Patching large holes in plaster with drywall

By The Old House Web

PART 1: GENERAL1.01 SUMMARY This procedure includes guidance on patching holes in wall plaster larger than 4 inches in diameter. When large sections of plaster are missing, drywall patches can be used as a base. PART 2: PRODUCTS2.01 MATERIALS A. Drywall and joint compound B. Nails and screws C. Joint tape (cloth mesh preferred)2.02 EQUIPMENT A. 6 inch taping knife B. 12 inch taping knife C. Float D. Hawk E. Sanding sponge (medium fine grit) F. Stiff putty knife G. Goggles, work gloves, and dust mask H. Hammer and cold chisel I. Needlenose pliers and wire cutter J. Screwgun and drill K. Spray bottle and drop cloths L. Tin snips M. VacuumPART 3: EXECUTION3.01 EXAMINATION A. Determine the extent of damaged plaster. Look for: 1. Holes. 2. Water Stains: Brownish rings on the plaster, especially the ceilings, indicate that the plaster has been wet. If the water was stopped quickly, the surface may only need to be sealed with pigmented shellac to prevent the stain from bleeding through the new paint or wallpaper. However, if the leak continued for a long period, the plaster may need to be replaced, and will often have a powdery appearance. 3. Chipping, flaking and delamination of plaster due to water infiltration. 3.02 ERECTION/INSTALLATION/APPLICATION A. Removing Deteriorated Plaster: 1. Wear a dust mask, goggles and gloves and pull loose plaster from the walls with your hands (a flat prybar may also be helpful in removing plaster that is difficult to remove by hand). 2. To remove sound plaster, for whatever reason, drill holes in the line of your cut with a carbide drill bit; Holding the chisel at a shallow angle, carefully cut directly from hole to hole with a cold chisel; Cut the resulting plaster free from the lath by chipping the keys from the side. 3. Cut the plaster back to the nearest studs to make a regular opening, and re-secure the lath with drywall nails. 4. Use plaster washers and wood screws to re-secure weakly-keyed areas of sound plaster to the wall or ceiling. 5. Knock any plaster stuck between the lath back into the wall cavity. 6. Vacuum all dust, loose plaster, and other debris from the hole with a shop-vac, or sweep it out with an old paintbrush. B. Making a Sheetrock Patch: 1. Shim the Sheetrock as required to bring it up flush with the surface of the adjacent plaster. 2. Cut a Sheetrock patch to fit neatly in the opening. 3. Nail or screw the sheetrock in place; Nailheads or screwheads should be set slightly below the surface of the Sheetrock, but without breaking the paper. 4. Using the 6 inch taping knife, fill the joint between the Sheetrock and the plaster with a small amount of joint compound. 5. Apply a fairly smooth, heavy coat of compound over the joint a little wider than the tape width. 6. Center the joint tape over the length of the joint; Hold the 6 inch taping knife at a 45 degree angle and press the tape into the compound; Smooth out any air pockets under the tape. 7. Apply a thin layer of compound over the tape and apply a first coat of compound to nails or screws. 8. Knock off any ridges or pimples that develop from shrinkage and cracking in the compound. 9. Apply the second coat of compound with the 6 inch taping knife and feather the edges out 6-8 inches; Scrape off any ridges or bumps. 10. When the second coat is dry, apply the third coat of compound with the 12 inch taping knife and feather the edges out 12-14 inches. 11. Touch up low spots with additional compound or high spots by light sanding with a wet sanding sponge.

Source: U.S. General Services Administration Historic Preservation Technical Procedures

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