Removing efflorescence from plaster

By The Old House Web
PART 1---GENERAL1.01 SUMMARY A. This procedure includes guidance on removing efflorescence from plaster surfaces. 1. Efflorescence is a condition where white (salt) deposits (in the form of a fluffy powder) form on the plaster surface. The formation of salts is usually a sign of excessive amounts of moisture in the back-up material, such as brick or concrete. 2. Salt deposits on the surface may develop from soluble compounds within the adjacent masonry or in the soil. In the presence of water, these compounds gradually migrate to the wall surface, where they remain when the water evaporates. 3. These deposits are generally not harmful to the material, just unattractive. However, they should be removed from the surface as soon as possible. PART 2---PRODUCTS2.01 EQUIPMENT A. Clean sponge B. Stiff, fiber bristle brushPART 3---EXECUTION3.01 EXAMINATION A. Before proceeding with steps to remove efflorescence, examine the plaster and substrate material for potential sources of moisture and make repairs as required: 1. Determine the age of the structure: Efflorescence on older buildings is typically caused by the presence of soluble salts in the construction combined with moisture. 2. Determine the location of the efflorescence: Examination may show where the water is entering. 3. If possible, examine the condition of the back-up material: a. CAREFULLY EXAMINE the wall for open gaps or cracks in joints and around openings that could allow water to enter the building. 1) Are joints properly caulked or sealed? 2) Are flashings and drips in good condition? 3) Are there open or eroded mortar joints in copings or in sills? b. Carefully note the condition and profile of the mortar joints. c. Repair cracks in masonry and/or repoint as necessary before proceeding with the cleaning operations. 4. Examine wall sections and details of construction: Carefully examine roof and wall junctures and flashing details for possible sources of moisture entry. 5. Examine laboratory test reports on the materials: The problem may stem from the composition or misuse of the material.3.02 ERECTION, INSTALLATION, APPLICATION A. Carefully remove any surface deposits using a stiff fiber bristle brush only. B. Wipe the surface with a clean, damp cloth.
Source: U.S. General Services Administration Historic Preservation Technical Procedures

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