Almost every house gets ceiling cracks at some point. Most are harmless and easy to put right, but a few are an early sign of a leak or of a ceiling that’s coming loose. Here’s how to tell the difference, and what can be done about each.
Common types of ceiling crack
Fine hairline cracks
Thin, spidery cracks are very common, especially in older houses. They’re usually caused by the house settling, seasonal movement as the building warms up and cools down, or new plaster shrinking slightly as it dries. On their own they’re cosmetic and can be filled, or covered with a fresh skim.
Straight cracks in a line or grid
Straight cracks running across the room, often at regular spacings, usually follow the joints between plasterboard sheets. They tend to appear where the joints weren’t taped properly or there’s a little movement in the joists. The fix is to cut them out, tape the joints and re-skim.
Cracks where the ceiling meets the wall
Ceilings and walls move slightly differently, so a crack along the top of the wall is common. It can be filled and decorated, or hidden with coving, which covers the joint and gives the room a neater edge.
Cracks with a stain
A crack with a yellow or brown stain around it usually means water has got in from above: a leaking pipe, bath, shower or roof. Find and fix the leak first, then let the ceiling dry out before it’s repaired.
When a crack is more serious
Have your ceiling looked at soon if you notice:
- the ceiling bulging, dipping or sagging
- cracks that are getting longer or wider, or keep coming back after being filled
- a section that sounds hollow or moves when you press it gently
- bits of plaster or dust falling
- ceiling cracks along with doors that have started sticking or new cracks in the walls
If a ceiling is visibly sagging, keep people and furniture out from under it and don’t try to push it back up. Cracking together with sticking doors or cracked walls can be a sign of structural movement, which needs a builder or structural engineer to look at before any plastering is done.
Why old lath and plaster ceilings sag
Houses built before plasterboard became common, including most Victorian and Edwardian homes, usually have lath and plaster ceilings. Thin strips of wood (the laths) were nailed to the joists, and plaster was pushed on so it squeezed through the gaps and curled over the top, forming “keys” that hold the ceiling up.
Over many decades those keys can break. Water leaks, vibration, people moving about in the loft and plain old age all play a part. Once enough keys have gone, the plaster starts to part company with the laths and the ceiling begins to sag.
A lath and plaster ceiling that’s still firmly attached can often be repaired and skimmed. One that sags, sounds hollow or moves needs more than a skim.
A note on textured ceilings: some older textured ceiling coatings contain asbestos. If you have one, have it tested before anyone sands, scrapes or takes the ceiling down.
How cracked and sagging ceilings are repaired
- Filling and re-skimming. For hairline and joint cracks in a sound ceiling, the cracks are raked out, filled and taped where needed, then the ceiling is skimmed so it’s smooth and even again.
- Overboarding. New plasterboard is screwed through the old ceiling into the joists, then skimmed. It suits a tired ceiling that’s still reasonably solid, and avoids the mess of taking the old one down.
- Taking down and replacing. Where the old ceiling is badly sagging or damaged, it’s taken down and replaced with new plasterboard, then skimmed. It’s messier, but it removes the weight of the old plaster and lets the joists be checked.
Which is right depends on the state of the ceiling, so it’s worth having it looked at in person before deciding.
Ceiling repairs in Poole and Dorset
Four Four Finishes repairs, re-skims and replaces ceilings in homes across Poole, Bournemouth and Dorset, from a single cracked ceiling to a whole house. See our ceiling plastering and repairs page, or get in touch for a free, no-obligation quote.
Frequently asked questions
Are hairline cracks in a ceiling normal?
Yes. Fine cracks are very common and are usually caused by the house settling, seasonal movement or new plaster drying out. On their own they’re cosmetic and can be filled or skimmed over.
When should I worry about a crack in my ceiling?
When the ceiling is sagging or bulging, cracks keep getting bigger, there’s a water stain, a section sounds hollow or moves when pressed, or plaster is falling. Keep clear of a sagging ceiling and have it checked soon.
Can you plaster over a cracked ceiling?
If the ceiling is sound, yes. The cracks are filled and taped where needed, then the whole ceiling is skimmed. If it’s loose or sagging, it has to be secured, boarded over or replaced first.
Is it better to overboard or replace a lath and plaster ceiling?
Overboarding is quicker and less messy, and works well on a ceiling that’s still reasonably solid. A ceiling that’s badly sagging or damaged is usually better taken down and replaced with new plasterboard.
Why does my ceiling crack in straight lines?
Straight cracks usually follow the joints between plasterboard sheets, often because the joints weren’t taped properly. They can be cut out, taped and re-skimmed so they’re less likely to come back.