Patch a hole in a plaster wall

How plaster walls are built

Older homes usually have plaster walls instead of drywall. Wet plaster was spread over wood strips, called lath, with small gaps between them. The plaster squeezed through the gaps and hardened into little hooks, called keys, that hold it to the wall.

When keys break, from settling, a door banging, or water, the plaster comes loose from the lath and bulges, cracks or falls out. That's why a hole in plaster is often bigger than it first looks. A patch over loose plaster cracks again, so the key steps are finding the solid edge and fastening the loose areas back to the lath before filling.

Why plaster comes loose

Let's fix it

1. Test for lead and protect the roomIn a home built before 1978, the paint may contain lead; test it before you scrape or sand, and follow lead-safe practices if it's positive. Lay a drop cloth, cover vents, and wear a dust mask and safety glasses. Plaster dust is fine and spreads.
   Done

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2. Find the solid edgesPress gently around the hole with your palm. Plaster that moves, sounds hollow when tapped, or crunches has lost its grip on the lath. Mark the edge where it turns solid.
   Done

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3. Reattach loose plasterDrill a small pilot hole through the loose plaster into the lath, then drive a drywall screw with a plaster washer until it's just snug and the plaster is pulled flat. Space them every few inches around the hole. Don't overtighten, or the plaster will crack. If the plaster is too far gone, cut it back to the solid edge.
   Done

   Something went wrong?

   • The plaster cracks when you drive the screw Drill a pilot hole first and stop as soon as the washer is snug.

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4. Clean up the holeCut away crumbling plaster with a utility knife or a cold chisel, tapping lightly, and undercut the edges slightly. Vacuum the dust. Mist the old plaster and lath lightly with water so they don't pull moisture out of the new compound too fast.
   Done

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5. Fill the baseFor a small hole, press setting-type joint compound into it, pushing it into the lath so it forms new keys. For a hole bigger than a few inches, screw a piece of drywall to the lath or framing, cut to fit and a bit thinner than the plaster, so it sits just below the surface. Fill around it with setting compound, then let it harden for the time on the bag.
   Done

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6. Bring it up levelAdd another layer of setting compound until the patch is nearly flush with the wall. Setting compound hardens by chemical reaction, so you can recoat as soon as it's firm, without waiting a day. Keep each layer thin enough to work smoothly.
   Done

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7. Tape and finish coatCover the joints around a drywall patch with mesh tape. Apply a thin finish coat of lightweight compound over the patch with a wide knife, feathering it a few inches past the edges so it blends in. Let it dry, then add a second thin coat if needed.
   Done

   Something went wrong?

   • The patch shows through the paint Prime it first, then add another thin, wide finish coat if it's still visible.

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8. Sand, prime and paintSand lightly with a sanding sponge until it's smooth and flush, wipe off the dust, and prime the patch. Paint it, feathering the paint out past the patch. The guide for touching up wall paint has tips on making it blend.
   Done

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Watch it done

How to Patch Holes in Plaster WallsBy This Old House on YouTube. Their method may vary a little from ours.

Watch on YouTube

If you're hanging something

If you need to hang something on plaster, see the guide for hanging things on a plaster wall without cracking it.

If the wall is drywall, not plaster, the guide for patching a hole in drywall is simpler.

Plaster patching questions