Plaster washers are used to secure loose plaster in walls or ceilings to the lath and framing. They are thin, perforated plastic discs that are designed to be used with small screws to strengthen loose plaster that is in otherwise good condition.
Plaster washers are designed to flatten out on the plaster surface as the screw is tightened, and they can be made unnoticeable by spreading out the patchwork a few inches farther all around than when filling in joints in between drywall sheets. In more visible areas, it may be necessary to countersink the plaster washers with a 1 1/8-inch spade bit. If such countersinking is required, it is important not to do it too deeply. Boring deeper than the plaster finish defeats the purpose because the plaster would not be strong enough to withstand the pressure of the screwed-in plaster washer.
Plaster washers are very useful when repairing large cracks on plaster surfaces. In such cases, it is important to feel around for loose or soft sections of plaster in the vicinity of the crack and secure them and the lath to the framing with a plaster washer. This prevents further cracking around the area and keeps the plaster secure once the crack is filled.