How to Fix a Cracked Plaster Wall (Step-by-Step DIY Guide)

Plaster cracks are almost always fixable at home — you just need the right approach and a bit of patience between coats. Here's how we do it on the job, boiled down for DIYers.

First — figure out what kind of crack it is

• Hairline crazing — spider-web fine, usually cosmetic. Easy fix.
• Straight-line crack along a join — the tape's failed. Very common. Fixable.
• Diagonal crack from a corner (window, door) — movement. Fixable but may come back if the house is still moving.
• Wide crack (5mm+), staircase pattern, or one you can see daylight through — structural. Stop, call a builder before you plaster over it.

What you'll need

• Utility knife or 5-in-1 tool
• Fibreglass mesh tape (better than paper for DIY)
• Jointing compound (Gyprock Base Coat or all-purpose)
• 6" and 10" taping knives
• Sanding sponge or 120-grit sandpaper on a block
• Dust sheet, dust mask, primer, paint

Step-by-step

1. 1Rake out the crack. Run your knife along it to open it up slightly and remove loose bits. Sounds counterintuitive, but a wider V-groove holds compound properly. Vacuum the dust out.
2. 2Tape it. Press fibreglass mesh tape centred over the crack. Cut cleanly at each end.
3. 3First coat. Load the 6" knife with compound and press it firmly through the mesh so it fills the crack and bonds to the plaster. Skim smooth over the tape, feathering the edges outward. Let it dry fully (usually overnight).
4. 4Second coat. Use the 10" knife this time. Apply a wider, thinner coat blending 5–10cm past the first coat on each side. Dry overnight.
5. 5Third coat (finish). Very thin skim, even wider than coat two. This is the coat that hides the repair, so take your time. Dry overnight.
6. 6Sand. Light sanding with 120-grit — you want the surface flat and blending seamlessly. Wipe the dust off.
7. 7Prime and paint. Always prime the patch first, or the paint will flash (look glossier over the repair). Then paint the whole wall corner-to-corner if you can — spot-painting almost always shows.

Common mistakes

• Skipping the tape. Compound alone will crack again within months.
• One thick coat instead of three thin ones. Thick compound cracks and sags.
• Not letting it dry between coats. Trapped moisture = future cracks.
• Sanding too aggressively and blowing through into the compound.
• Painting without priming. Every time.

When to call a plasterer

If the crack keeps coming back, it's on a ceiling, it's over a metre long, or the surrounding plaster feels soft or crumbly — get a pro in. Same if it's in a rental or an insurance job where the finish needs to be spot-on. In Hervey Bay and across the Fraser Coast, we do small repair work all day long — no minimum job size.