Historic Preservation - Technical Procedures
- Repointing Terra Cotta
- Procedure code:
- National Capitol Region Specifications - Agriculture Bldg
- Terra Cotta Unit Masonry
- Last Modified:
- Repointing Terra Cotta
- Last Modified:
REPOINTING TERRA COTTA
A. This procedure includes guidance on repointing terra
cotta units where the mortar is deterior= ated or missing.
B. This procedure should be used in conjunction with 04520-
02-R, which describes in more detail the purpose of
repointing in general, the materials required and
precautions that should be taken.
C. See 01100-07-S for general project guidelines to be
reviewed along with this procedure. These guidelines
cover the following sections:
1. Safety Precautions
2. Historic Structures Precaution= s
4. Quality Assurance
5. Delivery, Storage and Handling=
6. Project/Site Conditions
7. Sequencing and Scheduling
8. General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing
this procedure and should be followed, when applicable,
along with recommendations from the Regional Historic
Preservation Officer (RHPO).
A. American Society for Testing and Materials (ASTM)
A. Product Data: Submit manufacturer's technical data for
each product indicated including recomme= ndations for
their application and use. Include test reports and
certifications substantiating that produ= cts comply with
B. Restoration Program: Submit written program for each
phase of restoration process including protection of
surrounding materials on building and site during
operations. Describe in detail materials, methods and
equipment to be used for each phase of restoration work.
C. Protection Program: Submit for approval methods for
protecting windows, light fixtures, decorative metal
work, plantings, cars and landscape elements.
D. Samples: Submit, for verification purposes, prior to
mock-up erection, samples of the mortar for pointing and
masonry rebuilding and repair, in forms of 6" long by 1/2 inch
wide sample strips of mortar set in aluminum or plastic
1.04 QUALITY ASSURANCE
1. Work must be performed by a firm having not less
than five years successful experience in comparable
masonry restoration proje= cts and employing
personnel skilled in the restoration processes and
2. All technicians planned for use on the job will be
required to successfully complete five linear feet
of cutting and raking of mortar joints by hand in
the presence of the Contracting Officer prior to
working on the job. Unsuccessful performance in
this test area will be grounds for rejection of
this technician for this job.
B. Field Samples: Prior to start of general masonry restoration, prepare the following sample panels on
building where directed by Contracting Officer. Obtain
Contracting Officer's acceptance of visual qualities
before proceeding with the work. Retain acceptable panels
in undisturbed condition, suitable designated during
construction as a standard for judging completed work.
1. Repointing: Prepare two separate sample areas of
approximately 3' high by 6' wide for each type of
repointing required, one for demonstrating methods
and quality of materials and workmanship expected
in removal of mortar joints, and the other for
demonstrating quality of materials and workmanship
expected in pointing mortar joints.
C. Mock-ups: Raking and Repointing Sample Work:
1. Test/Sample Area and RHPO Approval:
a. Initially perform sample joint raking and
repointing on each of a 100 sq. ft. test of
terra cotta areas as approved by RHPO.
b. Demonstrate proficiency with joint raking
tools and ability to not damage masonry units
with hand tools.
c. Mix and cure test batch of repointing mortar
and place in joints; repeat test mix until
mortar color is approved. Test mortar should
be matched, dried and approved before placing
in joints. Sample joints should match the
historic in composition, color texture,
tooling width and other visual properties.
d. Demonstrate workmanship of repointing
procedures and joint finishing.
e. Gain written approval from RHPO for test area
before proceeding with remaining work.
2. Joint Raking Method: Rake joints by hand ONLY
using special joint cleaning chisels and hammer.
3. Repointing Method: Repoint joints by hand ONLY
using approved pointing trowels. NO "BAGGING" OR
CAULKING GUN POINTING METHODS APPROVED.
D. Source of Materials: Obtain materials for masonry restoration from a single source for each type of
material required to ensure match of quality, color,
pattern and texture.
1.05 DELIVERY, STORAGE AND HANDLING
A. Storage and Protection:
1. Protect masonry restoration materials during
storage and construction from wetting by rain, snow
or ground water, and from staining or intermixture
with earth or other type materials.
2. Protect grout, mortar, and other materials from
deterioration by moisture and temperature. Store in
a dry location or on waterproof containers. Keep
containers tightly closed and away from open
flames. Protect liquid components from freezing.
Comply with manufacturer's recommendations for
minimum and maximum temperature requirements for
1.06 PROJECT/SITE CONDITIONS
A. Environmental Requirements: Do not repoint mortar joints
or repair masonry unless air temperatures are between
40 degress Fahrenheit (4 Celsius) and 80 degrees Fahrenheit (27 Celsius) and will remain so for at
least 48 hours after completion of work.
1.07 SEQUENCING AND SCHEDULING
A. Coordinating Work: Perform masonry restoration work in
the following sequence:
1. Provide approved protection of adjacent building
materials and features.
2. Repair existing masonry including replacing
existing masonry with new masonry materials.
