Hairline cracks plaster ceiling
Updated: October 2026
You are looking at a line on a plaster ceiling, or at a crack that came back after you filled it last year. A rigid filler can sit in a crack that is already still, shallow, and dry. It cannot hold a joint that is still moving, a leak, or a sag. The decision on this page is fill, decorator's caulk, scrim, or a plasterer. It is not the method for a round hole, which is the [how to fill holes](/hub/paints-and-varnishes/plaster-indoor/sub/plaster-indoor-how-to-fill) page. The Products Compared editorial team used public UK guides and the amazon.co.uk notes in our [indoor plaster comparison](/hub/paints-and-varnishes/plaster-indoor) on 21 October 2026. We did not test movement. A qualifying purchase can earn a commission at no extra cost to you.
You are looking at a line on a plaster ceiling, or at a crack that came back after you filled it last year. A rigid filler can sit in a crack that is already still, shallow, and dry.
You are looking at a line on a plaster ceiling, or at a crack that came back after you filled it last year. A rigid filler can sit in a crack that is already still, shallow, and dry. It cannot hold a joint that is still moving, a leak, or a sag. The decision on this page is fill, decorator's caulk, scrim, or a plasterer. It is not the method for a round hole, which is the how to fill holes page. The Products Compared editorial team used public UK guides and the amazon.co.uk notes in our indoor plaster comparison on 21 October 2026. We did not test movement. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Listed job | Form | Depth claim | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Soudal Soudal Repair Express Plaster 290 ml | Cracks, holes, joints | Ready mixed | n/a | 9.6 | about £9.12 | View offer |
 Palace Palace fine surface filler 600 g | Fine cracks and nicks | Ready mixed | Layers max 3 mm | 9.2 | about £1.25 | View offer | |
| Best value |  Palace Palace interior patching plaster 1.5 kg | Walls and ceilings | Powder | n/a | 9.0 | about £2.49 | View offer |
On this page
What kind of crack you have
Sort the line before you open a tub. A hairline is a thin crack in the face of the plaster, often random, with no brown stain and no drop in the ceiling. A straight crack that follows a board joint runs in a line you could mark with a ruler, often where two sheets of plasterboard meet. A corner crack sits where the ceiling meets the wall, or where the wall meets a skirting. A stained crack, or a crack in a ceiling that sags, is a fourth kind. The stain means water has been through. The sag means the background is failing. Checkatrade's ceiling-crack guide separates hairline, straight joint cracks, and stained or sagging cracks for that reason.
A crack that reopened through paint is movement until you can show it is not. Tap the plaster beside the line. Solid and dry can go to a fine filler if the crack is still a hairline. Hollow, soft, or damp does not.
A crack that is still
A still hairline needs a key, not a smear. Which? in its paint-a-room guide, says to open a hairline slightly so the filler has something to grip. You are making a shallow V, not a trench. Dust it out. Then press in a fine filler and leave it slightly proud. Palace fine surface filler is the ready-mixed product UK reviewers use on fine cracks, and the bullets keep deeper repairs to layers of no more than 3 mm. If the line is stable and shallow, that listing is the one with the large review sample on the best patching plaster page. Sand when the pack is dry. On a ceiling, dust falls into your face, so sand lightly, ventilate, and wipe before emulsion.
Which? uses caulk at corners and next to wood, not as the filler for a crack in the middle of a ceiling. Checkatrade uses mesh once a ceiling line is more than a hairline. A stable hairline in the field of the ceiling gets filler. Do this before the mist coat.
Corners and joints that move
Where the ceiling meets the wall, the two surfaces move by different amounts. A rigid filler bridges that joint and then cracks along the same line. Which? says to use decorator's caulk there, and next to wood such as a skirting, and not silicone, because silicone usually will not take emulsion. Bostik's UK note on decorator's caulk makes the same split: junctions, where a rigid repair will crack, and not a place with constant water. Caulk is a flexible bead in the corner, tooled off, then painted once it is ready.
A straight crack along a plasterboard joint is the tape case. British Gypsum's White Book treats joints as something you reinforce for crack resistance. Checkatrade's advice is mesh on anything wider than a hairline, then filler over the tape. Soudal's manufacturer information limits that acrylic filler to static joints. The amazon.co.uk bullets do not print a movement figure, so this page does not invent one. Use the cartridge only where the joint is already still, and only if you own a gun.
