Repair a hole in a lath and plaster wall

Patch a hole in a lath and plaster wall by cutting back to sound material, fitting new backing and finishing with plaster.

AB-01Clear the area and set up safety kitMove furniture away from the wall and lay a dust sheet on the floor. Wear a dust mask, safety goggles and gloves — old lime plaster and lath dust is unpleasant to breathe and can irritate skin. Find your stopcock, usually under the kitchen sink, and check it turns freely so you can shut the water off fast if you hit a pipe later. Locate your consumer unit too, so you know exactly where to isolate the circuit if you need to.

1 each · Dust sheet

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1 each · FFP3 dust mask

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1 each · Safety goggles

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1 pair · Work gloves

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AB-02Check for asbestos before you disturb old plasterLook closely at the surface around the hole. If it's a textured coating, or you don't know when the wall was last decorated and it could be pre-2000, treat it as suspect. Don't sand, drill or scrape it dry until it's been checked. Lime plaster and horsehair itself isn't asbestos, but old paint or skim coats sometimes are.

RULES

1 each · Asbestos test kit (optional)

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KNOW THE RULES

Under the Control of Asbestos Regulations 2012, some textured coatings and old finishes applied before 2000 may contain asbestos. If in doubt, get a sample tested by a UKAS-accredited lab or call in a licensed asbestos specialist before disturbing it.

AB-03Find the studs and confirm what you're fixing intoRun a stud detector or a strong magnet either side of the hole; a magnet catches on the heads of nails holding the laths, showing you where the timber studs or battens run. Tap the wall — a dull, solid sound means a stud, a hollow sound means the gap between laths. Lath and plaster is fixed to timber, never metal studs or dot-and-dab, so if a pilot hole brings out fine steel swarf instead of wood dust, you've found a later repair with a different build — stop and reassess before going further. Mark the centre of each stud with a pencil so your patch and noggin line up properly.

1 each · Stud detector or magnet

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1 each · Pencil

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AB-04Cut back to sound materialCables 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 conduit, or hidden behind old metal lath. If there's any doubt at all, isolate the relevant circuit at the consumer unit before you drill or cut, and make sure your stopcock is off before cutting into anything that could hide a pipe. Use a padsaw or sharp utility knife to cut the loose, crumbling plaster and broken laths back to a neat square, stopping at the nearest sound studs on each side. Remove all debris until you're only fixing to solid material.

1 each · Padsaw

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1 each · Utility knife

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1 each · Rubble bucket

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AB-05Fit a timber noggin for supportCut a length of 45x25mm timber batten to span between the two nearest studs behind the hole. Screw it to the back face of each stud using 4x40mm wood screws driven into the centre of the timber, never near the edge, where it can split. This gives the new patch a solid fixing point along its top and bottom, not just at the sides. If you ever find metal stud framing instead of timber here — rare with lath and plaster, but possible after a partial rebuild — never use a wood screw or plastic wall plug; it will strip straight through 0.5mm steel. Use a self-drilling metal-stud screw instead, and remember a stud alone should never carry anything heavy or anything that pulls away from the wall; that needs a proper noggin or a fixing back to solid material.

1 each · Timber batten 45x25mm, 1m

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8 each · Wood screws 4x40mm

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AB-06Cut and fix a plasterboard patchMeasure the hole and cut a piece of 12.5mm plasterboard to fit, leaving a 2-3mm gap all round so filler can key into the edges. Fix the patch with 32mm plasterboard screws every 150mm into the studs and the new noggin, driving the head just below the paper face without tearing it. Check the patch sits flush with the surrounding plaster, packing it out slightly with cardboard shims if it's more than a couple of mm proud or recessed.

1 each · Plasterboard offcut, 12.5mm

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20 each · Plasterboard screws 32mm

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AB-07Tape the joints with scrimStick self-adhesive scrim tape over every joint between the new patch and the old lath and plaster, pressing it down firmly with no bubbles or wrinkles. This stops the joint cracking later as the two different materials expand and move slightly against each other.

1 each · Scrim tape, 10m roll

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AB-08Apply the base filler coatMix a bonding coat, or use a ready-mixed multi-purpose filler, and spread a thin layer over the taped joints and patch with a plasterer's trowel or wide filling knife. Feather the edges out onto the surrounding old plaster so there's no visible ridge. Leave it to go off fully, usually a few hours, before moving on.

1 bag · Bonding coat plaster, 5kg

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1 each · Plasterer's trowel

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AB-09Apply the finish coat and blend it inOnce the base coat is hard, apply a thin finish coat of multi-finish plaster or fine surface filler over the whole patch, feathering it well beyond the edges into the surrounding wall. Work it smooth with a damp trowel or sponge float while it's still workable. Leave it to dry fully, which can take a day or two depending on thickness and ventilation.

1 bag · Multi-finish plaster, 5kg

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1 each · Sponge float

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AB-10Sand, prime and clean upOnce fully dry, sand lightly with fine abrasive paper to remove any ridges, then wipe away the dust with a damp cloth. Apply a mist coat of diluted emulsion or a proper plaster sealer before decorating, since new plaster is porous and drinks ordinary paint unevenly. Bag up rubble, old lath and dust sheets, and check the floor and skirting for stray nails or debris.

1 pack · Fine sandpaper, 120 grit

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1 each · Plaster sealer or mist coat paint, 1L

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1 each · Rubble sack

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