Plaster washers are used to hold sagging drywall or plaster walls when cracked or loose from the lath. They are small perforated metal "buttons" and are sunk in the middle as they are specifically designed for drywall screws. The perforations are designed to hold compound or spackle and easily hide repairs.
Screw in plaster washers with drywall screws along the loose plaster ceiling. Make sure to drive the screws into the lath. Screw in as many plaster washers needed along the cracked or loose ridges of the plaster ceiling.
Use a trowel to apply joint compound over the loose edges, covering the plaster washers. Smooth out evenly with trowel. Use several thin coats rather than one thick coat.
Cut a section of screen mesh or insect mesh and lay into the joint compound while still wet. Smooth over with trowel. Apply more joint compound if necessary to cover any mesh.
Let the joint compound dry for 24 hours.
Using 100-grit sandpaper, sand off any high spots to smooth the surface. Apply another thin layer of joint compound if necessary to level low spots.
Once dry, apply primer and paint.