Step

Widen the crack to about 1/8-inch with a chisel and blow out any loose plaster.

Wipe crack with a dab of surfacing compound, pressing it into fissure.

Seal patches with primer before painting, or the patch may "bleed" through.

If your home has plaster walls, you can resign yourself to patching before every paint job. Harmless cracks will return with regularity no matter how often you fill them. Watch, though, for loose or crumbly cracks, holes, and bulges; these may mean you have a leak. If you have a leak, fix it before doing any work on the walls.

Too much or too little water in the original mix also weakens plaster. It's easier to use premixed materials for small repairs. Drywall joint compound works easily into all but the finest cracks, smooths bumpy surfaces, and fills fairly deep holes in a couple of applications.

Step

Let dry 24 hours, then level off the repair with a second application. After the second coat has dried, sand smooth, then seal with primer before painting.

Spackling hairline cracks: 20 to 30 minutes

Patching large cracks: 1 hour

Step

Undercut wide cracks, making them broader at the bottom than the surface to lock in the filler material.
Clean the debris and crumbly material out of the crack with an old toothbrush.

If you are using plaster for the repair, thoroughly wet the crack before patching to insure a good bond.

Pack the plaster into the crack with a putty knife or a wide blade taping knife.