Removing Efflorescence From Plaster

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.




  1. 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.
  2. 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).



  1. Clean sponge
  2. Stiff, fiber bristle brush



  1. 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:
      1. 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?
      2. Carefully note the condition and profile of the mortar joints.
      3. 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.


  1. Carefully remove any surface deposits using a stiff fiber bristle brush only.
  2. Wipe the surface with a clean, damp cloth.
  3. For guidance on cleaning and/or repairing damaged plaster, see "Restoring Metal Leaf On Plaster", "Reducing Lead-Based Paint Hazards Using Abatement Techniques on Windows" "Reducing Lead-Based Paint Hazards Using Interim Control Techniques On Windows" and "Replicating Ornamental Plaster Trim".