Fill cracks and holes before painting

Rake out, fill and seal cracks and holes correctly for your wall type before painting, so repairs don't reopen.

FC-01Clear and protect the areaMove furniture back, take down pictures and mirrors nearby, and lay dust sheets on the floor. Open a window for ventilation, and put on a dust mask and eye protection before you start scraping or sanding.

1 each · Dust sheet

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1 each · Dust mask

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1 each · Safety glasses

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FC-02Work out what's behind the crack or holeTap the wall near the damage. A solid, dull thud usually means brick or block behind (solid masonry, or dot-and-dab where you happen to hit a dab). A hollow, drum-like sound means plasterboard on studs. A springy, slightly bouncy feel, especially on a ceiling, points to lath and plaster. This tells you which filler to use in the next steps.

FC-03Rake out and clean the damageUse a filling knife or scraper to open a hairline crack slightly and undercut the edges, so it's wider at the back than the front. This gives the filler something to grip. Brush out dust and loose material, then wipe with a slightly damp sponge, since filler won't stick to dusty edges.

1 each · Filling knife

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1 each · Scraper

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1 each · Stiff brush

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1 each · Sponge

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FC-04Choose flexible or rigid filler for your wall typeOn solid brick or block plaster, a plain hairline shrinkage crack won't move, so ordinary multi-purpose filler is fine. On plasterboard walls or ceilings, whether on timber or metal studs, and on dot-and-dab, cracks often follow board joints and reopen with normal seasonal movement, so use a flexible decorators' caulk instead of a rigid filler. On lath and plaster, treat any wide, stepped, or soft-feeling crack as a sign the plaster key may be loosening from the laths behind, not just cosmetic, and get it checked before you paint over it.

1 tub · Multi-purpose filler

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1 tube · Flexible decorators' caulk

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FC-05Bridge wider cracks and joints with scrim tapeFor any crack wider than a hairline, or one running along a plasterboard joint (common on stud walls and dot-and-dab), press a strip of self-adhesive scrim tape over it first. This bridges the gap so the filler on top has continuous support instead of just bridging thin air.

1 roll · Self-adhesive scrim tape

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FC-06Fill shallow cracks and small holesLoad a flexible filling knife with filler and draw it across the crack, pressing firmly so filler goes into the gap, then draw the blade off flat. Leave the fill slightly proud of the surface, since most fillers shrink a little as they dry.

FC-07Fill deeper holes in layersFor holes deeper than about 5mm, such as old fixing holes, fill in thin layers and let each one go off before adding the next, rather than one thick fill that can crack or slump. If a hole on a stud or dot-and-dab wall goes right through to the cavity, push in scrunched newspaper or a small offcut of plasterboard first as backing, so the filler has something solid to sit on.

1 tub · Multi-purpose filler

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1 each · Plasterboard offcut

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FC-08Leave the filler to dry fullyCheck the drying time on the tub or tube. Shallow fills usually take a few hours, but deep or layered fills need overnight. Don't rush this step, since painting over damp filler causes it to shrink and crack again later.

FC-09Sand smoothOnce completely dry, sand with fine 120 to 180 grit sandpaper or a sanding sponge, working the filler flush with the surrounding wall or ceiling. Wipe away all dust with a slightly damp cloth before you go anywhere near paint.

1 pack · Sandpaper (mixed grit pack)

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1 each · Sanding sponge

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1 each · Cloth

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FC-10Seal the filled patches before paintingFiller is more porous than the surrounding wall and will show through as a dull, flat patch under paint if left unsealed. Brush a coat of diluted emulsion or a proper sealer over each filled area and let it dry before painting the whole wall or ceiling.

1 each · Diluted emulsion or sealer

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1 each · Small brush

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FC-11Clear upVacuum or sweep up dust and debris, wipe down nearby surfaces, and wash tools in water while any filler on them is still wet. Press the lid firmly back onto leftover filler and caulk so they don't dry out before the next job.

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