How to fix a crack in a ceiling

Video by Proper DIY. This walk-through is based on the video "How to Fix Reoccurring Cracks in Walls or Ceilings for GOOD!" from the Proper DIY channel, which focuses specifically on cracks that keep coming back and how to stop them. The section on using jointing tape to bridge movement cracks is well worth watching before you start filling.

1. Work out what kind of crack you are dealing with

Not all ceiling cracks are the same. A hairline crack that has been there for ten years without growing is almost certainly just settlement — the building moved slightly when it was new, and the crack is a record of that. These are cosmetic. Fill them, paint them, done.

A crack that has appeared recently, is getting wider, or runs diagonally across the ceiling is a different matter. So is one that follows the line of a joist or plasterboard joint, which often means movement rather than just shrinkage. If a crack is more than about 5 mm wide, is accompanied by bulging plaster, or there is any suggestion of water getting in from above, get a professional to look at it before you fill anything. For everything else, carry on.

2. Open up the crack before you fill it

This is the step people most often skip, and it is the reason filled cracks come back. Run the edge of a scraper, a cold chisel, or even an old screwdriver along the crack to open it out slightly into a V-shape. You want to get below any loose edges and create a proper key for the filler to grip.

Brush out the dust and debris with a stiff brush, then wipe the area with a damp cloth. On older plaster ceilings, probe the area around the crack with your knuckle — hollow sounds mean the plaster has detached from the lath behind. If large sections are hollow, filling the crack is only a temporary fix; that area of ceiling will need to be cut back and replastered or overboarded.

3. Apply a PVA bonding coat first

Old plaster is porous and will suck the moisture out of any filler you apply before it has had a chance to bond. Dilute some PVA adhesive (about 1 part PVA to 4 parts water) and brush it generously into and around the crack. Let it go tacky — not fully dry, just sticky to the touch. Then apply your filler while the PVA is still working.

This step makes a real difference on older properties. To be fair, on a modern plasterboard ceiling with an intact surface you can often skip it, but on Victorian and Edwardian plaster — common enough in Sandwich — the PVA is what keeps the repair in place long term.

4. Use jointing tape for cracks that keep returning

For cracks along plasterboard joints, or any crack that has been filled and come back more than once, paper jointing tape is the answer. Bed the tape into a layer of jointing compound or a flexible filler while it is wet, smooth it flat, and let it dry. The tape bridges the crack and prevents it from reopening with seasonal movement.

Cut the tape slightly longer than the crack, press it in firmly, and work out any air bubbles with the edge of your filling knife. Once dry, apply a thin skim of filler over the top to bring it flush with the surrounding ceiling. Fine-grade finishing filler works best for this second coat — it sands more easily than all-purpose filler.

5. Sand and feather the repair flat

Once the filler is completely dry — not just dry on the surface but hard all the way through — sand it back with 120-grit paper on a sanding block. Work in circular motions to blend the edges of the repair into the surrounding plaster. Then switch to 180- or 220-grit to finish. The aim is to get the repair so flat that you cannot feel it when you run your hand across the ceiling.

Hold a torch at a low angle across the surface to pick up any ridges or hollows. This raking light shows up imperfections that look invisible in normal lighting but will be obvious once the ceiling is painted. Better to find them now and fill again than to discover them after you have rolled two coats of emulsion over everything.

6. Prime the repair before painting

Bare filler is absorbent and will show through emulsion as a dull patch — you can see exactly where the repair was even after painting, which defeats the whole point. Apply a coat of diluted emulsion or a proprietary mist coat (emulsion thinned about 10% with water) to the repaired area first. Let it dry, then apply your ceiling paint over the whole area.

Two full coats of ceiling white should be enough to blend the repair in. If you can still see it, it usually means the filler was not sanded flat enough rather than a paint problem. One final tip: roll, do not brush, for the finishing coats. A brush leaves stipple marks that catch the light differently from the rest of the ceiling and the repair never fully disappears.

When to call a handyman

Call Richard if the ceiling has multiple cracks across a large area, if plaster is lifting or bulging anywhere, or if you are simply not keen on working overhead for a few hours with filler dropping in your eyes. Ceiling repairs are one of those jobs that is surprisingly tiring to do yourself — having someone else do the prep, tape, fill, sand, and mist coat is often well worth a call.