Paint over a damp patch once the cause is fixed — HomeGraft

Check the damp is truly gone, treat staining, then fill, prime and repaint the patch to match the wall.

PD-01Confirm the cause is fixed and the wall is dryDo not paint over a damp patch until the actual cause — a leak, blocked gutter, bridged cavity, rising damp — has been fixed and the wall has had time to dry out. Masonry dries slowly: as a rough guide allow a month of drying time for every 25mm of wall thickness. If the patch still feels cold, feels damp to the touch, or a cheap damp meter still shows a high reading, wait longer.

1 each · Budget damp meter (optional)

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PD-02Check the wall type and how badly it's damagedOn solid brick or block, tap the plaster near the patch — a dull, hollow sound means the plaster has blown and needs hacking off and re-plastering, not just painting. On plasterboard, whether on timber studs, metal studs, or dot-and-dab, press the patch gently — if the board has gone soft, swollen or crumbly, it has to be cut out and replaced, painting over it will not last. On lath and plaster, tap the same way: a bouncy or hollow patch means the plaster key has failed and the ceiling or wall needs proper repair, not decoration.

PD-03Clear the area and protect surfacesMove furniture away from the wall and lay dust sheets over the floor and anything nearby. Open a window for ventilation, since some of the products used later have strong fumes. Wear a dust mask and gloves before you start scraping.

1 each · Dust sheet

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1 pack of 5 · Disposable dust mask (FFP2)

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PD-04Strip off loose paint and any salt depositsScrape away any flaking, blistering or peeling paint with a stripping knife until you reach sound, firmly attached material. If you see white, crusty crystals on the surface, that's efflorescence — salts left behind by the damp. Brush them off dry with a stiff brush; do not wash them off, as water will draw more salts to the surface.

1 each · Stripping knife

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1 each · Stiff wire or nylon brush

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PD-05Fill any cracks or small holesFill any cracks, chips or small holes left by the scraping with a standard interior filler. Push it in firmly with a filling knife, slightly overfilling, and leave it to cure fully following the tin's timings before sanding.

1 each · Interior filler (small tub)

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1 each · Filling knife

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PD-06Sand the patch and feather the edgesSand the whole patch, including the filled areas, with medium then fine sandpaper. Feather the edges out into the surrounding wall so there is no visible ridge once painted. Wipe away all dust with a damp cloth and let the wall dry fully before continuing.

1 pack · Sandpaper (medium and fine grit)

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1 each · Cloth

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PD-07Apply a stain-blocking primerOld damp stains and salts can bleed straight through ordinary paint even after the wall has dried, so this step matters. Apply an oil-based stain block or a specialist damp-seal paint over the whole patch and slightly beyond its edges, following the tin's coverage and drying time. Keep the window open, as these products have strong fumes, and leave to dry fully — usually 1-2 hours, but check the tin.

1 each · Stain block / damp seal primer (250ml-1L)

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1 each · Paintbrush (50mm)

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PD-08Prime any bare plaster or fillerIf the filler or any bare new plaster is showing through the stain block, seal it first with a mist coat — matt emulsion thinned about 10% with water. This stops the topcoat drying patchy or flat in that spot. Let it dry fully before painting the topcoat.

1 each · Matt emulsion (for mist coat, small tester pot)

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PD-09Paint the topcoat to match the wallCut in around the edges of the patch with a small brush, then roll the topcoat over the whole area in the same paint and finish as the rest of the wall. Apply at least two coats, letting each dry fully first, and feather the roller strokes out into the surrounding paint so the patch blends in.

1 litre · Matching emulsion paint

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1 each · Small roller and tray

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PD-10Clean up and keep an eye on the patchWash brushes and rollers, and wipe down tools before they dry stiff with paint. Dispose of scraped paint and filler waste in your normal household rubbish, not down the drain. Keep an eye on the patch over the following weeks — if staining reappears, the original damp problem has not actually been fixed.

1 small bottle · White spirit or brush cleaner (for oil-based primer)

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