3. Rake out existing mortar from deteriorated joints
to be repointed.
4. Point existing mortar joints of masonry to be
5. Clean up masonry surface as required after
A. Portland Cement: ASTM C50, Type I. For stonework and
other masonry indicated, provide non-staining white
cement complying with staining requirements of ASTM C91
for not more than 0.03% water soluble alkali.
B. Hydrated Lime: ASTM C207, Type S.
C. Aggregate for Mortar: ASTM C144, unless otherwise indicated.
1. Colored Mortar Aggregate: Natural or manufactured
sand selection to produce mortar colors to match
terra-cotta joints. Contracting Officer shall
determine exact mortar color from samples prepared
for the Contractor. Match size, texture and
gradation of existing mortar as closely as
D. Water: Clean, free of oils, acids, alkalis and organic
E. Anchors: Type and size as recommended by RHPO or if not
indicated to match existing in size and type. Fabricate
anchors from AISI type 347 stainless steel.
1. Measurement and Mixing: Measure cementitious and
aggregate material in a dry condition by volume or
equivalent weight. Do not measure by shovel. Use
known measure. Mix materials in a clean container,
by hand. See also 04100-03-S for additional
2. Mixing Pointing Mortar: Thoroughly mix cementitious
and aggregate materials together before adding any
water. Then mix again adding only enough water to
produce a damp, workable mix which will retain
its form when pressed into a ball. Maintain mortar
in this dampened condition for 1-to-2 hours. Add
remaining water in small portions until mortar of
desired consistency is reached. Use mortar within
30 minutes of final mixing; do not retemper or use
partially hardened material.
3. Colored Mortar: Produce mortar of color required by
use of selected ingredients. Do not adjust
proportions without RHPO's approval.
4. Do not use admixtures of any kind in mortar, unless
B. Mortar Proportions for Terra Cotta: One part white
Portland cement, one part lime, 6 parts mortar aggregate.
D. Joint tools
E. Plywood or steel hawk
F. Stiff fiber bristle brushes
G. Spray bottle
1. Protect persons, landscaping, motor vehicles, surrounding
surfaces of building whose masonry surfaces are
being restored, building site, and surrounding
buildings from injury resulting from masonry
2. Erect temporary protection covers over pedestrian
walkways and at points of entrance and exit for
persons and vehicles which must remain in operation
during course of masonry restoration work.
3. Contractor shall test those areaway drains, window
well drains, etc., which will be used to assure
that drains are functioning properly prior to
performing masonry restoration operations in those
areas. The Contractor shall report immediately to
the Construction Engineer the location of drains
which are found to be stopped up or blocked.
4. Prevent grout or mortar used in repointing and
repair work from staining face of surrounding
masonry and other surfaces. Remove immediately
grout and mortar in contact with exposed masonry
and other surfaces.
5. Protect sills, ledges, windows, and projections
from mortar droppings.
3.02 ERECTION, INSTALLATION, APPLICATION
A. Joint Raking:
1. Cut out mortar from deteriorated joints by hand to
depths equal to 2 times their whole width but not
less than 5/8" nor less than that required to
expose sound, unweathered mortar.
NOTE: POWER OPERATED ROTARY HAND SAWS AND GRINDERS
WILL NOT BE PERMITTED ON TERRA COTTA.
a. Use chisels with a 1 inch maximum head for
cutting out the mortar. Sharpen chisels hourly
to minimize the chipping. One (1) chip per linear
yard of cutting will be the standard of
acceptable skill, or as approved by the contracting officer.
b. Do not spall edges of masonry units or widen
joints. Replace any masonry units which become
2. Rinse masonry joint surfaces with water to remove
any dust and mortar particles. Time application of
rinsing so that, at time of pointing, excess water
has evaporated or run off, and joint surfaces are
damp but free of standing water.
B. Joint Pointing:
1. Apply first layer of jointing mortar to areas where
existing mortar was removed to depth greater than
surrounding areas. Apply in layers not greater than
3/8" until a uniform depth is formed. Compact each
layer thoroughly and allow to become thumbprint-
hard before applying next layer.
2. After joints have been filled to a uniform depth,
place remaining pointing mortar in 3 layers with
each of first and second layers filling
approximately 2/5 of joint depth and third layer
the remaining 1/5. Fully compact each layer and
allow to become thumbprint hard before applying
next layer. Take care not to spread mortar over
edges onto exposed masonry surfaces, or to
3. When mortar is thumbprint hard, tool to match
original appearance of joints, unless otherwise
indicated. Remove excess mortar from edge of joint
4. Cure mortar by maintaining in a damp condition for
not less than 72 hours.
A. After mortar has fully hardened, thoroughly clean exposed
masonry surfaces of excess mortar and foreign matter
using stiff nylon or bristle brushes and clean water,
spray applied at low pressure.
B. Use of metal scrapers or brushes will not be permitted.
C. Use of acid or alkali cleaning agents will not be
END OF SECTION