 

Preseroation Briefs 1: The Cleaning and Waterproof Coating of Masonry 

Buildings, Robert C Mack, AlA, Washington, D.C: Technical 

Preservation Services, National Park Service, U.s. Department of the 

Interior, 1975; 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. 

Suggested Mortar Types for Different Exposures 

Exposure 

Masonry Material Sheltered Moderate Severe 

Very Durable: 

granite, hard-cored 

brick, etc. 0 N S 

Moderately Durable: 

limestone, durable stone, 

molded brick K 0 N 

Minimally Durable: 

soft hand-made brick "L" K 0 

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 modem 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. 
14 

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 lO-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 Reading at 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 

Figure 19. Mortar joints of 18th century brick buildings were often as much 

as 1/2 inch wide, cut flush and struck with a grapevine joint, but for window 

and door surrounds where a finer quality rubbed brick was used, mortar 

joints were very thin. Photo: National Park Service Files. 

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 (Fig. 18). 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 (Fig. 19). 

Tuckpointing is not true repointing but the 

Figure 20. This stone garden wall was tuckpointed to match the tuckpointing 

on the c. 19205 house on the property. Photo: Anne Grimmer. 
• • 

I.. 

b 

a 

e 

application of a raised joint or lime putty joint on top 

of flush mortar joints (Fig. 20). Penciling is 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, particula~ly with 

hand-made brick or rough-cut, locally-quarned 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 temperatu~e of 

approximately 70 degrees F for about a ,:"eek, ~r It can 

be baked in an oven to speed up the cunng; thIS 

sample is then broken open and the surface is compared 

Figure 18. A cross-section of mortar joint Iypes. (a). 

Grapevine joints on a mid-18th century brzck bUlldzng; 

(b) flush joints on a mid-to-late 19th century brzck . 

building; (c) beaded joints on a late-19th century brzck 

building; (d) early-20th century beaded Joznts on rou~hcut limestone where the vertical joints were struck przor 

to the horizontal joints; (e) raked joints on 1920s wire 

brick; (f) horizontal joints on a 1934 building designed 

by Frank Lloyd Wright were raked back from the face of 

the bricks, and the vertical joints were filled wIth a redtinted mortar to emphasize the horizontalily of the 

narrow bricks, and struck flush with the face of the 

bricks; (g) the joints on this 20th century glazed terracotta tile building are raked slightly, emphasizing the 

glazed block face. Photos: National Park Service Files 

(a,b,e); Robert C. Mack, FAlA (c,d,f,g). 

g 

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. 

! 

j 

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 sho.uld 

include an estimated price for the replacement matenals 

with the final price based on the actual cost to the contractor. 

15 
16 

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 (Fig. 17). The mortar 

joint in a historic masonry building has often been 

called a wall's "first line of defense." Good rep ointing 

practices guarantee the long life of the mortar joint, the 

wall, and the historic structure. Although careful 

maintenance will help preserve the freshly repainted 

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., AlA. Masonry Repainting of TwentiethCentury 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 1., AlA, 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. 46-5l. 

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."llE 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 

Portland Cement Association 

5420 Old Orchard Road 

Skokie, IL 60077 

Acknowledgments 

National Lime Association 

200 N. Glebe Road, Suite 800 

Arlington, VA 22203 

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, Repainting 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. 

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. Comments about this publication should be directed to 

de Teel Patterson Tiller, Chief, Heritage Preservation Services Program, 

National Park Service, 1849 C Street, N. W. Suite NC200, Washington, 

D.C. 20240. This publication is not copyrighted and can be reproduced 

without penalty. Normal procedures for credit to the authors and the 

National Park Service are appreciated. 

Front Cover: Repainting a historic brick building using a lime-based mortar. 

Traditional lime mortars have a consistency that enables the mortar to cling 

to a repainting tool while in a vertical position. Photo: John P. Speweik. 

ISSN:0885-7016 October 1998