Cleaning Masonry Using Ammonium Fluoride Treatment

CSI Division
Division 4- Masonry
Section
Masonry Cleaning
Last Modified

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.

PREFACE: The cleaning or removal of stains from masonry may involve the use of liquids, detergents or solvents which may run off on adjacent material, discolor the masonry or drive the stains deeper into porous masonry. Use the products and techniques described here only for the combinations of dirt/stain and masonry specified.

PART 1–GENERAL

1.01 SUMMARY

  1. This procedure includes guidance on the removal of dirt from masonry by poulticing with an ammonium fluoride paste.
  2. Safety Precautions:
    1. DO NOT save unused portions of stain-removal materials.
    2. DO NOT store any chemicals in unmarked containers.
    3. EXCELLENT VENTILATION MUST BE PROVIDED WHEREVER ANY SOLVENT IS USED. USE RESPIRATORS WITH SOLVENT FILTERS.
    4. No use of organic solvents indoors should be allowed without substantial air movement. Use only spark-proof fans near operations involving flammable liquids.
    5. Provide adequate clothing and protective gear where the chemicals are indicated to be dangerous.
    6. Have available antidote and accident treatment chemicals where noted.
  3. See “General Project Guidelines” for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
    1. Safety Precautions
    2. Historic Structures Precautions
    3. Submittals
    4. Quality Assurance
    5. Delivery, Storage and Handling
    6. Project/Site Conditions
    7. Sequencing and Scheduling
    8. 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).
  4. For additional information on poulticing, see 04455-02-R.

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 (*).

  1. Ammonium fluoride:
    CAUTION: USE EXTREME CAUTION WITH THIS MATERIAL.
    1. Other chemical or common names include Ammonium bifluoride; Ammonium hydrogen fluoride.
    2. Potential Hazards: TOXIC; CAUSTIC TO FLESH; CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS; FLAMMABLE.
    3. Available from chemical supply house or dairy supply distributor.
  2. White absorbent material such as molding plaster, untreated white flour, powdered chalk, talc, fullers earth, etc.
  3. Mineral water

2.02 EQUIPMENT

  1. Glass or ceramic bowl for mixing ingredients
  2. Wooden utensil for stirring the ingredients
  3. Wood or plastic spatula
  4. Brushes - one fine stencil brush, and a natural bristle brush

PART 3–EXECUTION

3.01 PREPARATION

  1. Protection: Provide adequate wash solutions (i.e. water, soap and towels) before starting the job.

3.02 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.

  1. Mix ammonium fluoride with one of the white absorbent materials listed in Section 2.02 above to form a thick paste.
  2. Thoroughly wet the surface to be treated with mineral water.
  3. Apply the paste with a fine stencil brush (be sure to eliminate any air pockets or voids created in the application).
  4. Let the paste dry for twenty minutes.
  5. Carefully remove the paste with a wood or plastic spatula, or a stiff natural bristle brush.
  6. Thoroughly rinse the surface with clean, cool mineral water and allow to dry.
  7. Repeat as necessary to achieve the desired level of cleanliness.

 

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Last updated: Apr 23, 2024
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