Holes come in two basic varieties — ugly and really, really ugly. Okay, beyond that they may also have support behind them (such as lath or drywall) or they may be a gaping hole (like where you removed an electrical outlet or a switch). Both have to be filled slightly differently.
Fixing a Supported Hole
If the hole in question has lath or drywall behind it, here's how to fix it. 1. Using a masonry chisel and a hammer, undercut the edges of the hole to create a lip on the underside of the plaster. This will help the new plaster to hold. Blow or brush away dust and debris, then lightly sponge-dampen the plaster edges.
Tip: Some plaster crumbles easily. If your plaster is prone to crumbling, or if you have trouble getting the hang of undercutting, skip it. Your wall will accept the new plaster without it, as long as the edges are clean of debris.
2. Use a wide putty knife to fill the hole half-full with patching plaster. If you have a wood lath base, force the plaster into the slats. Once the plaster crater is thumbprint firm (but not hard), score it with a nail tip so the next layer of plaster will have something to cling to. Let dry completely.
3. Lightly dampen the set plaster and use your putty knife to spread on another layer of patching plaster, leaving a 1/8 to ¼ inch deep crater. Once the plaster is thumbprint firm, score it again with a nail head. Let dry completely.
4. With your wide putty knife, apply a layer of finishing plaster, smoothing it beyond the hole by an inch or more on all sides. Carefully draw your knife across the patch to the outside to create a smooth transition.
5. Level the plaster using a straight edge (a wide metal or plastic ruler or a wide squeegee works fine). Wipe off excess plaster.
6. Using a straight edge or metal "float" dipped in water, carefully drag the tool at an angle across the patched area. Once the patch looks smooth, allow to dry completely before sanding, priming and painting.
Tip: If you have textured walls, see our section on Making the Patch Match.
Patching a Gaping Hole
To patch a hole that has no support behind it, such as when you're patching over a removed light socket or switch, follow these simple steps:
1. If your plaster is very hard, use a masonry chisel and a hammer to undercut the edges of the hole to create a lip on the underside of the plaster. If it is soft, simply blow or brush away any dust and debris. Cut a piece of fine-holed (1/4 inch) rust-proof wire screen so that it extends beyond the hole by at least one inch all the way around. Loop a piece of flexible wire, (or a long pipe cleaner) across the center of the screen to create a handle, then roll the screen slightly so you can insert it into the hole. Use the wire to pull the screen flat against the opening.
2. Wind the wire end tightly around a chopstick, pencil or anything you have handy. Sponge-dampen the hole's plaster edges and use a putty knife to shove the patching plaster through the screen until the hole is filled halfway. Note: for deep holes, your plaster should be about the consistency of peanut butter.
3. Release the stick and, once the plaster is firm, cut the wire. Before the plaster dries completely, score it with a nail to allow the next layer of plaster to cling. Allow it to dry completely.
4. Dampen the patch and apply a second layer of plaster until the hole is only 1/8 to ¼ inch deep. Score with a nail tip and allow to dry.
5. With a wide putty knife, apply a layer of finishing plaster, smoothing it beyond the hole by at least two inches on all sides. Carefully draw your knife across the patch to the outside to create a smooth transition.
6. Level the plaster using a straight edge (a wide metal or plastic ruler or a wide squeegee works fine). Wipe off excess plaster.
7. Using a straight edge or dipped in water, carefully drag the tool at an angle across the patched area. Once the patch looks smooth, allow it to dry completely before sanding, priming and painting.
8. If you have textured walls, see our section on Making the Patch Match.
Patching Holes 5 Inches or Smaller
If the wire solution seems too complicated for you or if you have trouble making the maneuver, there is another option for holes 5 inches wide or smaller that some find easier to administer. You must have a visible wall support somewhere behind the hole for this to be suitable. The process replaces steps 1-4 above.
1. Brush away any debris from the hole's edges and use a trowel or long putty knife to apply a thick layer of quick-setting compound (such as Durabond) or quick-set patching plaster to the wall support behind the hole.
2. Crumple up a piece of stiff, heavy paper (such as brown postal wrap, a paper grocery bag or butcher paper) and stuff it into the hole until it is densely packed. Make sure the paper has contact with the compound you spread so it will adhere.
3. Apply quick-setting compound or plaster to the area, using the paper as support, until you have a patch that sits 1/8 to ¼ below the wall surface.
4. Once firm, score the patch surface with a nail in preparation for the next layer. Allow the compound to dry. Proceed to steps 5-8 above.
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