Historic Preservation - Technical Procedures
- Pointing Granite And Filling Cracks
- Procedure code:
- National Capitol Region Specifications - Customs Svc Bldg
- Last Modified:
- Pointing Granite And Filling Cracks
- Last Modified:
POINTING GRANITE AND FILLING CRACKS<= br>
A. This procedure includes guidance on pointing deteriorated
joints on vertical granite surfaces. The procedure
described may also be used to fill minor cracks in
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), www.astm.org
1.03 QUALITY ASSURANCE
A. Certificates: Prior to delivery, submit certificat= es
attesting to compliance with applicable specifications
for grades, types and classes.
B. Joint Raking: Prior to raking out all areas, cut back
joints at location selected by Contracting Officer using
the methods specified. Raking will continue at no
additional cost to the Government, until an acceptable
sample is achieved. This area will serve as standard for
joint raking for the entire job. It will be marked with
masking tape and left unpointed until all other pointing
is complete. Point when directed by the Contracting
C. Sample Stone Pointing: Repoint joints, using materials
and methods specified at a location selected by the
Contracting Officer. The samples accepted by the
Contracting Officer will serve as a standard for the
entire job. They will be marked with tape and left
undisturbed. Pointing mortar should match historic in
appearance, strength and composition.
1.04 PROJECT/SITE CONDITIONS
A. Environmental Requirements: No stone pointing or repair
shall be performed when the air temperature or stone
surface temperature is 40 degrees F, and falling during and for
48 hours subsequent to laying.
A. Mortar For Granite Pointing: Follow manufacturer's=
printed recommendations for product use and installation.
1. Portland Cement: Type 1, ASTM C150, gray or white as
required to match existing color.
2. Hydrated Masons Lime: ASTM C207, Type S.
3. Aggregate: ASTM C144; clean, sharp sand free of
loam, silt soluble salts and vegetable matter.
Aggregate shall conform to the following size
Sieve Size Percent Passing
No. 4 100
No. 8 100
No. 16 85 - 95
No. 30 40 - 60
No. 50 15 - 20
No. 100 1 - 5
4. Water: Clean and free of deleterious amounts of
oil, acid, alkalis and organic matter.
A. Proportions for Granite Pointing: Mix/proportions for
aggregate color and texture should close= ly match
1. Portland Cement: 1 part by volume.
2. Lime: 1 party by volume.
3. Aggregate: 3 parts by volume.
4. Water: to form a workable consistency.
B. Mixing Procedures: (see also 04100-03-S for additional
1. Measure materials by volume or equivalent weight.
2. Do not measure by shovel. Use known measure.
3. Mix ingredients in clean mechanical batcher for 3-5
4. Let mortar sit for 20 minutes prior to use to allow
for initial shrinkage. Use mortar within 1=AB hours
of initial mixing.
3.01 ERECTION, INSTALLATION, APPLICATION
A. Rake out all stone joints in designated areas by hand
using a chisel no wider that 3/4 (three fourths) joint width.
Remove all unrequired metal fasteners from granite and granite joints.
B. Clean all mortar from surfaces within the joint or crack
so that the new pointing mortar bonds to the building
material, not old mortar. Do not chip or spall edges of
the stone. More than one chip per square yard will be
unacceptable. If work is found unacceptable, all raking
will cease without additional cost to the Government
until deficiencies in tools, workers or methodologies
have been corrected to the Contracting Officer's
C. Joint depth to be at least 3/4", but in all cases rake
back to expose sound mortar.
D. Brush, vacuum or flush joints to remove all dirt and
E. Reduce initial absorption of the stone by thoroughly
wetting stone surface with clean water just prior to
repointing. Do not allow water to pool on surface of the
F. Pack joints with mortar leaving no voids. Place mortar in
layers not exceeding 1/4 inch in depth. Apply succeeding layers
only after preceding layer has taken initial set.
G. Use clean tools and equipment free from hardened or
partially set mortar.
H. Clean excess mortar from stone and joints, removing
splashed mortar and droppings immediately
I. Do not retemper or use mortar which has partially set, is
caked, or is lumpy.
J. Tool horizontal and vertical face joints flush, dense and
smooth after mortar has taken initial set. Do not allow
mortar to extend over the stone surface.
K. Curing: Keep joints damp (90% RH) for at least 72 hours
or until surface is cured. Protect joints from rapid
drying due to wind (i.e., covering tarps, enclosure on
A. At the time of pointing of the stone, immediately remove
mortar, grout and sealant from the face of the masonry.
B. Use only tools and equipment which are clean and free of
hardened or partially hardened material.=
C. Clean stone only with fiber bristle brushes and water.
Use no acids, detergents, or other cleaning agents.
END OF SECTION