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. Surfacing compound, available in powder, paste, or aerosol form, fills hairline cracks, holes left by picture hooks, and other small blemishes.
Patching plaster must be mixed with water, but it is stronger than surfacing or joint compound. Use it for broad cracks or big holes.
Time: 1 hour of work, but allow for two overnight periods of drying.
Skills: Intermediate skills, particular for getting a smooth finish.
Tools: Hammer, chisel or old screwdriver, putty knife, taping knife, old toothbrush, sanding block, and a sponge.
Step-by-Step
1. Undercut the crack.
Undercut wide cracks, making them broader at the bottom than the surface to lock in the filler material.
2. Clean with a toothbrush.
Clean the debris and crumbly material out of the crack with an old toothbrush.
3. Dampen the damaged area.
Thoroughly wet the crack before patching to ensure a good bond. To prevent future cracking, apply fiberglass mesh tape over the crack.
4. Pack with compound.
Pack joint compound, surfacing compound, or patching plaster into the crack with a putty knife or a wide-blade taping knife. Level off.
5. Apply a second coat.
Let dry 24 hours, then level off the repair with a second application.
6. Seal and paint.
After the second coat has dried, sand smooth, then seal with primer before painting.
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