Why does the same crack keep coming back after I fill it?
A crack that returns is being reopened by movement. Filler cannot resist movement, so the answer is either a flexible material, a reinforced repair, or finding out why the wall is moving.
- Difficulty
- intermediate
- Time
- 45 min
- Read
- 3 min
- Safety
- caution
Short answer
Rigid filler in a moving joint always cracks again. Work out what kind of crack it is: seasonal movement at a junction between materials wants flexible sealant, a settled crack in plaster wants raking out and reinforcing with tape or scrim, and a crack that keeps widening wants a professional opinion rather than a repair.
Almost every house cracks. Most of it is harmless: different materials expanding and contracting at different rates, plaster shrinking, a new build settling, timber moving with the seasons. The reason a crack keeps coming back is that filling it treats the symptom. Choosing the right response depends entirely on which kind you have.
Safety
Step by step
- Note where the crack is, not just how big.Cracks at a junction between two different materials — plasterboard to plaster, ceiling to wall, timber to masonry, around a stud partition — are movement joints in disguise. Those materials move at different rates and always will.
- Watch whether it changes with the seasons.A crack that opens in winter and closes in summer, or the reverse, is thermal and moisture movement. It is not going to stop. Rigid filler in it will crack every year.
- Use a flexible sealant where movement is expected.At wall-to-ceiling junctions, around architrave and skirting, and where a partition meets a wall, decorator's caulk or a flexible acrylic is the correct material, not filler. It stretches instead of cracking.
- Rake out and reinforce a crack in the plaster itself.Open the crack out slightly, undercut it, then bed scrim or joint tape over it and skim across. The reinforcement spreads the movement across a width instead of concentrating it in one line.
- Look at the pattern if the crack is in masonry.Cracks that follow the mortar in a staircase pattern, that are wider at the top or the bottom, or that continue through a lintel are telling you something about the structure. GuideHQ has a guide on reading a crack in brickwork.
- Monitor before repairing anything you are unsure about.Mark both ends with a pencil and the date, and photograph it. A crack that has not moved in six months is settled; one that has is worth a professional opinion. Filling it removes your only evidence.
- Accept that some cracks are cosmetic and recurring.A hairline at a ceiling junction in an older house may simply need caulking every few years. That is a maintenance item, not a failure.
If it doesn't work
A fine line reappears exactly along the wall–ceiling junction.
Cause: Two elements moving independently. Very common in houses with timber floors above. — Fix: Caulk rather than fill, and paint over. Expect to redo it occasionally.
A crack reappears down the line of a plasterboard joint.
Cause: The joint was not taped, or the tape has failed. — Fix: Rake out, re-tape with scrim or paper tape, and skim over.
The crack is getting steadily wider month by month.
Cause: Ongoing movement rather than settled movement. — Fix: Stop filling it and get it assessed. This is the one case where a repair is the wrong response.
Questions people ask
Is caulk the answer to every recurring crack?
Only at junctions where movement is expected and the crack is narrow. Caulk in the middle of a plastered wall looks wrong, cannot be sanded flat and will still show.
How wide is worrying?
Width alone is a poor guide. Direction, whether it steps through mortar joints, whether it tapers and whether it is still moving matter more. If in doubt, monitor it and get advice rather than guessing.