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.
- This procedure includes guidance on the removal of surface dirt and environmental pollution from exterior granite.
- 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).
- For precautions relating to pressure washing, see 04510-04-S.
- Commercial masonry cleaner with a maximum 4% acid concentration, surfactants and wetting agents such as "Sure Klean Restoration Cleaner" - undiluted (ProSoCo, Inc.), or "Diedrich 101G Granite, Terracotta and Brick Cleaner" - diluted 1:4 to achieve a maximum 4% acid concentration (Diedrich Technologies, Inc.), or approved equal.
- Clean, potable water
- Pressure water rinsing equipment (measuring between 100 and 400 psi for low-pressure; between 400 and 800 psi for medium pressure).
- Fan-type spray tips (15 degree fan spray)
- Stiff bristle brushes (non-metallic)
- Plastic spatula
3.01 ERECTION, INSTALLATION, APPLICATION
NOTE: WHEN CLEANING, AVOID OVERCLEANING. AIM FOR ACHIEVING 85% CLEAN. MOST DAMAGE OCCURS WHEN ATTEMPTING TO CLEAN THE LAST 15%.
NOTE: TEST CLEAN A SMALL AREA BEFORE ATTEMPTING TO CLEAN LARGE AREAS.
NOTE: DO NOT TREAT THE SURFACE WITH ACID CLEANER MORE THAN ONCE.
- Saturate the granite with clean, warm water sprayed at a low pressure (between 100 and 400 psi). Remove bird excrement and debris from granite prior to the application of acidic granite cleaner (see 04510-02-R for guidance).
- Spray-apply cleaner evenly to the stained surface at 125 psi. or as recommended by manufacturer, or brush-apply cleaner using a soft fiber bristled brush.
- Allow cleaner to stand on the surface for 3-5 minutes or as recommended by manufacturer.
- Thoroughly rinse the surface with clean, clear water at medium pressure (between 400 and 800 psi). Nozzle should be held between 18 and 30 inches from the surface. Stone should be left clean without streaking or staining.