When filling again will fail
A second failure is information. If you filled a hairline properly, in a shallow key, and it reopened, the ceiling is moving or the background is loose. Checkatrade's plain stop is not to keep filling a crack that returns. Look for a stain that is brown or growing, a sag, a drumming sound, or a crack that runs from a corner and widens. British Gypsum's White Book says not to skim a damp wall. A ceiling stain after rain is a leak until a roofer or a plumber shows it is an old mark that is bone dry and not spreading.
Hollow plaster beside the crack means the skim has left the lath or the board. Sagging is the same family. Those are plasterer jobs. Textured coatings on older ceilings are a separate stop. If the texture might be old enough to need checking, do not sand it. For a crack that is still, shallow, and dry, a fine filler is enough. For a corner, caulk. For a straight joint wider than a hairline, tape then filler. For a stain, a sag, a hollow, or a line that already came back, stop.
Common questions
Should I rake out a hairline?
Open it slightly so the filler has a shoulder, which is the Which? prep for painting a room. A shallow V is enough. You are not cutting a deep channel, and you are not opening it so wide that a 3 mm fine filler has to plug a joint. Dust the groove before you fill. If the crack is already wider than a hairline and runs dead straight, you are in tape territory, not in a deeper rake.
Filler or caulk on a ceiling?
Filler on a hairline in the flat of the ceiling, if the line is still and dry. Decorator’s caulk where the ceiling meets the wall, or next to timber, because those junctions move. Which? warns off silicone there, because silicone usually will not take emulsion. Do not caulk a crack in the middle of the ceiling and expect it to act like a skim. Mesh is for a ceiling line that is more than a hairline, especially a board joint.
What about the crack where the ceiling meets the wall?
That corner is a caulk joint, not a filler joint. The wall and the ceiling move differently, and a rigid plug cracks along the angle. Use decorator's caulk, tool it into the corner, and paint it when it is ready. Bostik's UK guidance is junctions such as skirting and ceiling lines, and not constant water. If the corner is also stained or the ceiling sags into the angle, find the leak before you seal the gap.
Why did the crack come back?
Because the background moved, or the first fill had nothing to grip, or both. A smear on a closed hairline often falls out. A correct fill that still reopens is movement until you prove otherwise. One Palace fine filler review of a fine ceiling crack that held is one household, not a test of your joists. Stop refilling the same line. Look for a joint, a leak, or hollow plaster.
Do I need scrim tape?
You need it when the crack is more than a hairline and follows a joint, which is Checkatrade's split, and when the White Book's logic applies: joints are reinforced so they resist cracking. Tape first, then a thin filler over the mesh. A still hairline in the middle of a solid plaster field does not need tape. Caulk does not replace tape on a flat board joint.
Can patching plaster stop a moving joint?
No. Patching plaster sets into a rigid gypsum patch. UK reviews of the Palace powder talk about a fast set and a hard sand, not about flexibility. A moving joint needs a material that can move, such as decorator's caulk at a corner, or tape across a board joint. More plaster will not glue a crack that is still working. If the joint is static and the hole is a patch rather than a line, the powder can be the right material.
When is it a plasterer rather than a tube?
When the crack has returned after a proper fill, when the ceiling sags, when the plaster drums over a wide area, or when a stain shows the structure is wet. A single still hairline on a dry, solid ceiling is a tube of fine filler. A map of cracks, a drop, or a leak is not. If an old textured coating is involved, stop and get it checked before anyone sands. A plasterer can cut back to sound material. A tub cannot.
Related pages
Sources
Public sources from the research digest, last checked on 22 October 2026. Shelf prices and star lines are the amazon.co.uk figures stored on 21 October 2026. The price band is this set, not a market average. No listing was lab-tested.
- BS EN 13279-1:2008, NBS (retrieved 21 October 2026)
- HSE: sanding plasterboard joints (retrieved 21 October 2026)
- HSE CIS36: construction dust (retrieved 21 October 2026)
- British Gypsum White Book, finishes (retrieved 21 October 2026)
- Palace Chemicals, patching plaster (retrieved 21 October 2026)
- Polycell: fill holes and cracks in walls (retrieved 21 October 2026)
- SikaWall all purpose ready mixed filler data sheet (retrieved 21 October 2026)
- Wickes: Thistle Multi Finish 25 kg (retrieved 21 October 2026)