How to Deal With Plaster Walls

Patching Materials

• To repair plaster walls, a ready-mix base-coat plaster is used, especially when large holes must be filled. High-gauge lime putty, manufactured of 50 percent lime and 50 percent gauging plaster is used to produce a white smooth surface that is suitable for surface repairs. This mixture shrinks less than traditional joint compound, which also has the same workability as ready-mix base plaster.

Filling Cracks

• Hairline cracks are easy to repair as long as the underlying structure is in good condition. Those cracks can be filled with common patching material. Cracks due to seasonal humidity must be widened slightly before filling with spackling material. Persistent cracks might need bridging with a fiberglass mesh tape. Larger cracks that stem from structural movement require repair to the underlying structure. In these instances, loose plaster should be removed before applying new plaster to the area and letting it dry.

Patching Holes

• For wall holes smaller than 4 inches, apply a layer of base plaster scraped below the level of existing good plaster. When this has dried, a second layer can be applied to create a level surface. Sometimes a third level might be needed. One coat patching is not recommended because it may produce a concave surface. Underlying old lath may need to be renailed when larger holes occur. Water misting or a bonding agent can be used to keep the new plaster from twisting.
  Ceiling holes occur because the keys holding the plaster to the ceiling have broken. If surrounding plaster is sound, loose plaster can be reattached to the lath via wood screws and plaster washers. Any remaining crevices may be smoothed by filling them with successive layers of plaster.

Sagging Plaster

• As plaster ages, it dries and loses strength, allowing the structure to pull away from the keys that hold it into place. The lath might also pull away from the framing. Sagging plaster signifies both problems. When the sagging area is large, homeowners might want to enlist the help of an expert because the work to repair this heavy material is often difficult. The entire area around the workplace should be protected with plastic sheeting. Plaster that is still in good condition but had been pulled away from the lath or framing can be reattached with nails.