Historic Preservation - Technical Procedures
- Spot Cleaning Copper/Bronze Stains On Granite
- Procedure code:
- Us Custom House/P.O., St. Louis, Mo - Gsa/Pbs
- Last Modified:
- Spot Cleaning Copper/Bronze Stains On Granite
- Last Modified:
SPOT CLEANING COPPER/BRONZE STAINS ON GRANITE
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.
A. This procedure includes guidance on removing
copper/bronze stains from granite surfaces by scrubbing
with a chemical cleaner or detergent, or by poulticing
with a chemical solvent.
B. For guidance on spot cleaning other stains on granite,
refer to the following:
1. For iron stains: See 04465-01-R.
2. For oil stains: See 04465-03-R.
C. Safety Precautions:
1. DO NOT save unused portions of stain-removal
2. DO NOT store any chemicals in unmarked containers.
3. EXCELLENT VENTILATION MUST BE PROVIDED WHEREVER ANY
SOLVENT IS USED. USE RESPIRATORS WITH SOLVENT
4. No use of organic solvents indoors should be
allowed without substantial air movement. Use only
spark-proof fans near operations involving
5. Provide adequate clothing and protective gear where
the chemicals are indicated to be dangerous.
6. Have available antidote and accident treatment
chemicals where noted.
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).
E. For general information on the characteristics, uses and
problems associated with granite, see 04465-01-S.
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. For Scrubbing by Hand:
1. Chemical Cleaning Compound: Hydrofluoric (HF) and
phosphoric (H3PO4) acids in concentrations not
exceeding 5% weight to volume, with surfactants
such as ethoxylated alkylphenols and ethoxylated
alcohols at concentration of 1 to 2% weight to
2. Cleaning Detergent: Cleaning detergent designed
for use on masonry surfaces, free of deleterious
amounts of acids, alkalies and organic materials,
as recommended by manufacturer for masonry surfaces
of work to be cleaned as acceptable.
B. For Poulticing:
CAUTION: DO NOT MIX AMMONIA WITH CHLORINE BLEACHES, A
POISONOUS GAS WILL RESULT! DO NOT USE BLEACH ON BIRD
1. Ammonium Chloride - salt-like substance (NH4Cl):
CAUTION: DO NOT USE AMMONIA IN CONTACT WITH BIRD
a. A white crystalline volatile salt that is used
in dry cells and as an expectorant.:
b. Other chemical or common names include
Ammonium hydrochloride; Chloride of Ammonia*;
Hydrochloride of Ammonia*; Muriate of
Ammonia*; Sal Ammoniac*.
c. Potential hazards: TOXIC; CORROSIVE TO FLESH;
CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS.
d. Available from chemical supply house, dry
cleaning supply distributor, drugstore or
pharmaceutical supply distributor, or hardware
2. Ammonium Hydroxide (NH5O):
a. A weakly basic compound that is formed when
ammonia dissolves in water and that exists
only in solution.
b. Other chemical or common names include Ammonia
water*; Aqua ammonia*; Household ammonia*.
c. Potential hazards: TOXIC; MAY IRRITATE THE
d. Available from chemical supply house, grocery
store or pharmaceutical supply distributor, or
3. Powdered talc
4. Proprietary preparations of paste are also
available and should be used according to their
manufacturer's published instructions.
C. Clean, potable water
A. For Poulticing:
1. Glass or ceramic container for mixing the solution
2. Wooden utensil for stirring the ingredients
B. Wood or plastic spatula
C. Stiff bristle brush (non-metallic)
1. The use of wire brushes, steel wool, or abrasive
tools for cleaning will not be permitted.
2. Provide adequate wash solutions (i.e. water, soap
and towels) before starting the job.
3.02 ERECTION, INSTALLATION, APPLICATION
NOTE: DO NOT TRY MORE THAN ONE TREATMENT ON A GIVEN AREA
UNLESS THE CHEMICALS USED FROM PRIOR TREATMENT HAVE BEEN
NOTE: DO NOT USE BLEACH ON DARK COLORED STONES AS THIS WILL
CAUSE THE STONE TO LIGHTEN.
CAUTION: DO NOT MIX BLEACH AND AMMONIA. THIS WILL PRODUCE A
A. Scrubbing Copper/Bronze Stains:
1. Apply chemical cleaner or detergent to stained
surface following manufacturer's instructions.
2. Scrub the surface by hand using a stiff (non-
metallic) bristle brush. Begin at the top of the
stained area and work down.
3. Thoroughly rinse the surface with clean, clear
water and allow to dry.
4. Repeat as necessary to achieve the desired level of
B. Poulticing Copper/Bronze Stains:
1. Mix one part ammonium chloride dry with four parts
powdered talc. Add a mild solution of ammonia
(ammonium hydroxide) to form a thick paste.
2. Thoroughly wet the concrete surface to be treated
with clean, clear water.
3. Apply the mixture to the stained area using a wood
or plastic spatula and allow to dry. Be sure to
spread the poultice well beyond the stained area.
The liquid portion of the paste will migrate into
the concrete where it will dissolve some of the
staining material. Then the liquid will gradually
move back beyond the concrete surface and into the
poultice, where it will evaporate, leaving the
dissolved staining material in the poultice.
4. When the poultice has dried, brush or scrape it off
with a wooden scraper.
5. Thoroughly rinse the area with clean, clear water
while scrubbing with a stiff bristle brush and
allow to dry.
6. Repeat the process as necessary to achieve the
desired level of cleanliness.
NOTE: Finished work shall show no signs of stains, scratches,
streaks or runs of discoloration, mortar damage or other like
defects from use of cleaners. Leave all masonry surfaces neat
END OF SECTION