Skim a patch of wall with finishing plaster — HomeGraft

Patch and skim a damaged wall section from bare surface to a smooth, paintable finish in one session.

AB-01Assess the damage and mark out the patchLook at the crack, hole or blown plaster. Tap the area with a knuckle — anything hollow, crumbly or loose needs cutting back to sound material, not just filled over the top. Pencil a neat line a bit bigger than the damage so you have a clean edge to work to.

AB-02Work out what wall type you're dealing withTap the wall around the patch. Solid brick or block sounds dull and solid all over. A hollow, drum-like sound means plasterboard on a stud wall or dot-and-dab. Run a stud detector or a magnet across the surface to find a line of fixings — timber studs sit at roughly 400-600mm centres. Drill a small pilot hole in an area you'll cover anyway: pale wood dust means a timber stud, fine grey swarf means a metal stud, and a dusty grey powder that clunks after about 10-20mm of dust means dot-and-dab on masonry. Older houses (pre-1930s) may have lath and plaster — thin timber strips behind a lime plaster that feels springy when pressed.

1 each · Stud detector

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AB-03Check for cables and pipes, and know how to isolate themCables and pipes can run almost anywhere in a wall, not just in the usual safe zones — and a detector can still miss cables that are deep, in metal conduit, or behind metal-backed board, and metal studs confuse cheap detectors further. Sweep the whole patch with a cable and pipe detector, then drill or cut carefully as if something is still there. Find your stopcock (usually under the kitchen sink) and check it turns before you start, so you can shut off the water fast if you hit a pipe. If you have any doubt about what's behind the wall, isolate the relevant circuit at the consumer unit before drilling or cutting.

1 each · Cable and pipe detector

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AB-04Cut back to a sound, stable edgeOn solid brick or block, chip away loose or crumbling plaster with a bolster chisel and hammer until you reach firm masonry, then brush out dust. On plasterboard (timber or metal studs, or dot-and-dab), cut the damaged section out square with a plasterboard saw or utility knife, back to the nearest studs or dabs so you have something solid to fix a patch to. On lath and plaster, cut back to sound plaster only — if the timber laths themselves are broken, you'll need a bigger repair using expanded metal lath, not a simple skim.

1 each · Bolster chisel

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1 each · Plasterboard saw

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AB-05Fix a new patch of plasterboard if you've cut a holeCut a plasterboard offcut to match the thickness of the existing board (usually 12.5mm) and the shape of the hole. Into a timber stud, drive plasterboard screws into the centre of the stud at roughly 150mm spacing — never at the edge where the wood is narrow. Into a metal stud, use self-tapping metal-stud screws; a plain wood screw or wall plug will strip straight through 0.5mm steel and won't hold. On dot-and-dab, don't screw into the void behind the board — instead bed the patch onto fresh dabs of plasterboard adhesive pressed against the masonry, propped level until it grips. On lath and plaster, fix a piece of expanded metal lath across the gap, screwed or tied to the sound timber laths either side, as a base for the new plaster.

1 sheet · Plasterboard offcut (12.5mm)

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20 each · Plasterboard screws (32mm)

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10 each · Metal-stud self-tapping screws

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1 bag · Plasterboard adhesive (dot-and-dab)

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1 sheet · Expanded metal lath

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AB-06Prepare the surface and seal the edgesOn solid brick or block, brush off dust and apply a coat of diluted PVA (roughly 1 part PVA to 4 parts water) to control suction before plastering. On plasterboard patches, press self-adhesive scrim tape over every joint between old and new board so the join doesn't crack later. On lath and plaster, brush off loose debris and dampen the old plaster lightly so it doesn't pull the moisture out of the new coat too fast. Let PVA go tacky (touch-dry, not wet) before plastering over it.

1 litre · PVA bonding agent

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1 roll · Self-adhesive scrim tape

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AB-07Build up a base coat if the patch is deepIf the hole is deeper than about 10mm, don't try to fill it in one go with finishing plaster. Mix browning (bonding) plaster to a firm, non-slip consistency and apply in a layer up to about 10mm thick, scratching the surface with a scratch comb or the edge of a trowel once it's firm enough to hold a key. Leave it to go hard (usually 1-2 hours) before skimming over it.

1 bag · Browning (bonding) plaster

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1 each · Mixing bucket

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AB-08Apply the first coat of finishing plasterMix multi-finish plaster to a smooth, thick-cream consistency — small batches only, as it starts to go off within about 90 minutes. Load the hawk and apply a thin coat, roughly 2-3mm, over the whole patch with a plasterer's trowel, working from the edges inward. Don't worry about a perfect finish yet; this coat is about coverage.

1 bag · Multi-finish plaster

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1 each · Plasterer's trowel

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1 each · Hawk

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AB-09Apply a second thin coat and true up the edgesOnce the first coat has firmed up but is still slightly damp (usually 20-40 minutes later), apply a second, thinner coat of the same plaster. Feather the edges out into the surrounding wall with light trowel strokes so there's no visible ridge once it's painted. Check flatness across the patch with a straightedge or spare batten and fill any low spots.

AB-10Trowel and polish the surfaceAs the plaster starts to go off (it loses its shine), lightly mist it with clean water from a spray bottle and pass the trowel over it firmly to close the surface and bring up a smooth, polished finish. Do two or three light passes rather than one heavy one — pressing too hard too early drags the plaster and leaves marks.

1 each · Spray bottle

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AB-11Let it dry fully before checking and finishingLeave the patch to dry naturally for 2-3 days — don't use heaters or fans to speed it up, as this can cause cracking. Once fully dry (it changes from dark pink-grey to a lighter, even colour), run a hand or straightedge over it to check for high spots. Only sand lightly if needed; a well-trowelled skim shouldn't need much.

1 each · Fine sanding sponge

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AB-12Mist coat, then clean upBefore painting, seal new plaster with a mist coat — ordinary emulsion diluted roughly 70% paint to 30% water — so the final coats don't dry patchy. Scrape leftover plaster off tools before it hardens and wash them in a bucket, not down the sink; plaster sets in pipes and blocks them. Sweep up dust and offcuts, and lift dust sheets once everything is dry.

1 litre · Emulsion paint (for mist coat)

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1 each · Dust sheet

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