Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
REMOVING AND REPLACING DETERIORATED CAST STONE BALUSTERS
A. This procedure includes guidance on the removal of
deteriorating exterior cast stone (concrete) balusters
and their replacement.
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), www.astm.org
B. American Concrete Institute (ACI), www.concrete.org
C. Cast Stone Institute, www.caststone.org
D. Architectural Precast Association, www.archprecast.org
A. Product Data: Submit specifications and other data for
cast stone, including certification that it complies with
specified requirements. Include instructions for
handling, storage, installation and protection.
B. Shop Drawings: Submit drawings showing sizes, dimensions,
sections and profiles of cast stone units, arrangement
and provisions for jointing, anchoring and fastening,
supports and other necessary details for lifting devices
and reception of other work. Indicate location of each
unit on setting drawings with number designation
corresponding to number marked on each unit.
1.04 QUALITY ASSURANCE
A. Regulatory Requirements: Provide cast stone which
complies with requirements of "Specifications for Cast
Stone" (ACI 704-44) of the American Concrete Institute;
Or "Standard Specification for Architectural Cast Stone"
(Section 04-72-00 (2011) of Cast Stone Institute;
Or "Architectural Cast Stone" (Section 04720),
Architectural Precast Association.
1. Prior to installation of stonework, provide one
sample railing with all balusters to indicate
proposed range of color, texture and workmanship to
be expected in completed work. Build mock-up at
site as directed, using stone, anchors and
jointing, as specified in accordance with final
2. Obtain Contracting Officer's acceptance of visual
qualities of balusters before start of stonework.
Replace unsatisfactory mock-up work as directed,
until acceptable to Contracting Officer. Retain
sample panels during construction as a standard for
judging completed stonework. Do not alter, move or
destroy mock-up until work is completed.
1.05 DELIVERY, STORAGE AND HANDLING
A. Packing and Shipping:
1. Finished cast stone shall be carefully packed and
loaded for shipment using all reasonable and
customary precautions against damage in transit. No
material which may cause staining or discoloration
shall be used for blocking or packing.
2. Protect cast stone during storage and construction
against moisture, soiling, staining and physical
3. Handle stone to prevent chipping, breakage, soiling
or other damage. Do not use pinch or wrecking bars
without protecting edges of stone with wood or
other rigid materials. Lift with wide-belt type
slings wherever possible. Do not use wire rope or
ropes containing tar or other substances which
might cause staining.
B. Storage and Protection: Store stone on wood skids or
pallets, covered with non-staining, waterproof membrane.
Place and stack skids and stones to distribute weight
evenly and to prevent breakage or cracking of stones.
Protect stored stone from weather with waterproof, non-
staining coverings or enclosures, but allow air to
circulate around stones.
1.06 PROJECT/SITE CONDITIONS
A. Existing Conditions: Do not set cast stone in
temperatures 40 F or below.
1.07 SEQUENCING AND SCHEDULING
A. Coordinating Work: Installer must review installation
procedures and coordination with other work, with
Contractor, and other contractors and subcontractors
whose work will be affected by stonework.
See "References, 1.02" and consult industry groups (1.02 - B, C, and D)
for membership directories.
A. Cast Stone:
1. Cast stone shall be a building stone manufactured
from Portland cement concrete, precast, and of the
same composition throughout the piece.
2. Cement and aggregates shall be carefully chosen to
produce a cast stone equal in color and texture to
the appearance of the existing stone. Match only
cleaned samples of the existing stone.
3. All added colors shall be mineral oxide pigments
guaranteed by the manufacturer to be sun-fast and
4. Finish shall duplicate in all respects the finish
of specific example(s) of the existing cast stone
as designated by the Contracting Officer.
5. Aggregates shall be of known durability and shall
be proportioned to produce maximum density.
6. Before delivery, cast stone shall be properly cured
and shall have a minimum compressive strength of
5,000 psi and a maximum average water absorption of
7. All cast stone shall be sound and perfect. Make all
edges sharp and true. Provide continuous slots,
bevels, reglets, rebates and other features, as
C. Mortar and Grout:
1. Portland cement: ASTM C150, except complying with
the non-staining requirements of ASTM C91 for not
more than 0.03% water soluble alkali.
2. Hydrated Lime: ASTM C207, Type S.
3. Sand: ASTM C144.
4. Water: Clean and potable.
D. Stonework Accessories:
1. Anchors: Clean existing base anchors set in stone.
2. Setting Buttons: Lead or plastic buttons of the
thickness required for the joint size indicated,
and of the size required to maintain uniform joint
A. Mortar: Non-staining, cement/lime mortar, complying with
ASTM C270, Proportion Specification. Mortar color should
match adjacent historic mortar; match tooling and other
A. Surface Preparation: Clean all adjoining stone surfaces
before setting by thoroughly scrubbing with fiber
brushes, followed by a thorough drenching with clear
water. Use only mild cleaning compounds that contain no
caustic or harsh fillers or abrasives. If not thoroughly
wet at time of setting, drench or sponge stone.
3.03 ERECTION, INSTALLATION, APPLICATION
A. Measure the existing conditions prior to fabrication of
the cast stone. Match the existing placement and
B. Execute stonework by skilled mechanics, and employ
skilled stone fitters at the site to do necessary field
cutting as stone is set.
C. Set stone in accordance with drawings and final shop
drawings for stonework. Provide anchors, supports,
fasteners and other attachments shown or necessary to
secure stonework in place. Shim and adjust accessories
for proper setting of stone. Completely fill holes, slots
and other sinkages for anchors, dowels, fasteners and
supports with mortar during setting of stones.
D. Joints: Set units in full bed of mortar, unless otherwise
1. Wet stone thoroughly before setting.
2. Set stone before initial set of cement bed occurs.
Do not set stone on dry bed. Tamp and beat stone
for a complete contact between stone and setting
bed. Set and level each unit immediately. Set stone
in pattern shown with uniform joints.
3. Grout joints as soon as possible after initial set
of setting bed. Force grout into joints, and tool.
Wet joint surfaces, if dry, prior to grouting.
4. Cure grout by maintaining in a moist condition for
5. Remove grout spillage from face of stone as work
A. Clean stonework not less than six days after completion
of work, using clean water and stiff-bristle brushes. Do
not use wire brushes, acid-type cleaning agents or other
cleaning compounds with caustic or harsh fillers.