To repair damage to plaster walls, first examine the wall to determine the nature of the damage. Common types of damages on plaster walls include hairline cracks and holes on internal and external walls. Start by placing an old towel or dustsheet down to protect the floor. You need a spackling tool, patching plaster, a putty knife, sand paper and a plaster trowel to repair most types of damage.
To repair a hairline crack on a plaster wall, widen the crack a bit. Remove some plaster from the crack to provide a better seat for the fresh plaster. Clean out dust or loose plaster, and then use a spackling tool to fill the crack with plaster. Allow the patch to dry for 24 hours before sanding and painting it if necessary.
To repair holes on a plaster wall, use a soft brush to remove dust and loose plaster around the hole. Carve under the edge of the broken plaster to provide a better seat for the new plaster. Dampen the edge of the hole with a little water, and then use a spackling tool to plaster the patch. Allow the patch to dry for 24 hours.
After the patch has dried, apply a joint compound to the surface of the patch and spread it over the edges of the wall. Ensure the patch is even with the existing wall, and then paint it if necessary.