Concealing Water Stains On Plaster Surfaces

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 concealing water stains on plaster walls or ceilings using a shellac-based primer sealer. A product, such as white-pigmented shellac can be used to seal, prime and block out existing stains, prohibiting them from bleeding through finish layers of paint.
  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. Zinsser Brand
    Rustoleum Inc.
    Evanston, IL
  2. Kilz Brand
    Masterchem Industries
    Santa Ana, CA


  1. White-pigmented shellac such as "Kilz" (Kilz/Masterchem), "Zinsser" (Zinsser/Rustoleum),or approved equal. Both are available from hardware stores in spray cans or brushable liquid.


  1. Clean sponge
  2. Stiff, fiber bristle brush
  3. Paint brush, roller or airless sprayer



  1. Before proceeding with steps to conceal water stains, examine the plaster and substrate material for potential sources of moisture and make repairs as required. For guidance on cleaning and/or repairing damaged plaster, see 09200-01-S, 09210-02-R, 09210-03-R and 09210-05-R.
    1. Look for signs of water infiltration: Examination may show where the water is entering.
    2. 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.
    3. Examine wall sections and details of construction: Carefully examine roof and wall junctures and flashing details for possible sources of moisture entry.


  1. After source of moisture has been eliminated, allow the surface to thoroughly dry out.
  2. Carefully remove any surface deposits and loose paint using a stiff fiber bristle brush only. Fill cracks and holes as required.
  3. Wipe the surface with a clean, damp cloth.
  4. Apply white-pigmented shellac over the stained area using a brush, roller or airless sprayer. Follow manufacturer's instructions.
    1. Depending on the severity of the stain, multiple coats may be required. If so, allow the first coat to thoroughly dry (typically 45 minutes) before proceeding with additional coats.
    2. If using a brush or roller, apply additional coats in the same direction as the first coat.
    3. If the surface is to be repainted with a high-hiding paint, spot-priming only the stained areas is acceptable. However, if a high-hiding paint is NOT used to finish the surface, spot-priming is NOT RECOMMENDED, as primed areas may appear shiny through the paint finish. (Note: Many ceiling paints have little hiding strength). In such cases, the entire wall or ceiling surface should be primed with the white-pigmented shellac before repainting to produce a more uniform final appearance.
  5. Prime and repaint the entire surface with oil or latex paint as required. For guidance on painting, see "General Guidelines for Painting Exterior and Interior Surfaces" and "Surface Preparation Guidelines For Brick, Metal, Wood And Plaster".