HomeMy Public PortalAbout05-12-2022 HPC Minutes Meeting of the Historic Preservation Commission
Record of Minutes
Date: May 12, 2022 Location: Village Hall
CALL TO ORDER, ROLL CALL, PLEDGE
Chairman Bortel called the meeting to order at 7:04 p.m.
Roll call: Commissioners Barvian, Derrick, Hagen, Olsen, Schmidt, and Chairman Bortel were present.
Commissioner Rapp was absent.
Also, in attendance: Jonathan Proulx, Director of Planning
Chairman Bortel led the pledge to the flag.
APPROVAL OF AGENDA
Commissioner Derrick made a motion to approve the agenda. Seconded by Commissioner Olsen. Voice
Vote. All in favor. 0 opposed. Motion carried 6-0.
APPROVAL OF MINUTES
Commissioner Derrick made a motion to approve the Special Historic Preservation Commission minutes
dated March 24, as amended. Seconded by Commissioner Olsen. Vote by roll call: Barvian, yes; Hagen,
yes; Schmidt, yes; Olsen, yes; Derrick, yes; and Bortel, yes. Motion carried 6-0.
CHAIR’S COMMENTS
Chairman Bortel announced Lisa with Landmark Illinois is leaving after working there for roughly 23
years and he also stated the Alliance of Preservation is looking for a host for their meeting in the fall and
he volunteered Plainfield to host. Chairman Bortel stated he would like to have a CAMP next year.
Chairman Bortel announced there is an ordinance to be approved by the Village Board on Monday that
will reduce the Historic Preservation Commission from nine member to seven members.
Chairman Bortel remined the commission that the HPC presentation to the Village Board will be May
23rd at 7:00 p.m.
COMMISSIONERS COMMENTS
Commissioner Olsen suggested an alliance with the HPC, Park District, Will County, and the Township
for the Springbank/Old Renwick Road bridge to maintain and incorporate it into the bike path. Chairman
Bortel stated landmarking the bridge would need to be done by Will County since it is unincorporated.
Chairman Bortel stated he believes that there was at one time a plaque near the bridge marking Walker’s
Grove. Commissioner Schmidt stated he did some drawing for the bridge at the request of Larry Kachel.
Commissioner Derrick asked who they can contact at the township regarding the bridge. Mr. Proulx
stated the Road Commissioner, and he thinks an alliance is a great approach. Chairman Bortel asked staff
if the village would have interest in incorporating the bridge. Mr. Proulx indicated the village would need
to evaluate it.
PUBLIC COMMENT
No Public Comments.
Historic Preservation Commission Minutes
May 12, 2022
Page 2 of 4
OLD BUSINESS
No Old Business.
NEW BUSINESS
1966-041122.HPC 15135 S. DES PLAINES ST. NICOLE SOLIS
Commissioner Derrick made a motion to continue the public hearing for landmark designation for the
property located at 15135 S. Des Plaines Street to the June 9, 2022 Historic Preservation Commission
meeting.
Seconded by Commissioner Schmidt. Vote by roll call: Barvian, yes; Derrick, yes; Hagen, yes; Olsen,
yes; Schmidt, yes; and Bortel, yes. Motion carried 6-0.
1971-040122.COA 15126 S FOX RIVER ST. CHRIS & MARGARET
PTACEK
Mr. Proulx stated the applicant is proposing to restore two window openings that had been bricked closed,
as well as complete tuckpointing, for the property at 15126 S. Fox River St. Known as the “Hartong-
Smith House”, the home is the first property in the Village of Plainfield to receive local landmark status.
The applicant is requesting approval of Certificate of Appropriateness (COA) as well as approval of a
historic rehabilitation grant in the amount of $1,550 representing 50 percent of the total project costs of
$3,100.
Mr. Proulx reviewed the staff report dated May 10, 2022. Mr. Proulx concluded in advance of any public
comment or discussion by the Historic Preservation Commission, staff supports the proposed Certificate
of Appropriateness and rehabilitation grant requests.
Chairman Bortel swore in Margaret Ptacek, applicant. Chairman Bortel asked if they discovered it when
they were doing interior work to the home. Ms. Ptacek explained how they discovered the windows. Ms.
Ptacek stated they will be adding limestone sills to match existing windowsills of the house. Ms. Ptacek
explained the interior renovations they have made to the house.
Commissioner Derrick asked if the windows will be replaced or are they just revealing the original
windows. Ms. Ptacek confirmed they are revealing the original windows and added they will be adding
exterior storm windows. Commissioner Derrick asked if the panes in the window are vertical. Ms.
Ptacek confirmed.
Commissioner Derrick asked if the mason provide information about the removable method of the
existing mortar. Ms. Ptacek stated that was not specifically discussed with the mason, but it was
discussed that he will use historically appropriate mortar mix. Commissioner Derrick had a Preservation
Briefs regarding Repointing Mortar Joints in Historic Masonry Buildings, she would like to be attached
the Letter of Agreement (see attached). Commissioner Derrick wants to make sure the following are met
regarding the mortar work being completed:
• The removable technique of the mortar does not damage any of the bricks.
• The mortar formula to match the existing mortar.
• The mortar color needs to match existing mortar.
• The tooling of the new mortar work should match the old in depth and profile.
• The texture of the new mortar needs to match the existing grading of sand in the historic mortar.
• Asked the applicant to provide a picture of a sample or having the HPC Chairman come to the
property to confirm color match.
Historic Preservation Commission Minutes
May 12, 2022
Page 3 of 4
Commissioner Derrick indicated if the mason has any concerns about meeting the terms of the Letter of
Agreement or questions, please let the HPC know and for them to not move forward. Ms. Ptacek stated
the mason advertised that he worked on historic homes and has a portfolio to support it. Commissioner
Derrick stated the HPC is here to help owners of historic homes.
