Historic Preservation - Technical Procedures
- Repointing Marble
- Procedure code:
- National Capitol Region Specifications
- Last Modified:
- Repointing Marble
- Last Modified:
A. This procedure includes guidance on raking out and
repointing the deteriorated or inappropriately repointed
horizontal and vertical joints on exterior marble.
B. 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).
A. American Society for Testing and Materials (ASTM)
1.03 QUALITY ASSURANCE
A. Regulatory Requirements: Marble Design Manual, ASTM C144-
70, Aggregate for Masonry mortar; ASTM C150-74 Portland
Cement; manufacturer's printed recommendations for
product use and installation.
B. Certifications: Prior to delivery, submit certificates
attesting compliance with applicable specifications for
grades, types, classes.
C. Field Samples: Prior to raking out all areas, cut back
joints at location selected by the 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 and
left unpointed until all other pointing is completed.
Point when directed by the Contracting Officer.
1.04 PROJECT/SITE CONDITIONS
A. Existing Conditions: No stone work will be performed when
the air temperature is 40 F and falling or when stone
surface temperature is 40 F or below.
A. Portland cement: Type I, ASTM C150, gray and/or white as
necessary to match mortar color specified.
B. Hydrated masons lime: ASTM C207.
C. Aggregate: See ASTM C144 (ASTM 1997a). Clean sharp sand free of loam, silt, soluble
salts and organic matter. Sand color should match stone color as closely as possible. Aggregate shall conform to the
size gradations specified as a result of laboratory
analysis of an approved sample.
1. Choose the color of the aggregate so that the dry
mortar color matches specified color.
D. Water: Clean and free of deleterious amounts of oils,
acids, alkalis and organic matter.
B. Joint tools
D. Stiff fiber bristle brushes
F. Rubber mallet
A. Proportions for Marble Pointing, or as determined by
1. Portland cement: 1 part by volume
2. Lime: 2 parts by volume
3. Aggregate: 9 parts by volume
4. Water: To form a workable consistency
B Mixing Procedures:
1. Measure materials by volume or equivalent height.
2. Do not measure by shovel. Use known measure.
3. Mix ingredients in clean mechanical batch mixer for
4. Let mortar sit for 20 minutes prior to use to allow
for initial shrinkage. Use mortar within 1 hour
of initial mixing.
3.01 ERECTION, INSTALLATION, APPLICATION
A. Rake out all stone joints in designated areas by hand
using a chisel no more than width of the mortar joint. 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 marble. 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 satisfaction.
B. Raked joint depth to be at least 3/4" but in all cases rake
back to expose sound mortar. Raked joint depth should be 2 to 2 1/2 times the joint width.
C. Brush, vacuum or flush joints to remove all dirt and
D. Reduce initial absorption of the stone by thoroughly
wetting (surface dry) with clean water just prior to
E. 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.
F. Use clean tools and equipment free from hardened or
partially set mortar.
G. Clean excess mortar from stone and joints, removing
splashed mortar and droppings immediately.
H. Do not retemper or use mortar which has partially set, is
caked or is lumpy.
I. Finish horizontal and vertical face joints. Do not allow
mortar to extend over the surface of the stone.
J. 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 repairing, pointing and resetting the
marble, immediately remove mortar, grout and adhesives
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 marble only with fiber bristle brushes and water.
Use no acids, detergents, or other cleaning agents.
END OF SECTION