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 applying Benzotriazole (BTA) to outdoor bronze in order to inhibit corrosion of the metal. This procedure is primarily intended to follow the removal of barrier coatings, such as wax or Incralac, prior to recoating.
NOTE: BTA is regularly applied to bronze as an additive to wash water.
- For general information on the characteristics, uses and problems associated with bronze, see 05010-03-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 (*).
- Benzotriazole (BTA), such as "Cobratec" (GAF Corporation), or approved equal
- Other chemical or common names include Ethyl alcohol; Ethyl hydroxide; Ethylic alcohol; Methyl carbinol; Cologne spirits*; Fermentation alcohol*; Grain alcohol*; proof spirit*; Rectified spirit*; Spirits of wine*.
- Potential Hazards: FLAMMABLE; moderate toxicity if ingested, inhaled, or by skin contact; (see CAMEO Material Database, Museum or of Fine Arts, Boston, for more information).
- Available from chemical supply house, hardware store or liquor store.
- Denatured alcohol, which carries no liquor tax, should be a satisfactory substitute for ethyl alcohol for stain removing purposes.
- Clean, potable water
3.01 ERECTION, INSTALLATION, APPLICATION
- Wash the bronze surface to remove loose dirt and allow to dry.
- Mix a 2 to 1 solution of water:ethanol.
- Add a 3% solution of BTA to the water-ethanol mixture.
- Brush the solution onto the bronze and allow to dry for one hour.
- Brush apply a second coat of the solution and, again, allow to dry for one hour.
- Rinse the surface thoroughly with clean, clear water from top to bottom to remove excess, crystallized BTA.
- Allow the surface to dry for 48 hours before any additional treatments.