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Resetting Loose Sandstone Units
RE-SETTING LOOSE SANDSTONE UNITS
PART 1---GENERAL
1.01 SUMMARY
A. This procedure includes guidance on re-setting loose
sandstone units. GENERALLY, THIS PROCEDURE SHOULD BE
PERFORMED BY AN EXPERIENCED CONTRACTOR.
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
3. Submittals
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).
1.02 REFERENCES
A. American Society for Testing and Materials (ASTM)
www.astm.org
1.03 QUALITY ASSURANCE
A. Standards: ASTM C144, Aggregate for Masonry Mortar; ASTM
C150, Portland Cement; ASTM C207, Hydrated Masons Lime;
and manufacturer's printed recommendations for product
use and installation.
B. Certifications: Prior to delivery, submit certificates
attesting to compliance with applicable specifications
for grades, types and classes.
C. 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 and
left unpointed until all other pointing is complete.
Point when directed by the Contracting Officer.
D. Sample Stone Pointing and Repair: Repoint joints, re-
attach stone fragments and repair stone using materials
and methods specified at a location(s) 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 and left undisturbed.
E. To obtain sand/aggregate that matches historic, have a
sample analyzed. Color and texture should be closely
matched to eliminate need for pigment additives which can
fade and reduce strength of mortar.
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 F and falling during and for 48
hours subsequent to laying.
PART 2---PRODUCTS
2.01 MATERIALS
A. Mortar for Bedding and Pointing:
1. Portland Cement: Type 1, ASTM C150, gray and/or
white mixed as necessary to match mortar color to
original mortar.
2. Hydrated Masons Lime: ASTM C207, Type S.
3. Aggregate: Clean, sharp sand free of loam, silt,
soluble salts and organic matter. Select
aggregate and pigment to match the final mortar
color to the color of the original mortar.
4. Water: Clean and free of deleterious amounts of
oil, acid, alkalis and organic matter.
2.02 EQUIPMENT
A. Brushes: Natural fiber or nylon bristle only.
B. Mixing Vessels: Polyethylene plastic or as recommended
by adhesive manufacturer.
C. Measuring Boxes
D. Joint tools
E. Chisel
F. Hammer
G. Hawk
H. Trowel
I. Putty knife
2.03 MIXES
A. Bedding Mortar Mix Proportions: Mix by Volume.
1. 1 part Portland cement
2. 2 parts lime putty
3. 10 parts sand
NOTE: DO NOT ADD PIGMENTS TO THE BEDDING MORTAR.
B. Pointing Mortar Mix Proportions (Type O): Typical for
most wall surfaces, not directly exposed to the weather.
Mix by volume the following:
1. 1 part Portland cement
2. 2 parts lime putty
3. 12 parts sand
4. Add pigments as required, but NEVER more than 10%
of the total weight of portland cement. Much
smaller amounts are usually enough. Always use the
smallest amount necessary to produce the desired
color and limit carbon black to 2%. Pigments
should be of mineral oxide composition.
C. Pointing Mortar Mix Proportions (Type N): More common for
surfaces directly exposed to the weather.
Mix by volume the following:
1. 1 part Portland cement
2. 1 part lime putty
3. 10 parts sand
4. Add pigments as required, but NEVER more than 10%
of the total weight of portland cement. Much
smaller amounts are usually enough. Always use the
smallest amount necessary to produce the desired
color and limit carbon black to 2%. Pigments
should be of mineral oxide composition.
PART 3---EXECUTION
3.01 ERECTION, INSTALLATION, APPLICATION
A. For Small Stones:
1. Carefully remove small shifted and/or loose
sandstone units. Clean of dirt, mortar, and loose
debris. Retain for re-use. Re-build support
masonry and lay new bedding material.
2. Remove loose debris from the stone cavity, and
rinse with water to remove dust.
3. Pre-wet adjacent surfaces with clean, potable
water.
4. Re-set sandstone in an evenly filled bed of mortar,
with full mortar coverage on horizontal and
vertical joints. Maximum tolerances from plumb and
level new work, not to exceed variation from plumb
and level of adjacent existing work. Match
existing placement, pattern and location. Note: If
replacement units are required, they should match
original sandstone in color, texture, and size, and
be free from salts and other contaminants.
5. Construct uniform joints. Shove vertical joints
tight. Adjust stone units to final position while
mortar is soft and plastic. Set stone with joints
tooled back 1". Point remaining depth as the rest
of the stone is pointed. See 04470-06-R for
guidance on repointing sandstone.
6. Keep mortar and stone damp (80-90% RH) for 72 hours
or until mortar is cured.
B. For Large Stones:
1. DO NOT REMOVE.
2. Tightly secure large stones using wooden wedges
soaked in water.
3. Carefully clean joints of loose mortar and other
debris and repoint in place. See 04470-06-R for
guidance on repointing sandstone.
3.02 ADJUSTING/CLEANING
A. At the time of repairing, patching, pointing and re-
setting of the stone, immediately remove mortar, grout
and adhesives from the face of the masonry.
B. Clean stone only with fiber bristle brushes and water.
Use no acids, detergents or other cleaning agents.
END OF SECTION
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