Gather patching plaster or joint compound, putty knife, sandpaper, utility knife, damp sponge, primer, and paint
Remove loose plaster, dust, and debris from the damaged area
Cut away any crumbling edges to create a stable patch area
Lightly dampen the area if needed
Apply a bonding agent or plaster repair adhesive if required
Fill deep holes or cracks with patching plaster in thin layers
Press plaster firmly into the damaged area
Let each layer dry before applying the next
Use mesh tape for larger cracks or openings
Apply a final thin skim coat over the patch
Feather the edges smoothly with a putty knife
Let the patch dry completely
Sand the patched area until smooth and level
Wipe away sanding dust
Prime the patched area
Paint to match the surrounding wall