Patch a large hole in plasterboard — HomeGraft

Cut back a plasterboard hole to sound board, support it properly, then patch, tape and fill for an invisible repair.

PH-01Clear the area and protect your floorMove furniture clear of the wall and lay a dust sheet underneath the work area. Vacuum loose plaster dust out of the hole and snap off any crumbling edges by hand so you're left with sound, firm board. Keep a dust mask and safety glasses to hand for the cutting stage.

1 each · Dust sheet

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1 pack · Disposable dust masks

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PH-02Work out what's behind the holeRun a magnet or stud detector either side of the hole and follow the line of screw heads to find a timber or metal frame; a hollow sound between hits usually means studs spaced 400mm or 600mm apart. Drill a small pilot hole at the edge of the damaged board: fine pale dust means timber, bright metal swarf means a metal stud track. A dead, solid knock right across the wall means plaster straight onto brick or block. A hollow sound almost everywhere except narrow vertical strips every 300-450mm means dot-and-dab plasterboard. A crumbly, springy knock with thin wooden strips visible behind the hole means lath and plaster.

1 each · Stud detector

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PH-03Check for cables and pipes before you cut or drillCables and pipes can run almost anywhere in a wall, not just in the usual safe zones, so sweep a cable and pipe detector over the whole repair area first. Treat a clear reading as a guess, not a guarantee — detectors miss deep cables, cables in metal conduit, anything behind metal-backed plasterboard, and metal stud frames confuse cheap detectors further. Find your stopcock (usually under the kitchen sink) and check it turns before you start, so you can shut the water off fast if you nick a pipe. If you have any doubt at all, isolate the circuit at the consumer unit before drilling, and turn the water off at the stopcock before cutting into anything that could carry water.

1 each · Cable and pipe detector

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PH-04Cut the damaged area back to a clean rectangleMark a neat rectangle or square around the hole, keeping every side straight and square. Where you can, line the vertical cuts up with the centre of a stud using the line you found in step 2, so you have solid timber or metal to screw into later. Cut along your lines with a plasterboard saw or sharp utility knife and lift out the damaged piece.

1 each · Plasterboard saw

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1 each · Utility knife

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1 each · Metal ruler or straight edge

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PH-05Fit support behind the patchHow you support the patch depends on what's behind it. Timber stud wall: screw a 25x50mm timber batten to the exposed studs with 40mm wood screws so it sits flush behind any cut edge that isn't already on a stud. Metal stud wall: fix the same batten to the metal track with self-drilling metal-stud screws — never wood screws or plastic wall plugs, which strip straight through 0.5mm steel. Dot-and-dab wall: screw a batten across the gap and fix it back through to the solid masonry behind the dabs, using a wall plug and screw long enough to pass through the board, the void, and at least 30mm into the brick or block (usually 60-75mm overall). Solid brick or block with plaster straight onto masonry: fix the batten directly into the wall with a suitable plug and screw, no noggin needed. Lath and plaster: don't rely on the laths, they're thin and will split; screw a batten to the timber studs or joists behind instead, the same way as for a timber stud wall.

2 each · Timber batten 25x50mm, 600mm length

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1 box · Wood screws 40mm

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1 box · Self-drilling metal stud screws

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1 box · Wall plugs and screws (masonry, 60-75mm)

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PH-06Cut and fix the patchCut a piece of plasterboard to match the hole exactly, using the same thickness as the existing board (usually 12.5mm). Fix it to the battens or studs with 32mm drywall screws every 150-200mm around the edge, driving the heads just below the paper face without tearing it.

1 each · Plasterboard offcut, 12.5mm

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1 box · Drywall screws 32mm

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PH-07Tape the jointsCover every joint between the new patch and the old board with self-adhesive scrim tape, pressing it flat with no bubbles or gaps. Overlap the corners neatly so the tape can't lift once you start filling.

1 roll · Scrim tape

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PH-08Fill the joints in thin coatsApply a thin layer of joint filler over the taped joints with a filling knife, feathering the edges well beyond the tape so there's no ridge. Let it dry fully, then apply a second, wider coat to build up a smooth, flat surface. Repeat a third time if you can still see or feel the joint line.

1 tub · Joint filler / joint compound

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1 each · Filling knife

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PH-09Sand smoothOnce fully dry, sand the filled area with fine abrasive paper (120-180 grit) until it's flush with the surrounding wall — check with your hand and a raking light rather than just your eyes. Wipe away dust with a slightly damp cloth before painting.

1 each · Fine sandpaper or sanding sponge

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PH-10Seal, prime and tidy upApply a mist coat (diluted emulsion) or a proper drywall primer over the repaired area so it takes paint evenly — bare filler is porous and will flash through the finished paint if you skip this. Once dry, repaint the wall as needed. Fold up dust sheets, vacuum any debris, and bin the offcuts and packaging.

1 L · Drywall primer or diluted emulsion for mist coat

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