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.
PART 1–GENERAL
1.01 SUMMARY
- This procedure includes guidance on cleaning blackened clay roofing tiles.
- Clay tile may become discolored or blackened due to any of the following:
- Dirt build-up from air pollutants
- Organic growths such as lichen, algae or moss
- Industrial pollutants
PART 2–PRODUCTS
2.01 MATERIALS
- Household detergent, household ammonia, weed killer, or mixture of zinc or magnesium and water.
- Clean, potable water
2.02 EQUIPMENT
- Stiff bristle brush
- Ladder
- Garden sprayer/garden hose
- Medium or coarse long handled vegetable fiber brushes
PART 3–EXECUTION
3.01 PREPARATION
- Surface Preparation:
- Sweep down tile to remove dirt and debris. Use a long handle broom or brush with more rigid bristles which do not scratch the tile surface.
- Pick up and bag the debris washed from the tile such as leaves, dirt, and other litter from the gutter and clean gutter at the same time.
3.02 ERECTION, INSTALLATION, APPLICATION
- For Dirt and Pollutant Crusts: Scrub the tile by hand with water and a stiff bristle brush.
- . For Organic Growth:
- Remove growth with a stiff bristle brush and clean water.
- Apply detergent, household bleach, weed killer or use a solution of zinc or magnesium and water.
- Rinse thoroughly with clean, clear water.
- For Industrial Stains: Clean with a water-based household detergent and a stiff bristle brush.