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WALLS & CEILINGS

Repair a Crack in Plaster

A lasting plaster-crack repair depends on whether the crack is cosmetic or caused by continuing movement, moisture or loose plaster.

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Check for hidden cables, pipes, loose plaster and moisture before drilling, cutting or removing material

Wear eye and dust protection. Stop if the surface is sagging, heavily damp, contains suspect asbestos materials or shows significant structural movement.

MOST LIKELY CAUSES

Start with these

Normal drying or shrinkage Fine cracks often appear as plaster dries.
Building movement Recurring or widening cracks may indicate movement.
Loose plaster Poor adhesion beneath the surface can cause cracking.
Moisture damage Leaks or damp can weaken plaster.
◫ Symptom variations Match the exact damage, movement or finish defect. ⌄
  • Hairline crack
  • Crack reappears after filling
  • Diagonal crack
  • Crack around door or window
  • Hollow plaster beside crack
✓ Quick checks Simple checks before cutting or filling. ⌄
  1. Identify the wall or ceiling material.
  2. Check for damp, leaks or movement.
  3. Look for hidden service zones.
  4. Remove only loose material.
  5. Choose filler and fixings for the substrate.
1 Step 1 — Assess the crack Check for hidden cables, pipes, loose materials and moisture before cutting or drilling. ⌄

Check width, direction, movement and signs of moisture.

2 Step 2 — Open and clean the crack Check for hidden cables, pipes, loose materials and moisture before cutting or drilling. ⌄

Create a shallow V-groove and remove dust.

3 Step 3 — Fill, reinforce and finish Check for hidden cables, pipes, loose materials and moisture before cutting or drilling. ⌄

Use suitable filler or tape where movement is likely, then sand and repaint.

⌁ Common causes explained Why wall and ceiling defects develop. ⌄

A lasting plaster-crack repair depends on whether the crack is cosmetic or caused by continuing movement, moisture or loose plaster.

⌘ Advanced diagnostics Further checks for recurring or serious defects. ⌄
  • Monitor crack width over time.
  • Inspect adjoining masonry or framing.
  • Check for water ingress.
  • Use scrim or mesh on recurring cracks.
  • Seek structural advice for significant movement.
▣ Parts and materials needed Common materials linked to this repair. ⌄
  • Flexible filler
  • Setting filler
  • Scrim tape
  • Primer
  • Matching paint
! When to call a professional Conditions that should end basic DIY work. ⌄
  • Cracks are widening or structural.
  • The ceiling is sagging or unstable.
  • There is significant damp or water damage.
  • Large areas of plaster are loose.
  • Hidden services or suspect asbestos may be present.
? Frequently asked questions Common wall and ceiling repair questions. ⌄

Can I fill over a moving crack?

No. The cause of movement should be understood first or the repair is likely to fail.

Do I need primer over filler?

Usually yes. Porous filler can flash through paint unless it is sealed or primed.