Spotting a crack in a wall can be worrying, but most cracks in plaster are nothing to panic about. Plenty are just the house settling or the plaster drying, and they can be filled or skimmed over and forgotten about. A few are worth getting looked at. Here’s how to tell the difference, why plaster cracks in the first place, and how cracked plaster walls are repaired.
Hairline cracks
Fine cracks no wider than a hair are the most common type. They often appear in the corners of rooms, where walls meet ceilings and above doors and windows. Houses move a little through the year as the weather, heating and humidity change, and plaster is rigid, so small cracks are its way of taking up that movement.
Hairline cracks are almost always cosmetic. If one stays the same size, it can simply be filled and painted.
Cracks in new plaster
Fine cracks in a freshly plastered wall or ceiling are common too. Plaster shrinks slightly as it dries, and anything that dries it too quickly, like a heater pointed at the wall or a hot room with the windows shut, makes cracking more likely. New extensions and new builds also settle in their first year or two, which can show as fine cracks in the plaster.
Let new plaster dry slowly and evenly, and don’t fill small cracks until it’s completely dry. Our guide on how long plaster takes to dry explains how to tell when it’s ready.
Cracks around doors and windows
The corners of door and window openings are natural weak points, so short cracks running out from them are very common. Doors being slammed and lintels moving slightly as they warm and cool both play a part. Small, stable cracks here are usually cosmetic. Long diagonal cracks that keep growing are a different matter (see below).
Straight cracks along plasterboard joints
A long straight crack, often across a ceiling or down a stud wall, usually follows a joint between two plasterboards. It can happen when the joints weren’t taped properly or when the boards move a little, for example under a floor that people walk on. It’s a common fault in ceilings. Raking it out, taping the joint and re-skimming usually sorts it out for good. If a ceiling crack comes with sagging or bowing, read our guide to cracked or sagging ceilings.
When a crack needs checking
Most cracks in plaster walls are harmless, but get a surveyor or structural engineer to look at a crack before having it repaired if:
- It’s wider than a few millimetres.
- It’s getting longer or wider over time. Pencil a mark at each end and note the date so you can check.
- It runs diagonally from the corner of a door or window, or is wider at one end than the other.
- The same crack shows on the outside wall too.
- Doors or windows nearby have started to stick or no longer close properly.
Cracks like these can mean the building itself is moving, and that needs sorting before the plaster is repaired. Otherwise the new plaster will just crack again.
How cracked plaster walls are repaired
The right repair depends on the crack and the plaster around it:
- Fine, stable cracks. Raked out, filled with a flexible filler, sanded and painted.
- Cracks that keep coming back. Cut out, reinforced with scrim tape and made good, so the repair moves with the wall instead of cracking again.
- Lots of cracks across a wall or ceiling. If the plaster underneath is sound, a fresh skim coat over taped cracks gives a smooth new finish.
- Cracked plaster that’s also loose or hollow. Tap the wall: a hollow sound means the plaster has come away from the wall behind it. The loose plaster needs to come off and be patched, or the wall re-plastered.
We carry out all of these in homes across Poole, Bournemouth and the rest of Dorset. See our plaster repairs page for more on what we do, or send us a photo of the crack and we’ll tell you what we think it needs.
Frequently asked questions
Are cracks in plaster walls normal?
Fine hairline cracks are very common, especially in newer houses, new extensions and freshly plastered rooms. They’re usually caused by the house settling, timber and plasterboard moving slightly with changes in temperature, or plaster shrinking as it dries, and they’re cosmetic rather than structural.
Why is my new plaster cracking?
New plaster shrinks a little as it dries, and drying it too fast with heaters or in a hot, closed room makes that worse. Fine cracks can also appear along plasterboard joints and around doors and windows as a new building settles. Once the plaster has fully dried, small cracks like these can be filled and painted over.
When should I worry about a crack in my wall?
Get it checked if a crack is wider than a few millimetres, keeps getting longer or wider, runs diagonally from the corner of a door or window, also shows on the outside wall, or appears with doors and windows starting to stick. Those can be signs of movement in the building, so ask a surveyor or structural engineer to look before anyone repairs the plaster.
Can I just fill a crack and paint over it?
For a fine, stable crack, yes. Rake it out slightly, fill it with a flexible filler, sand it smooth and paint. If the same crack keeps coming back, the plaster around it sounds hollow when you tap it, or it’s part of a wider area of cracking, it’s usually better to have the plaster repaired properly.
Will a skim coat hide cracks?
A skim gives a wall a fresh, smooth finish and covers small cracks, as long as the plaster underneath is sound and the crack isn’t still moving. Cracks are usually taped or reinforced first. If the old plaster is loose or the wall is still moving, a skim on its own won’t last.