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.
- This procedure includes guidance on res-ecuring loose plaster by injecting adhesive behind the loose plaster and securing it with plaster washers.
- Plaster is in need of re-securing when sound plaster has lost its keys and is floating away from the lath or when the plaster and lath are no longer attached to stud or joist.
- If wood lath strips are placed too close together, or the lath is nailed directly over planks, keys do not form properly and the plaster may eventually sag away from the lath. Other factors contributing to sagging plaster include wood shrinkage, weight of plaster or broken vertical ties (see 09210-06-R).
- See "General Project Guidelines" for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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).
- Charles Street Supply Company
- USG Corporation
- TKO Industrial Coatings, LLC
NOTE: When the common name of a chemical is used on the label, it is usually a sign that the substance is not as pure as the same chemical sold under its chemical name. However, the grade of purity of the common-name substance is almost certain to be adequate for stain removal work, and because it is likely to be less expensive, the common-name product should be purchased when available. Common names are indicated by an asterisk (*).
- Denatured Alcohol:
- Other chemical or common names include Methylated spirit*.
- Potential hazards: TOXIC AND FLAMMABLE.
- Available from hardware store, paint store or printer's supply distributor.
- Denatured alcohol should be a satisfactory substitute for ethyl alcohol for stain removing purposes.
- Plaster Washers suppliers: Charles Street Supply Co., hardware and building supply firms, internet search, or approve equal.
- Acrylic, laytex or polymer emulsion adhesive (all water- based) such as "StrongStik" Construction Adhesive (DAP), "Liquid Nails", or approved equal.
- Foam carpet pad
- Wood shingles
- Joint compound such as "Durabond Setting-Type Joint Compound" (USG.com), "Krack-kote" (TKOCoatings.com), or approved equal.
- Flat head wood screws or drywall screws and plaster washers
- Clean, potable water
- Electric drill
- Bent wire tool
- 1/2 inch plywood
- 1 x 2 or 2 x 4 wood braces
- Caulking gun
- Phillips head screwdriver
- Determine the extent of the damage and evaluate work requirements and causes before proceeding.
- Thumping with a finger makes a solid, snappy sound on good plaster; it makes a hollow and dull sound on loose plaster.
- Gently press the plaster surface with palm of hand or with a T-brace made from 2x4s; If plaster moves in relation to the studs and lath, then the keys are broken; With more pressure, a similar movement indicates that the plaster is well keyed to the lath, but the lath is loose from the studs
3.02 ERECTION, INSTALLATION, APPLICATION
- Resecuring Plaster by Injected Adhesive Bonding:
- Determine the areas of loose plaster and mark them out with chalk (see section 3.01 EXAMINATION).
- Ceilings (accessible backside):
- From the backside of the surface to be repaired, drill 1/4 inch injection holes through the lath 3-6 inches apart and at the center of the lath (use a drill stop on the bit to keep from drilling into the plaster).
- Using a bent wire tool and a vacuum, loosen and suck dust out through the injection holes.
- Ceilings (inaccessible backside) and Walls:
- Drill through plaster and lath with holes 3-6 inches apart, and if possible, through the center of the lath.
- In walls, break-the plaster open at the bottom of loose areas and vacuum up debris left by broken keys.
- Have 1/2 inch plywood as big as the patch area and enough 1x2 wood braces on hand.
- Trim the tip of the caulking-gun cartridge so that it fits in the wood-lath holes.
- If selected adhesive has an adhesive primer, squirt into pre-drilled holes according to manufacturer's instructions.
- If adhesive has no primer, mix 4 parts water, 2 parts denatured alcohol and 1 part adhesive (water-based only).
- Pre-wet both the plaster and lath.
- Inject adhesive into the pre-drilled holes, giving the adhesive enough time to flow into the space between the plaster and the lath.
- T-brace a 1/2 inch layer of foam carpet padding between the plywood and the plaster; Add additional braces as necessary or drive screws through washers and wood shingles to draw the plaster up against the lath.
- When the adhesive has set, carefully remove the plywood (it may need to be twisted gently to break the bond).
- Fill holes and/or tape and mud cracks and finish as required.
- Re-securing Loose Plaster with Plaster Washers: Use plaster washers (also called repair discs or ceiling buttons) to pull sound plaster back up to the lath (when the keys have broken), or to pull plaster and lath back to the studs or joists.
- If the lath was nailed directly to the joists or rafters, find the joists, then measure and mark their locations with chalk lines snapped across the ceiling.
- From below, drive 1-1/2 to 2 inch gyp-board screws, fitted with plaster washers, through the plaster and lath up into the joists. Space every 4 inches on each joist where sagging is apparent, or as often as necessary, and 1-1/2 inches from the edge of the loose section (only screws that hit lath will hold).
- Tighten the screws gradually all along the edge.
- Patch the holes with spackling or joint compound and finish with a skim coat of joint (taping) compound.
- Remove all rubbish and debris caused by plastering work.
- Clean all affected surfaces of room and furnishings to their prior condition.