Preparing a surface for paint

Learn to clean, fill, sand and check a wall so paint sticks properly and looks smooth.

PS-01Clear the area and protect the floorMove furniture back and lay down an old sheet or dust sheet. Preparing a wall for paint always makes dust and drips, even if you're careful. Skipping this step is the beginner mistake that leads to filler dust ground into a carpet.

PS-02Wash the surface with sugar soapSugar soap is a mild cleaning solution sold for pre-paint cleaning. Mix it with water as the label says, then wipe the whole surface with a sponge to lift off grease, cooking residue and general grime. Paint won't grip properly over grease, even if the wall looks clean to the eye.

1 bottle · Sugar soap

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PS-03Check for flaking or loose paintRun your hand flat over the surface and press gently in a few spots. Any paint that flakes, bubbles or feels soft needs scraping back with a filling knife (a flat, flexible blade) until you reach solid, firmly stuck paint or bare plaster. Painting over loose paint just means it peels again later, taking your new coat with it.

PS-04Fill holes, cracks and dentsUse a filling knife to press ready-mixed filler into any hole or crack, slightly overfilling so it sits a little proud of the surface. Leave it to dry fully - times vary but rushing this is the classic mistake, since wet filler sands into a smear instead of a powder. If a crack is deep, build it up in two thin layers rather than one thick one, letting each dry first.

1 tub · Ready-mixed filler

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PS-05Sand the surface to key itKeying means dulling a shiny surface slightly so new paint has something to grip. Use medium-grit sandpaper (around 120-grit) on a sanding block, and sand dried filler flush with the wall using light, even strokes. On old gloss paintwork, especially in a house built before the 1960s, wear a dust mask and dampen the surface slightly first, since old paint can contain lead and sanding it dry creates fine dust you don't want to breathe in.

1 sheet · Sandpaper, 120-grit

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PS-06Wipe away all dustUse a damp cloth (just damp, not wet) to wipe the whole surface, rinsing and re-wetting the cloth as it picks up dust. Any dust left behind ends up stuck in your paint film as a rough patch. Let the wall dry fully before painting - a few minutes is usually enough.

PS-07Check you've done it rightRun your flat hand slowly over the whole surface in good light. It should feel smooth with no grit, no ridges where filler meets wall, and no shine from grease. Shine a torch across the surface at a low angle - this shows up bumps and dips that normal light hides, so you can catch them before you paint, not after.

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