Replace a damaged sheet of plasterboard — HomeGraft

Cut out a damaged plasterboard section, fit a new patch safely, then fill and sand it invisible.

PB-01Check the damage and mark your cut-back lineLook at how far the damage spreads. Draw a rectangle around it in pencil, extending each side to the centre of the nearest stud, joist or noggin, so the new patch has something solid to fix to. On a ceiling, do the same but line up with joists. If the wall is lath and plaster, expect the damage to run further than it looks — old laths crack easily once disturbed.

1 each · Pencil

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1 each · Spirit level or straight edge

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PB-02Gather your tools and materialsLay everything out before you start cutting: dust sheets, PPE, cutting tools, screws and filler. Match the new board's thickness to the old one — 12.5mm is standard for walls, 9.5mm for many ceilings.

1 each · Plasterboard sheet or offcut (12.5mm)

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1 each · Plasterboard saw or utility knife

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1 each · Dust sheet

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1 set · Dust mask and safety glasses

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PB-03Work out what's behind the surfaceRun a stud detector or a magnet across the wall — a line of regularly spaced screw heads or magnetic hits means a stud wall. Tap between hits: a hollow, papery sound is plasterboard on studs, a solid dead thud is solid brick or block, or dot-and-dab over masonry. Drill a small pilot hole in an inconspicuous spot — fine pale dust means timber studs, grey brick dust means masonry, and bright metal swarf means metal studs. Dot-and-dab boards feel slightly springy and sit a little off the wall; lath and plaster feels uneven and, once you cut in, shows narrow horizontal wooden strips.

1 each · Stud detector or magnet

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1 each · Cordless drill with small pilot bit

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PB-04Check for cables and pipes before you cutCables and pipes can run almost anywhere, not just in the usual 'safe zones' — a detector helps but can miss deep cables, metal conduit, or anything behind metal-backed board, and a metal stud frame can confuse a cheap detector further. Before you cut, find your stopcock (usually under the kitchen sink) and check it turns freely, so you can shut off the water fast if you hit a pipe. If you're at all unsure what's behind the board, isolate the relevant circuit at the consumer unit before cutting, and turn the water off at the stopcock if there's any chance of hitting a pipe.

PB-05Cut back to a supported edgeScore along your marked lines with a utility knife against a straight edge, then snap and cut through with a plasterboard saw. Stop each cut at the centre of the nearest stud, joist or noggin — never leave an unsupported floating edge. On dot-and-dab, cut only through the plasterboard itself; leave the adhesive dabs alone unless they're damaged too.

1 each · Utility knife

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PB-06Remove the damaged sectionLever the cut piece out with a small bar or the claw of a hammer, easing it forward and down rather than punching it inward. Check what's exposed behind — sound timber, sound metal studs, solid masonry, dabs of adhesive, or old laths. If you see any cable or pipe you weren't expecting, stop and check it's dead or isolated before going further.

1 each · Small pry bar

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PB-07Add support behind the opening if neededOn a timber stud wall or ceiling, if the cut edge falls between studs or joists, screw a timber noggin (38x38mm) across the gap so the patch has an edge to fix to. On a metal stud wall, fit a timber batten or metal noggin between the studs using self-drilling screws, not ordinary wood screws — wood screws strip straight through thin steel. On dot-and-dab, only add fresh adhesive dabs if the originals came away; otherwise leave the masonry behind as is. On lath and plaster, if the laths are too broken to hold a fixing, screw a timber batten between the joists or studs behind for the new patch to grip.

1 length · Timber batten/noggin 38x38mm

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10 each · Self-drilling screws for metal stud (25mm)

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

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PB-08Cut the new patch to sizeMeasure the opening exactly and mark it out on your new board. Cut it slightly undersized rather than oversized — a gap of 3-5mm is easier to fill than a board that won't fit. Lightly bevel the cut edges with the knife so the joint takes filler well, then dry-fit the patch before fixing anything.

PB-09Fix the new patch — method depends on the wall typeTimber stud: drive 3.5x40mm drywall screws into the centre of each stud and noggin at roughly 200mm centres, driving the head just below the surface without tearing the paper. Metal stud: use self-drilling drywall screws for metal stud at the same spacing — never a plain plastic wall plug or an ordinary wood screw, both strip straight through 0.5mm steel. Solid masonry (plaster removed to brick or block): drill 7mm holes and fit 6mm wall plugs at roughly 300mm centres, then screw the board on. Dot-and-dab: fix into any timber noggin or stud behind, or use fixings long enough (60-75mm) to reach the masonry through the adhesive cavity. Lath and plaster: screw into the joists or studs behind the laths, not the laths themselves, and don't overtighten.

20 each · Drywall screws 3.5x40mm

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20 each · Self-drilling screws for metal stud (40mm)

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8 each · Wall plugs 6mm

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8 each · Masonry screws 60-75mm

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PB-10Tape the jointsApply a thin layer of joint filler along each new joint, then bed paper or mesh joint tape into it with a taping knife. Smooth out any air bubbles or ridges while the filler is still wet, working from the centre outward.

5 m · Joint tape (paper or mesh)

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1 tub · Jointing/filler compound

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1 each · Taping knife

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PB-11Apply the first fill coatOnce the tape coat is fully dry, spread a wider layer of joint filler over the joints, feathering it out 150-200mm beyond the tape on each side. Leave it to dry fully, usually overnight, before touching it again.

PB-12Apply a second coat and feather the edgesApply a thinner finishing coat over the first, feathering it further out so the repair blends into the surrounding wall with no visible ridge. Let it dry fully before sanding.

PB-13Sand smooth and check the surfaceSand lightly with fine (120-150 grit) sandpaper, working in small circles rather than digging in one spot. Run a straight edge across the patch to check for flat, even ground, then wipe away dust with a damp cloth.

2 sheet · Fine sandpaper (120-150 grit)

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PB-14Tidy up and seal the patchClear away dust sheets and vacuum the area, including the floor and skirting. Apply a mist coat or a coat of primer over the repaired patch before decorating, so the new filler doesn't soak up paint unevenly.

1 litre · Mist coat/primer

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