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How to Repair Cracked Plaster Walls

Home/Resources/Paint & Walls/Repairing Cracked Plaster
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Written & researched by Priya Anand DIY & Tools Editor
Updated August 2026
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Repairing cracked plaster is a rewarding DIY job for older homes, but it has one gate: telling a cosmetic crack from a structural one. Thin, stable cracks are DIY — reattach loose plaster, tape, fill, skim, and paint over a couple of days plus dry time, for under $50 in materials. But wide, growing, or diagonal cracks from door and window corners, especially with sticking doors or sloping floors, can signal foundation or framing movement and deserve a professional look before you patch. For ordinary cracks, the durable-repair secret is to stabilize the loose plaster and tape the crack before filling, so it does not simply reopen.

How to Repair Cracks in Plaster Walls — Ask This Old House

Step-by-step: repairing a cracked plaster wall

  1. Assess the crack. Rule out structural warning signs — wide, diagonal, growing cracks with sticking doors or sloping floors need a pro first. Proceed with thin, stable cosmetic cracks.
  2. Reattach loose plaster. Press the plaster near the crack; if it flexes, secure it back to the lath with plaster washers and screws (or adhesive) so it cannot move.
  3. Prepare the crack. Scrape out loose debris and lightly widen and undercut a fine crack so filler can key in. Vacuum the dust.
  4. Tape the crack. Embed mesh or paper tape over the crack in a bedding coat of joint or setting-type compound, pressing out the excess. The tape bridges the joint so it resists reopening.
  5. Fill and build. Fill the crack and any depressions with compound (setting-type for strength on bigger repairs), building up in thin layers and letting each dry.
  6. Skim and feather. Skim a finish coat over the taped repair, feathering wide into the wall. For a badly crazed wall, skim the whole surface smooth.
  7. Sand, prime, paint. Sand flush under a raking light, prime the bare compound, and paint the wall corner to corner.
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Tools and materials

You need plaster washers and screws, a drill, mesh or paper tape, joint or setting-type compound, taping knives, sandpaper, primer, and paint. The finishing steps overlap with our skim coating and taping and mudding guides. Old plaster walls often show every flaw, so a good finish paint that levels smoothly helps — see our interior paint picks. A quality roller keeps the repaired wall's texture even, and clean painter's tape protects trim while you prime and paint.

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Mistakes that reopen the crack

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When to call a pro

Get a professional assessment for cracks wider than about a quarter inch, cracks radiating diagonally from door and window corners, stair-step cracks, or any crack that keeps growing or pairs with sticking doors and sloping floors — these can indicate foundation or framing movement that patching will not solve. Pre-1978 homes may have lead paint over the plaster; do not dry-sand it, and follow lead-safe practices.

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More from this hub: Paint & Walls · Skim coating a wall · Patching a hole · Repairing peeling paint · Best interior paint · How we rank

Straight Answers

Frequently Asked

Why do plaster walls crack?

Old plaster cracks from house movement, from the plaster losing its grip on the wood lath behind it, and from ordinary settling and seasonal expansion. In older homes, plaster was troweled over thin wood lath strips, and over decades the plaster keys (the bits that ooze through and grip the lath) break, so the plaster loosens and cracks. Vibration, a settling foundation, and humidity swings all add stress. Most of these cracks are cosmetic and fixable. The repair has to address both the crack itself and any loose plaster around it, or it will simply crack again along the same line.

How do you tell a cosmetic plaster crack from a structural one?

Cosmetic cracks are thin, follow no particular pattern or run along lath lines, and do not change much over time. Warning signs of a structural issue are cracks wider than about a quarter inch, cracks that run diagonally from the corners of doors and windows, stair-step cracks, cracks that are actively growing, or ones paired with sticking doors, sloping floors, or a bulging wall. Those suggest foundation or framing movement and warrant a professional assessment before you just patch over them. When a crack keeps reopening after a proper repair, that too points to ongoing movement that needs diagnosing rather than more filler.

How do you keep a plaster crack from coming back after you fill it?

Reattach any loose plaster around the crack first, then bridge the crack with tape before filling. If the plaster on either side of the crack is loose from the lath, screwing it back tight with plaster washers (or injecting adhesive) stops it moving — filling a crack between two loose edges just cracks again. Once the plaster is stable, embed mesh or paper tape over the crack in joint compound so the tape spans the joint and resists reopening, then fill and skim over it. Stabilize, tape, then fill: that sequence is what makes a plaster crack repair permanent.

What do you fill plaster cracks with?

Joint compound works for hairline and small cracks after taping, but for wider cracks or areas where plaster has come away, a setting-type compound or a patching plaster is stronger and better matched to the wall. Setting-type compound (the kind that hardens chemically in a stated time) resists cracking and builds depth without shrinking as much as premixed joint compound. For deep repairs, build it up in layers. Widen a crack slightly and undercut its edges first so the filler locks in. Match the filler to the crack: taped joint compound for fine cracks, setting compound or patching plaster for bigger repairs.

Can you skim coat over cracked plaster to smooth it?

Yes, once the cracks are stabilized and taped, a skim coat over the whole wall is a common way to get old, crazed plaster looking smooth and new. First reattach loose plaster, tape the significant cracks, and fill deep areas, because a skim coat alone will not hold a moving crack together. Then skim the wall in thin coats to bury the taped repairs and the surface crazing, sand smooth, prime, and paint. This is often the best route for a wall with many fine cracks — repair the active ones, then skim the whole surface flat rather than chasing each crack.