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.
REMOVAL OF SOILING FROM SANDSTONE PRIOR TO REPOINTING
THE CLEANING OR REMOVAL OF STAINS FROM STONE MAY INVOLVE THE USE
OF LIQUIDS, DETERGENTS OR SOLVENTS WHICH MAY RUN OFF ON ADJACENT
MATERIAL, DISCOLOR THE STONE OR DRIVE THE STAINS DEEPER INTO THE
POROUS STONE. USE THE PRODUCTS AND TECHNIQUES DESCRIBED HERE ONLY
FOR THE COMBINATIONS OF DIRT/STAIN AND STONE SPECIFIED.
SOME DEGREE OF AGING, WEATHERING AND COSMETIC DEFECT IS NATURAL
AND ACCEPTABLE AND CONTRIBUTES TO THE BUILDING'S CHARACTER.
NATURAL WEAR AND WEATHERING SUCH AS DEPRESSIONS IN THE STONE MAY
NOT BE SUFFICIENT CAUSE FOR REPAIR.
A. This procedure includes guidance on removing biological
growth, surface dirt and efflorescence from sandstone
surfaces prior to repointing.
CAUTION: DO NOT CLEAN SANDSTONE FREQUENTLY. THIS MAY
CAUSE A PREMATURE BREAKDOWN OF THE BONDING AGENTS OR
CEMENTIOUS MATERIAL THAT BINDS THE STONE TOGETHER.
B. Sandstone is very porous and prone to picking up dirt,
dust, oils, and greases from both direct contact and from
the atmosphere. The absorption of these kinds of
contaminants can cause surface staining, and promote
C. Biological growths such as lichens, algae, moss and fungi
growing on stone walls is usually an indication that
there is excess moisture in or around the stone. These
growths should be removed, as they attract moisture to
the stone surface and hold it there, which can lead to
more serious problems. Lichens and mosses in particular,
produce oxalic acid which can damage certain types of
D. 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. Rohm & Haas (subsidiary of Dow Chemical)
B. Sigma-Aldrich Corporation
NOTE: Chemical products are sometimes sold under a common
name. This usually means that the substance is not as pure as
the same chemical sold under its chemical name. The grade of
purity of common name substances, however, is usually adequate
for stain removal work, and these products should be purchased
when available, as they tend to be less expensive. Common
names are indicated below by an asterisk (*).
A. Non-ionic Detergents such as "Triton" (Rohm & Haas),
"Igepal" (Sigma-Aldrich), or approved equal.
CAUTION: DO NOT MIX AMMONIA WITH CHLORINE BLEACHES, AS CHLORINE GAS,
(POISONOUS GAS) WILL RESULT! DO NOT USE BLEACH ON BIRD
1. Other chemical or common names include Bleaching
solution*; Household bleach*; Laundry bleach*; Sodium
Hypochlorite (NaOCl); Solution of chlorinated soda*.
2. Potential Hazards: CORROSIVE TO FLESH.
3. Available from chemical supply house, grocery store
or supermarket, hardware store or janitorial supply
C. Clean, potable water
A. Stiff natural bristle brush
B. Low pressure sprayer or garden hose
C. Polyethylene sheet
D. Wooden spatula or tongue depressors
A. Determine the source of excessive moisture, i.e. leaky
downspout, standing water, roof overhang, vegetation,
etc., and make any necessary repairs before continuing
with this task.
B. Determine the type of stain, i.e. algae and lichens, mold
and mildew, or efflorescence.
1. Provide adequate wash solutions (i.e. water, soap
and towels) before starting the job.
2. Do not spray in the immediate vicinity of
unprotected people, landscaping, and animals.
B. Surface Preparation: Temporarily fill large cracks with
foam backer rod before areas are cleaned to avoid the
infiltration of large amounts of water.
3.03 ERECTION, INSTALLATION, APPLICATION
CAUTION: DO NOT USE ABRASIVE CLEANING METHODS. DO NOT USE
ACIDIC OR ALKALI CHEMICAL CLEANERS. ALWAYS USE THE GENTLEST
MEANS OF CLEANING POSSIBLE.
A. For Crumbly Caulking Compound:
1. Remove the flaking caulking compound using wooden scrapers
or tongue depressors. Take care not to gouge or
damage the stone.
2. Remove as much as possible using a stiff bristle
CAUTION: DO NOT USE STEEL WIRE BRUSHES AS THEY MAY
LEAVE BEHIND BITS OF IRON, WHICH COULD RUST AND
LEAVE STAINS ON THE SURFACE. DO NOT USE POWERED
ROTARY BRUSHES. THESE ARE TOO HARSH AND MAY
SEVERELY ABRADE THE SURFACE.
3. Small amounts of residual caulking compound may
remain on the surface, and should be left alone.
DO NOT USE SOLVENTS TO REMOVE THIS RESIDUE. It is
likely that this residue will weather away
naturally and cause no physical harm to the stone.
4. Retain silicone caulking compounds which may have
been applied to help seal some flashing joints, and
make repairs if necessary.
B. For Loose Dirt and Dust, Bird Droppings:
1. Wash the surface with water using a low-pressure
sprayer or garden hose with a fine spray.
2. Gently scrub as necessary with a wet natural
bristle or plastic bristle brush.
3. If necessary, add a non-ionic detergent to the
sprayer at the lowest effective concentration.
Note: Test a small area to see that it does not
leave behind a hazy residue.
4. Avoid soaking the stone. Rinse the surface
thoroughly to prevent hazy or invisible residues
which may attract dirt.
C. For Molds, Mosses, and Algae: Fungal/algal growth is
fostered in environments high in moisture. This,
combined with lack of sunlight, creates favorable
conditions for this type of surface staining.
1. Eliminate conditions of excess moisture.
2. Carefully scrub the surface with a natural bristle
or plastic brush and water.
3. If necessary, add a small amount of bleach to the
water to help kill the plant growth.
D. For Efflorescence and Surface Salts:
1. Carefully dry-brush salts off the surface using a
natural bristle brush or wash with water.
2. If the efflorescence returns, carefully examine
surrounding areas to determine the possibility of
leaks or sources of water causing excess moisture
3. Eliminate sources of excess moisture and repeat
E. For guidance on repointing, see 04470-06-R.