Plastered walls are composed of three layers: a base coat, a thick coat of plaster for strength and a finishing coat for appearance. These may be applied over wood lath, metal mesh, special gypsum wallboard or masonry.
Patching Fine Cracks
- Widen the crack to about 1/8-inch with the tip of a lever-type can opener.
- Blow out the dust and debris.
- With your finger or a putty knife, fill the crack with spackle.
- Sand the spackle when dry, using a block wrapped with fine-grade sandpaper, sanding in a circular motion.
- Prime the patch with sealer before painting.
Patching Wide Cracks
- Undercut the crack with a lever-type can opener or a putty knife to help bond the new plaster.
- Blow out dust and debris.
- Dampen the crack with a wet paintbrush or sponge.
- 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.
- Wet the dry patch again.
- Use a broad knife to apply the next layer to within 1/8 to 1/4 inch of the surface.
- Let the patch dry before applying the finish coat.
- Fill with finishing plaster and scrape with a straight edge to remove excess plaster.
- Experiment with different ways to achieve a good match for existing textures.
- When dry, prime and paint.