Repairing Plaster Walls

Before gypsum wallboard became the interior surface finish material of choice in the 1 950s, plaster was very commonly used for finishing interior walls and ceilings. Plaster is a very hard and durable material, but-because it isn’t a resilient material-it has a tendency to crack as a home moves with earthquakes or naturally settles over the years. Once cracks form, plaster may eventually work loose.

A mixture of portland cement, sand, and water, plaster may be applied over wood lath, metal mesh, special gypsum wallboard, or masonry. During application, a scratch coat is applied onto the backing material. Next, a thick undercoat is troweled onto the surface, then a finish coat is applied.

Here you’ll find instructions for patching cracks and holes in plaster. If a large area is damaged or the base needs repair, consult a professional.

Small Cracks And Holes Fine cracks, nail holes, and small gouges in plaster usually can be repaired with spackling compound. Widen the hairline cracks to about ‘/s inch with the tip of a lever-type can opener; blowout dust and debris. With your finger or a putty knife, fill the crack with spackling compound. Sand the compound in a circular motion when dry, using a block wrapped with fine-grade sandpaper. Prime the patch with sealer before painting.

Large Cracks For larger cracks, undercut the crack with a lever-type can opener or a putty knife to help bond the new plaster; blowout dust and debris. Dampen the crack with a sponge, then use a putty knife to fill just over half the depth of the crack with patching plaster. Score the plaster with a nail when firm but not hard to provide “bite” for the next layer. Dampen the dry patch again and use a broad knife to apply the next layer to within ‘/s and ‘/, inch of the surface. Let the patch dry before applying the finish coat. Fill with finishing plaster and strike off with a straightedge to remove excess.

Finishing Tips Matching an existing texture requires skillful treatment of the still-wet finishing plaster. You’ll have to experiment to achieve a good match. For a smooth surface, pull a metal float or wide putty knife dipped in water across the plaster. When dry, sand to remove minor imperfections, prime, and paint. For a textured surface, use paintbrush, stippling brush, household sponge, sponge float whisk broom, or wire brush-whatever will give you the desired finish. Daub or swirl the plaster-in a uniform, random, or overlapping pattern. To create peaks in the plaster use a brush or a tool with bristles; when the peaks start t stiffen, gently draw a clean metal float over the surface to smooth them. Let the plaster dry, then prime and paint.

Repairing Plaster

1. Prepare the hole

Remove cracked plaster from the edges of the hole with a cold chisel and hammer. Undercut the edges to ensure a good bond; blow away debris. Dampen the edges with a sponge.

1. Apply a first coat

Using a brood knife, fill a little more than half the hole’s depth with patching plaster; force it through gaps in the lath. Score the plaster with a nail when firm and let it dry.

1. Apply a second coat

Dampen the patch again; use a brood knife to apply a second layer of plaster 10 within 1/8 and ¼ inch of the surface. When firm, score the plaster with a nail to provide “bite” for the next layer; allow 10 dry.

1. Apply the finish coat

Use a broad knife or a 10-inch taping knife to apply finishing plaster; feather the edges an inch or more beyond the edges of the patch. Remove excess wet plaster with a straightedge. For a smooth finish, dip a metal float in water and, holding the float at a slight angle to the wall, draw it down from top to bottom. When dry, sand and prime.

If The Hole Has No Backing

If there isn’t any lath or backing to support a new coat of plaster, your patching material will just fall down into the wall-so you need to provide backing. After preparing the hole, loop a wire through a piece of rust-resistant metal mesh. Roll the edges, insert the mesh into the hole, flatten it out by pulling the wire, then wind it up with a stick. After you’ve patched the hole, remove the stick and snip off the wire.