Follow painting expert Brian Santos' simple how-to steps for repairing plaster. Read more in his new book, "Painting Secrets."
1. Remove loose material with a putty knife or chisel. Dust the area with a dusting brush. Dampen the edges of the plaster with a commercial latex bonding agent; mix and apply it according to the manufacturer's instructions.
2. Mix patching plaster according to the manufacturer's instructions. Apply the plaster with a broad knife. If the hole is less than 1/8 inch deep, one coat should be enough for good coverage. If the hole is deeper, apply a base coat of plaster in the hole to within 1/8 inch of the surface.
Press the plaster into the lath. Let this coat set for 15 minutes, then score the surface with a nail to provide tooth for the next layer. Let the base dry overnight.
3. Apply a second layer of patching plaster, bringing it almost to the surface. Let this layer set for one to two hours to harden.
4. Add water to bring the patching plaster to a creamy consistency for the finish coat. Apply the finish coat as smoothly as possible. Make the patched area flush with the surrounding surface. Let the finish coat set for 30 minutes to an hour.
5. Smooth the patch with a damp sponge, blending it into the surrounding surface. This will reduce the amount of sanding necessary. Let the plaster harden.
6. If necessary, apply a texture coat to replicate existing wall surfaces. Blot the patch with a damp sponge, matching it to the surrounding surface. Let the plaster harden.
7. Lightly sand and seal the area with white-pigmented shellac.