How to Repair Loose Wall Plaster

Chisel out plaster that is broken and crumbling along crack lines. You don't want to cover up broken bits. It is best to clean the bits out, reattach the plaster that has pulled away from the lath, and then fill in a clean, smooth crack line.

Insert screws into the holes of plaster washers. Drill the screws into the wall slowly. If you hit the lath, drill the screw down until the washer is flush with the wall. Do not screw it in too tightly, or you will crack the plaster. Stop when the washer is against the wall. This pulls the loose plaster back to the lath and secures it. If you don't hit the lath, reverse the screw out and repeat until you do. You will patch any holes you create later. Place washers every 4 inches in the loose plaster area.

Fill the cleaned crack lines with a plaster patch. Use a small trowel or putty knife to force the patch material in the crack.

Place strips of fiberglass tape over the cracks.

Dampen the surface with a sponge, then spread a skim coat of plaster patch material over the surface, covering the washers, tape and cracks. The skim coat is a very thin layer of material; you should still be able to see the washers through the coating. You just want to dampen the wall to help the patch material adhere to the old plaster. Let the patch dry overnight, and then sand smooth.

Dampen the wall surface lightly, then smooth on a second coat of patch material so that you can no longer see the washers or tape. Taper this coat several inches beyond the repair area down to the wall surface. Let the wall dry for another day, then sand smooth.

Dampen the wall, then spread on another thin layer of patch material and finish the area to match the rest of the walls. This can be done with the bristles of a brush or the flat edge of a trowel or sponge. If you are unsure of how to apply the finish, practice on a scrap piece of wood before attempting to finish the wall.