How to fill cracks in plaster
Updated: 23 October 2026
The emulsion is open, the crack beside the window is still full of dust, and you are about to paint over it. How to fill cracks in plaster, on a sound interior wall, is a short sequence: clear the crack, press the filler in proud, wait for that product's own time, sand, then seal the patch before you paint the wall. The [dry fill comparison](/hub/diy-supplies/dry-fill) is where the eight listings and their paint-time claims sit. Peter F. used those captures and the Health and Safety Executive's note on gypsum dust on 21 October 2026. We did not fill a wall in a lab. A qualifying purchase can earn a commission at no extra cost to you.
The emulsion is open, the crack beside the window is still full of dust, and you are about to paint over it.
The emulsion is open, the crack beside the window is still full of dust, and you are about to paint over it. How to fill cracks in plaster, on a sound interior wall, is a short sequence: clear the crack, press the filler in proud, wait for that product's own time, sand, then seal the patch before you paint the wall. The dry fill comparison is where the eight listings and their paint-time claims sit. Peter F. used those captures and the Health and Safety Executive's note on gypsum dust on 21 October 2026. We did not fill a wall in a lab. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Paint-ready claim | Form | Mixing | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Sika Sika One Strike | Quick drying. No minute figure in the attributes | Ready-mixed paste | No mixing | 8.9 | about £7.90 | View offer |
| Best value |  Langlow Langlow fine surface filler | Touch-dry in 1–2 hours. Paint once cured | Ready-mixed paste | No mixing | 8.8 | about £2.50 | View offer |
| Alternative |  Toupret Toupret Interior Filler | 12–24 hours in the bullets | Powder | Mix to a paste. Ratio not on the listing | 8.6 | about £8.75 | View offer |
On this page
Make the crack able to hold filler
Filler does not bond to dust, loose plaster or flaking emulsion. Open a hairline enough to give the paste an edge. Toupret's hairline method is a light open-up, then a brush to clear the dust, then a flush fill when the crack really is a hairline. Surrey Painters describe opening a crack to about 2–3 mm, which is their practice, not a figure on every tub here.
Brush or vacuum the dust out. If the plaster is thirsty, dampen it so it does not suck the water out of the filler. If the plaster is dusty or crumbling, Toupret wants a hardener and 24 hours before you fill. A hollow tap, or a crack that lengthens while you rake it, means the wall is failing.
Fill and leave it proud
Load a flexible knife, press the filler across the crack so it is forced in, then leave the repair slightly proud of the wall. Flush on the day you fill leaves nothing to sand back, and a shrink leaves a groove. On a true hairline, Toupret's method is one pass taken flush.
One coat is allowed only when that product's sheet says so. Langlow's sheet is layers of not more than 3 mm. A buyer still filled a 1930s crater with Interior Filler in three stages. If you are using powder, mix only what you can place inside the working time. Interior Filler's UK sheet is 30–40 minutes, at 500 ml of water per 1 kg, and the amazon capture does not print that ratio.
Wait for the product, not for a slogan
The failure you can feel is a dry skin over a soft centre. One Strike reviewers describe it on deeper holes, including about 3 cm that was still soft after weeks. Painting that skin traps the soft paste. Press a fingernail into the middle of the repair. If it gives, wait, or take it out and fill in thinner layers.
A heated room at about 20°C is the condition the short times assume. One Strike's sheet quotes about 30 minutes at 20°C and 50% relative humidity, and the listing has no minute figure. A spare room with the heating off takes longer.
Sand, then seal, then paint the wall
Sand flush with the wall and feather the edges so the patch does not sit as a disc. Ventilate if you are sanding for hours, and do not dry-sand a ceiling in a closed room and then sweep.
Bare filler is more porous than the emulsion around it, so the first coat flashes dull. Surrey Painters spot-prime, and they mention a mist coat diluted by about 10–20%, which is their practice, not a ratio on these listings. Seal the patch, then paint the wall. Stop when the crack reopens, the plaster is blown, or you are about to cut where cables may run. The choice of tub is the wall filler buying guide. A void behind the board is fill holes in plasterboard.
Common questions
How long do I wait before paint on these products?
Use the line for the tub you bought. Quick Fill and Fome Flex say about 30 minutes in the title or bullets. Decex says surface dry in 1–2 hours. Langlow says touch-dry in 1–2 hours, then paint once cured. Interior Filler and the 10 kg Toupret paste say 12–24 hours. One Strike's listing has no minute figure. Cold and deep fills take longer than the headline.
Why does the patch look dull after emulsion?
Filler is more porous than the surrounding paint, so the first coat sinks in and flashes dull or flat. Seal the patch before you roll the wall. Surrey Painters use a spot primer and mention a mist coat at about 10–20% dilution as their own method. That percentage is not printed on these amazon listings. A sealed patch, then a full wall coat, is what hides the repair.
Can I sand a ceiling in a closed room?
A single screw hole, with a window open, is a small amount of dust. Sanding taped joints or a whole ceiling in a closed room is the exposure the Health and Safety Executive writes about: gypsum dust, a workplace limit of 4.0 mg/m³ over 8 hours, and extraction on the tool. Do not dry-sand for hours and then sweep the pile into the air. Ventilate, and stop if you are reproducing a site job in a bedroom.
What if the middle is still soft?
You waited on the skin, not on the fill. Deep One Strike repairs in the review file skinned over and stayed soft, and one buyer scraped out holes about 3 cm deep after weeks. Take the soft material out and refill in layers the sheet allows, or wait until a fingernail in the centre meets a hard set. Painting over the skin locks the soft centre in place.
When is this no longer a filler job?
When the crack keeps growing, the plaster sounds hollow or is blowing off, the board is soft from a leak, or a ceiling needs a new panel. Damp and mould need the cause removed before any filler. If you are about to cut plasterboard and you do not know where the cables are, stop. A rigid filler in a moving skirting gap will also crack. That joint wants a flexible sealant, not another skim of paste.
Related pages
Sources
Public UK sources and the amazon.co.uk listings compared on this page. Updated 22 October 2026.
- Toupret: powder or ready-to-use filler (retrieved October 2026)
- Toupret Interior Filler sheet (retrieved October 2026)
- Toupret Quick Fill (retrieved October 2026)
- Sika Everbuild One Strike sheet (retrieved October 2026)
- Palace Langlow fine surface filler sheet (retrieved October 2026)
- HSE: sanding taped plasterboard joints (retrieved October 2026)
- DIY Guides: choosing the right filler (retrieved October 2026)
- Toupret: how to fix holes in plasterboard (retrieved October 2026)
- Consumer Rights Act 2015 (retrieved October 2026)