U.S. General Services Administration
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.
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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 POROUS STONES. USE THE PRODUCTS AND TECHNIQUES DESCRIBED HERE ONLY FOR THE COMBINATIONS OF DIRT/STAIN AND STONE SPECIFIED.
PART 1–GENERAL
1.01 SUMMARY
A. This procedure includes guidance on treating marble which has been lightened or etched as a result of improper exposure to bleaching agents. Household bleach contains the acid Sodium Hypochlorite. All acids can be harmful to marble materials if they are not sufficiently diluted, and cleaners containing acids can be harmful to marble by etching or discoloring the surface.
B. 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
- Submittals
- 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).
C. For general information on the characteristics, uses and problems associated with marble, see 04455-01-S.
PART 2–PRODUCTS
2.01 MATERIALS
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. Oxalic Acid (COOH)2 or (H2C2O4):
- A poisonous strong acid that occurs in various plants as oxalates and is used especially as a bleaching or cleaning agent and in making dyes.
- Other chemical or common names include Dibasic acid; Ethanedioic acid; Acid of sugar*.
- Potential Hazards: TOXIC; CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS.
- Available from chemical supply house, dry cleaning supply distributor, drugstore or pharmaceutical supply distributor, hardware store, or photographic supply distributor (not camera shop). (Often sold under a manufacturer’s brand name; the chemical name may appear on the label.)
B. Linseed Oil: Available from hardware or paint store.
C. Clean, soft, white cloths
2.02 EQUIPMENT
A. Stiff fiber bristle brush
PART 3–EXECUTION
3.01 EXAMINATION
A. Examine the marble surface CAREFULLY to determine the cause of staining before proceeding with any cleaning operation.
3.02 ERECTION, INSTALLATION, APPLICATION
A. Thoroughly rinse the area with clean, clear water to remove any bleach remaining on the surface.
B. If the marble surface is etched, re-polish the area with a polishing powder such as aluminum oxide or oxalic acid. For guidance, see 04455-15-R “Removing Etch Marks in Marble” followed by 04455-02-P “Re-polishing Marble”.
C. If the area is lightened, try applying a thin application of linseed oil to the affected area. This might darken the stained area so that it is not as noticeable. NOTE: ALWAYS TEST A SMALL AREA FIRST, AND OBTAIN APPROVAL FROM RHPO BEFORE PROCEEDING WITH THE TREATMENT OF LARGER AREAS.