How to Fix Small Cracks in Plaster

By Gary Hedstrom, Peg Hedstrom, Judy Ondrla Tremore

Repairing small cracks in plaster is easy compared to plastering a whole room. To repair small cracks in plaster, you’ll need patching compound, medium- and fine-grit sandpaper, a sanding block, a putty knife, a masonry chisel, a paintbrush, a rag, and a screwdriver. For finishing, you’ll need primer and paint.

Remember: Plaster repair is much more difficult than fixing drywall. Unless the repair is small, don’t attempt any plasterwork unless you’re trained or experienced. It’s easier to replace a wall or ceiling panel with drywall.

Hit the chisel with a hammer to widen the crack in the plaster.

1Use the chisel to widen and undercut the crack.

By making the back of the crack wider than the front surface (undercutting), you create an opening that the plaster can grip.

2Scrape out all loose plaster with the tip of the putty knife, and wipe away the dust with the rag.

You don’t want any loose particles ending up in the plaster patch.

3Thoroughly dampen the full length of the crack with a wet paintbrush.

Dampen inside the crack, as well. The damp surface will help the plaster adhere well.

Use a putty knife to apply the plaster over the crack.

4With the putty knife, apply a thin coat of plaster patching compound over the crack.

Be sure to feather the edges. Plaster patching compounds can vary, so follow the manufacturer’s directions for use.

Use a sanding block to smooth the patch.

5Let the patch dry completely (usually overnight), and smooth the patch with sandpaper wrapped around a sanding block.

Begin with medium-grit (80-grit) sandpaper to smooth out the bigger bumps. Then, switch to a fine (120-grit) sandpaper to get a fine, smooth finish.

6Paint the patch with primer.

Don’t skip this step or you’ll end up with a permanently goofy-looking, non-matching area.

7Apply touch up paint to the patch in your wall color.

This is why you saved that half a gallon of leftover wall paint.