Patching Small Chips And Cracks In 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 patching small chips, cracks or depressions in plaster surfaces.
  2. See 01100-07-S 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).
  3. For guidance on repairing hairline cracks, see 09210-02- R; for guidance on repairing large holes, see 09200-12-R and 09210-03-R.


  1. American National Standards Institute (ANSI)
  2. American Society for Testing and Materials (ASTM)



A. USG Corporation


  1. Gypsum Plaster Materials:
    1. General: gypsum plastering materials shall conform to ANSI A42.1. Provide neat or ready-mixed materials at installer's option unless indicated otherwise.
    2. Base coat plaster: Perlite gypsum plaster such as "Structo-Lite" (USG Corp.), or approved equal.
    3. Base coat aggregate: Sand.
    4. Finish coat plaster: Keene's cement.
    5. Finishing lime: Type is installer's option.
  2. Bonding Materials: Bonding agent shall conform to ASTM C631.


  1. Joint knife
  2. Sponge or heavy-nap cloth
  3. Crack widener or triangular can opener
  4. Stiff bristle brushes
  5. Hawk
  6. Slicker (flexible straight-edge)
  7. Plasterer's trowel
  8. Margin trowel
  9. Mortarboard and mudpan
  10. Pointing trowel



  1. Scrape loose or damaged finish plaster and peeling paint from surface with chisel or joint knife. Remove material where required to enlarge cracks, chips, holes, etc. to at least 1/2 inch across and undercut to improve bonding of new material.
  2. Brush or vacuum surface to remove dust and debris.
  3. Moisten the surface by lightly spraying a fine mist of clean water from a spray bottle.
  4. Apply skim finish coat over low areas to bring entire< finished surface out flush with the projecting firm and sound layers of adjacent plaster or paint. Form plaster as required to match original configuration and design or ornamental plaster.
  5. Once dry, sand by hand to produce a surface without bumps, cracks or depressions, ready to receive finish treatment.


  1. Upon completion of this work, all floors, walls and other adjacent surfaces that are stained, marred, or otherwise damaged by work in this procedure shall be cleaned and repaired and all work and the adjacent areas shall be left in a clean and perfect condition.
  2. All completed work shall be adequately protected from damage by subsequent building operations and effects of weather. Protection shall be by methods recommended by the manufacturer of installed materials and as approved by the RHPO.