Wall cracks before repainting: which are cosmetic and which aren't
Before you repaint, the cracks have to be sorted — or they'll telegraph straight back through the new coat. Most are harmless hairlines you can fill; a few aren't. Here's how to tell which is which and patch them properly.
SparkFlow team5 min readPainting over cracks without fixing them is the fastest way to a finish that looks tired within months — the crack just reappears through the fresh coat. Before any full HDB repaint, the cracks get sorted. Most are cosmetic; here's how to tell, and how to patch them right.
Cosmetic cracks (the common kind)
- Fine hairline cracks in the paint or skim coat, often from the wall drying or normal settlement.
- Crazing — a web of tiny cracks, usually old paint layers.
- Cracks along a plaster patch or where two materials meet.
These are surface-level and fill easily — they don't mean anything's wrong with the wall.
| Sign | Cosmetic (fill and paint) | Worth a closer look |
|---|---|---|
| Width | Fine hairline | More than a couple of millimetres / fits a coin edge |
| Pattern | Crazing or along a plaster patch | Diagonal from window/door corners, or stair-step |
| Behaviour | Stays put after filling | Keeps coming back or is growing |
| Surroundings | Clean, dry wall | Damp, staining or bulging plaster |
Cracks worth a closer look
- Wide cracks (more than a couple of millimetres) or ones you can fit a coin edge into.
- Diagonal cracks from window or door corners, or stair-step cracks.
- Cracks that keep coming back after filling, or that are growing.
- Cracks with damp, staining or bulging plaster — that's a moisture issue to fix first, sometimes traced back to a hidden pipe leak.
These don't automatically mean trouble, but they're worth having checked rather than just skimmed over — especially if they're moving. Damp-related cracks in particular won't stay hidden until the underlying leak is fixed first.
How a cosmetic crack is filled properly
- Rake out the crack slightly so filler has something to grip.
- Fill with a flexible filler (rigid filler on a moving hairline just cracks again).
- For wider or recurring cracks, use jointing tape or mesh over the filler so it can't telegraph back — the stage our wall crack repair service doesn't skip.
- Sand flush, then prime the patch before painting so it doesn't flash through the topcoat — the same prep that decides whether a single-room repaint holds up.
The takeaway
Hairline cracks are normal and fill in minutes; wide, diagonal, damp or recurring cracks deserve a look before you paint over them. Either way, proper filling and priming is what makes a repaint last — see our paint finish guide and painting cost guide, or let our painting team handle the prep and finish.
Frequently asked questions
- Do I need to fix wall cracks before repainting my HDB flat?
- Yes. Painting over an unrepaired crack rarely lasts — the crack telegraphs straight back through the fresh coat within months. Cosmetic hairline cracks fill in minutes; the key is filling, taping wider ones, and priming the patch so it doesn't flash through your new topcoat.
- How do I tell if a wall crack is structural or just cosmetic?
- Fine hairline cracks, crazing, and cracks along plaster patches are cosmetic and fill easily. Be cautious of wide cracks you can fit a coin edge into, diagonal cracks from window or door corners, stair-step cracks, ones that keep returning, or cracks with damp or bulging plaster. Those deserve a proper check.
- What filler should I use for cracks before painting?
- Use a flexible filler — rigid filler on a moving hairline just cracks again. Rake the crack out slightly first so the filler grips. For wider or recurring cracks, lay jointing tape or mesh over the filler so it can't telegraph back, then sand flush and prime before painting.
- Why do cracks keep coming back after I fill and paint over them?
- Usually the filler was too rigid, the crack is still moving, or there's an underlying moisture issue. Recurring cracks need flexible filler with jointing tape or mesh over the top. If a crack keeps growing or comes with damp, staining or bulging plaster, have the wall checked before painting again.