Apply the percolated plaster coat next using the plaster trowel. Apply the "scratch coat" which is a mix of plaster and spackle or joint compound, about 2 parts plaster to 1 part substance. Information on repairing plaster walls, here are a couple of actions that can assist anyone that needs aid in fixing plaster walls. Undercutting all holes in plaster and all cracks wider than 1/8 inch or so need to be damaged a treatment in which some of the old-but undamaged plaster is removed along the inner side of the hole (or fracture) so that the patching product that is utilized as filler will bond safely to the strong plaster around the opening. Beginning at the undercut surfaces at the edges of the hole, use the patching plaster is about a 1/4 inch listed below the surface area of the undamaged plaster around the hole.

Brooklyn Plaster Restoration