Commissioner Olsen asked where the applicant found the mason. Ms. Ptacek stated by an internet search.
Commissioner Schmidt stated the quote states they will be replacing the steel lintel but feels if the
window is still there the lintel should be. Ms. Ptacek stated they had a hard time confirming if one of the
lintels was still there and are hoping it was just mortared over. Chairman Bortel asked where the
applicant got the original picture. Ms. Ptacek stated the Historical Society.
Commissioner Schmidt made a motion to recommend approval of the requested Certificate of
Appropriateness for restoration of windows on the south elevation and tuckpointing of the local landmark
at 15126 S. Fox River St., subject to execution of a Letter of Agreement with the HPC, applicant, and
Village staff to accept the following conditions of approval:
1. Existing Windows – to be restored;
2. Limestone Sills – Replacement sills will be the same depth relative to the wall plane as the
existing windows, and the dimensions of the sills will match as best as possible to the other
existing windows;
3. Repointing Work - The removal technique of the mortar must not damage any adjacent masonry
units; the mortar formula type N or softer; mortar color needs to match existing mortar, preferably
through the use of matching aggregate to the historic aggregate versus dyes; tooling of the new
mortar work should match the old in depth and profile; texture of the new mortar needs to match
the existing grading, again preferably through the use of matching the aggregate composition and
grading;
4. Approval of a test sample of the mortar color, texture, and tooling by staff and HPC
representative before the applicant can proceed with the project; and
5. Compliance with the relevant guidance in the attached Preservation Brief regarding Repointing
Mortar Joints in Historic Masonry Buildings dated October 1998 published by the U.S.
Department of the Interior National Park Services Cultural Resources Heritage Preservation
Services is requested.
Seconded by Commissioner Barvian. Vote by roll call: Derrick, yes; Hagen, yes; Olsen, yes; Barvian,
yes; Schmidt, yes; and Bortel, yes. Motion carried 6-0.
Commissioner Derrick motion to recommend approval of the historic rehabilitation grant for restoration
of existing windows on the south elevation and tuckpointing of the local landmark at 15126 S. Fox River
St., subject to the conditions in the staff report.
Seconded by Commissioner Olsen. Vote by roll call: Barvian, yes; Hagen, yes; Schmidt, yes; Olsen, yes;
Derrick, yes; and Bortel, yes. Motion carried 6-0.
HISTORIC PRESERVATION COMMISSION ANNUAL REPORT
Commissioner Derrick made a motion to approve the Historic Preservation Commission 2021-2022
Annual Report.
Seconded by Commissioner Barvian. Vote by roll call: Hagen, yes; Olsen, yes; Schmidt, yes; Barvian,
yes; Derrick, yes; and Bortel, yes. Motion carried 6-0.
Historic Preservation Commission Minutes
May 12, 2022
Page 4 of 4
DISCUSSION
No Discussion
ADJOURN
Commissioner Derrick made a motion to adjourn. Commissioner Olsen seconded the motion.
Motion carried 6-0.
Meeting adjourned at 7:44 p.m.
Respectfully submitted,
Tracey Erickson
Recording Secretary
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 cent ury limeston e 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 exposure
should 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 leakin g downspout . Th e downspout must be replaced and any
other drainage problems repaired before repainting. Photo: Robert C. Mack ,
FAlA.
prepare specifications which reflect the particular require
ments 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. Richard son's Glessner House in Chicago (right). Photos: Charles E. Fish er: 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) Th e 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 . Th e use of hard , portland-cement mortar that is less perm eable than
the soft bricks ha s res ulted in severe dama ge to thi s brick wall. Mois ture
trapped in the wall was unable to evaporate throu gh the mortar which is
intended to be sacrificial , and thu s protec t the bricks. As a res ult the moisture
remained in the walls until water press ure eventually popped the surface off
the bricks. Photo: Na tional 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 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.
Lime, itself, w h en 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 hyd roxide) hardens by carbonation absorbing
carbon diox ide primarily from the air, converting itself to
calcium carbo n ate. Once a lime and sand mortar is
mixed and placed in a wall, it begins the process of
carbona tion. If lime mort ar 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. Th is machine-slaked lime is designed to
assure high p lasticity 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 p utty. 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 p roperty or proportion specification.
Portlan d 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 with out 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
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 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 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 char
acteristics 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 specifi
cations, 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
exa ctly 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 b y ASTM to distinguish hig h
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 p si) 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,
exce pt 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-sa nd. Thus, a Type K mix, for example, would b e
referred to as 1-3-10, or 1 part cement to 3 parts lime to
10 parts sand . Other requirements to create the desired
vis ual qualities should be included in the specification s.
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 join t preparation , the repainting mortar ha s not
adhered properly and is fa llin g 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
7
8
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 knowledge
able 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. 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 th e
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 approximate
ly 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 rem ova l of th e
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 th e
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," jeopardiz
ing 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. Mixin g mortar using lime putty: (a) proportioning sand; (b) proportioning lime putty; (c) placing lime putty on top of sand; (d) mixing sand over
lim e putty; (e) hand mixi ng morta r; and , (f) sample of mortar aft er mixing. Photo s: 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 high
lime 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 supple
mented 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 adminis
trator 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 deteriora
tion. 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~h
cut limeston e 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 red
tinted mortar to emphasize the horizontalily of the
narrow bricks , and struck flush with the face of the
bricks; (g) th e joints on this 20th century glazed terra
cotta 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 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 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 profes
sional 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