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.
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 iron 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:
- For copper/bronze stains: See 04465-02-R.
- For oil stains: See 04465-03-R.
C. Safety Precautions:
- DO NOT save unused portions of stain-removal materials.
- DO NOT store any chemicals in unmarked containers.
- EXCELLENT VENTILATION MUST BE PROVIDED WHEREVER ANY SOLVENT IS USED. USE RESPIRATORS WITH SOLVENT FILTERS.
- No use of organic solvents indoors should be allowed without substantial air movement. Use only spark-proof fans near operations involving flammable liquids.
- Provide adequate clothing and protective gear where the chemicals are indicated to be dangerous.
- 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:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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:
- 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 volume. -OR-
- 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:
- Sodium Citrate (appears like enlarged salt granules):
- a. Other chemical or common names include Citrate of soda*.
- b. Available from chemical supply house, drugstore or pharmaceutical supply distributor.
- Glycerol (C3H8O3):
- a. A sweet syrupy hygroscopic trihydroxy alcohol usually obtained by the saponification of fats and used especially as a solvent and plasticizer.
- b. Other chemical or common names include Glycerine; Glyceryl hydroxide; Glycyl alcohol; 1,2,3-propanetriol; Propenyl alcohol.
- c. Potential Hazards: FLAMMABLE.
- d. Available from chemical supply house, drug store or hardware store. -OR-
- 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:
- Glass or ceramic container for mixing the solution
- Wooden utensil for stirring the ingredients
B. Wood or plastic spatula
C. Stiff bristle brush (non-metallic)
- The use of wire brushes, steel wool, or abrasive tools for cleaning will not be permitted.
- Provide adequate wash solutions (i.e. water, soap and towels) before starting the job.
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 WASHED AWAY.
A. Scrubbing Iron Stains (for larger areas):
- Apply chemical cleaner or detergent to stained surface following manufacturer's instructions.
- Scrub the surface by hand using a stiff (non-metallic) bristle brush. Begin at the top of the stained area and work down.
- Thoroughly rinse the surface with clean, clear water and allow to dry.
- Repeat as necessary to achieve the desired level of cleanliness.
B. Poulticing Iron Stains (for small localized areas):
- Mix one part sodium citrate in six parts water, and mix with 7 parts glycerine to form a thick paste.
- Thoroughly wet the concrete surface to be treated with clean, clear water.
- 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.
- When the poultice has dried, brush or scrape it off with a wooden scraper.
- Thoroughly rinse the area with clean, clear water while scrubbing with a stiff bristle brush and allow to dry.
- 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 and clean.