Historic Preservation - Technical Procedures
- Repointing Masonry Using Lime Mortar
- Procedure code:
- The Custom House/Portland, Or - Gsa/Facilities Support Ctr
- Masonry Restoration
- Last Modified:
- Repointing Masonry Using Lime Mortar
- Last Modified:
REPOINTING MASONRY USING LIME MORTAR
A. This procedure includes guidance on repointing stone
masonry using lime mortar.
B. Repointing is the process of removing deteriorated mortar
from a masonry joint and replacing old mortar with new,
C. This process is sometimes referred to as "tuck pointing",
though "tuck pointing", is actually a decorative
treatment rather than a method of repair. True tuck
pointing is the process of adding a finish layer of
mortar, occasionally tinted, to the outer portion of a
newly laid joint.
D. Major reasons for mortar joint failures include:
1. Weathering action,
3. Temperature cycles,
4. Poor original design and materials, and
5. Lack of exterior maintenance.
E. 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 Precautions
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).
F. For guidance on preparing lime mortar, see 04100-03-S.
A. Manufacturers' literature describing packaged items.
B. Source and screen analysis of bulk aggregate.
C. Mortar sample: Submit, for verification and approval,
a sample of each type of mortar used, in form of 6" long
by 1/2" wide sample strips of mortar set in aluminum or
1. Provide record of mortar mix, composition and field
procedures to be followed.
1.03 QUALITY ASSURANCE
A. 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
stone, brick, and terra cotta areas as
approved by RHPO.
b. Demonstrate proficiency with joint raking
tools and ability to not damage masonry units
with either hand or power 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
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.
1.04 PROJECT/SITE CONDITIONS
A. Environmental Conditions: Perform repointing only when
the temperature is between 40 degrees Fahrenheit and 80
degrees Fahrenheit. If the temperature is below 40
degrees, the mortar sets too slowly, and there is a good
chance of freezing before it fully sets. If the
temperature is above 80 degrees, the mortar will set too
quickly, and there is a strong chance of excessive loss
of water prior to adequate setting.
A. Repointing Tools: Available from good hardware stores,
building material suppliers or mail-order catalogues.
1. The Stanley Gold-blatt Tool Co.
2. Marshalltown Trowel Co.
A. Lime mortar (See 04100-03-S for materials and procedures
in preparing lime mortar)
B. Clean, potable water
A. Trowels: range in length from 10-12 inches
1. Joint chisels or a standard mason's chisel with a
1-1/2 in. blade and a long narrow handle
2. Floor chisels
1. 5# stone dressing hammer
2. 2# striking hammer
3. "No-Bounce" hammer
4. Full size and one half size brick hammers
D. Joint Tools: (see 2.01 MANUFACTURERS above)
1. 3/8"-1/4" raised beaded tool
2. 3/8"-1/4" beaded striking tool
3. 1/2" raised beaded tool with offset handle
4. 1/2" flat joint iron
5. Pointing tool should be about 1/16" narrower than
the joint being filled to achieve good compaction
E. Hawks: Plywood or steel hawk (mortar board)
1. Natural bristle brushes
2. Stiff bristle brushes (no wire)
G. Spray bottle
A. See 04100-03-S for lime mortar mixes
A. Examine all existing exterior mortar joints. If the
answer to any of the following questions is yes, then the
building's joints are deteriorated and need repointing:
1. Are mortar joints eroded back more than 1/4" from
the masonry face?
2. Are there cracks running vertically or horizontally
through the mortar?
3. Are mortar bonds broken or pulled away from the
4. Has mortar fallen out of joints?
5. Is mortar excessively soft, powdery or crumbling?
6. Is pointing badly-stained?
B. Typical exterior damage due to mortar deterioration
includes open joints, efflorescence, spalling and
loosened masonry units.
C. Typical interior damage due to mortar deterioration
includes failing plaster and stained wall paper.
D. A professional pointer experienced in old masonry is
required for any of the following areas or conditions:
1. Chimneys need repointing
2. Window lintels must be rebuilt
3. Masonry is loose or missing
4. Work must be done from scaffolds or extension
5. The original mortar joints were "beaded"-tooled
with a raised, round-profiled joint that projects
out from the wall
A. Preparing the Joints:
1. Clean area of loose dirt and debris using a stiff
bristle brush and remove all extraneous fastenings
2. Install necessary protection of adjacent building
materials, property and persons from joint cleaning
work and dirt.
3. Control dust and dirt from raking work; dampen area
being worked; and use curtains to limit spread of
dust from joint raking and cutting operations.
B. Joint Cutting and Raking:
1. Cut and rake old mortar from existing joints by
hand using a hammer and chisel. NOTE: POWER
CHISELS AND POWER SAWS SHOULD NOT BE USED.
2. Place the chisel in the center of the joint and
pound it with a striking hammer or "No-Bounce"
hammer until the mortar disintegrates.
3. Rake out the loose material to a depth of about 1
inch and never to a depth less than their width.
Leave a clean, square face at the back of the joint
to provide optimum contact with the new mortar.
CAUTION: AVOID OVERCUTTING ENDS OF VERTICAL
JOINTS, WIDENING JOINTS OR CUTTING INTO BEDDING
FACES OF MASONRY UNITS.
4. While raking out joints, remove all metal fittings
such as nails, brackets and clips on both
horizontal and vertical surfaces.
5. Carefully clean out the prepared face with a soft
or stiff bristle brush, or blow the joints clean
with low-pressure compressed air (40-60 psi).
6. Thoroughly flush out joint with clean, clear water.
3.03 ERECTION, INSTALLATION, APPLICATION
A. Filling Joints:
1. Dampen masonry surfaces and joints to control
suction and evaporation before placing repointing
NOTE: THERE SHOULD BE NO FREE WATER PRESENT WHICH
MAY CAUSE VOIDS IN THE MORTAR.
2. Using a pointing tool, push the mortar into the
joint from a board and iron with the maximum
possible pressure; The mortar should be applied in
layers, each to a maximum thickness of 3/8".
NOTE: THE POINTING TOOL SHOULD BE ABOUT 1/16"
NARROWER THAN THE JOINT BEING FILLED TO ACHIEVE
GOOD COMPACTION. IN SOME CASES, THE JOINTS WILL BE
SO THIN THAT A STANDARD POINTING TOOL WILL NEED TO
BE GROUND DOWN TO FIT THE JOINT.
3. Thoroughly compact each layer of mortar and allow
to set until thumb-print hard before applying the
next layer of mortar.
4. Fill the joints so that they are slightly recessed
from the masonry face. Avoid leaving a joint which
is visually wider than the actual historical
5. Continuously keep all excess and spilled mortar
brushed off the faces of masonry units, ledges and
other surfaces before it sets or stains the work.
B. Joint Finishing:
1. Begin when mortar attains "thumb print" hardness.
2. Tool the joint to match the old mortar.
NOTE: IT IS IMPORTANT TO TOOL THE JOINT AT THE
RIGHT STAGE; IF THE JOINT IS TOO SOFT, THE COLOR
WILL BE LIGHTER THAN EXPECTED AND HAIRLINE
SHRINKAGE CRACKS ARE LIKELY TO OCCUR; IF THE JOINT
IS TOO HARD WHEN TOOLED, DARK STREAKS MAY APPEAR
(TOOL BURNING) AND GOOD CLOSURE OF THE MORTAR
AGAINST THE MASONRY WILL NOT BE ACHIEVED.
EXCESSIVE TOOLING MAY BRING LIME AND FINE
AGGREGATES TO THE SURFACE, CREATING A VISUAL CHANGE
IN THE TEXTURE AND A SURFACE SUBJECT TO EARLY
3. To produce a roughened texture, lightly spray the
mortar with water after the initial set, stipple
the mortar with a stiff bristle brush or dab the
mortar with coarse sacking.
4. Protect finished work from direct sun and rain
until the face has dried and hardened.
A. Cleaning Up:
1. Use masking and drop cloths to prevent mortar
stains on adjacent work and ledges.
2. Keep work areas clean and free from mortar drips,
spills and residue of waste mortars or wash-off.
3. Clean off excess mortar as work proceeds using
masonry brushes before mortar sets.
4. Wash completed repointing work when finished mortar
joints are set with clean water and masonry
brushes, scrubbing only as required to clean mortar
stains off masonry without scouring the units and
5. Do not use acid or detergent cleaning agent to aid
mortar removal and clean-up without written
approval from RHPO.
1. Schedule work only when moderate weather is
2. Protect completed work from adverse weather, heavy
rainfall, freezing, and drying by direct sunlight
and winds until cured.
3. Sprinkle or mist repointed work as required to
achieve cure in mortar joints for a minimum of 72
hours after completion.
4. Lime Mortar: Cures by drying and crystallization,
not by hydration; and can be washed out of joints
if not protected before it cures.
C. Final Cleaning:
1. 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.
NOTE: USE OF METAL SCRAPERS OR BRUSHES IS NOT
PERMITTED. USE OF ACID OR ALKALI CLEANING AGENTS
IS NOT PERMITTED.
D. Some efflorescence, called new construction "bloom,"
occasionally appears on the surface within the first few
months following a repointing project. These deposits
normally are harmless and are removed by the natural
washing of the rain. If not removed by natural
weathering, they can be removed with dry brushing with a
bristle brush. The use of chemical cleaners to remove
this type of efflorescence normally is not necessary;
AVOID USING ACIDS, PARTICULARLY MURIATIC ACID.
END OF SECTION