Fit a wall-hung vanity unit to a lath and plaster wall

Fit a wall-hung vanity unit safely by finding solid backing behind lath and plaster, and reconnecting the plumbing without leaks.

VU-01Clear the area and gather your toolsTake everything off the old vanity unit and move bins, rugs and bath mats out of the way. Lay a dust sheet on the floor to catch plaster dust and dropped screws. Get your tools ready: a cordless drill with wood and masonry bits, a spirit level, pencil, stud/pipe detector, screwdriver set and an adjustable spanner.

1 each · Dust sheet

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1 each · Masonry/wood drill bit set

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VU-02Find your stopcock and test itBefore you disconnect anything, find your stopcock — it's usually under the kitchen sink — and turn it off and back on once to check it moves freely. You'll need to shut off the water fast if you catch a pipe while working. If it's stiff or won't turn, sort this out before starting any plumbing work.

VU-03Disconnect the old basin and isolate the waterTurn off the isolation valves under the old basin, then open the tap to release any pressure in the pipe. Undo the tap connectors and the waste trap with an adjustable spanner, catching leftover water in a bucket. Lift the old basin and unit away from the wall and set it aside.

1 each · Bucket

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VU-04Mark the height and fixing positionsHold the new unit or its wall bracket against the wall and mark the top edge with a pencil, checking it with a spirit level. A vanity top usually sits around 800-850mm from the floor, but check this clears your existing waste and supply pipes first. Mark through the bracket or unit's fixing holes onto the wall so you know exactly where to drill.

1 each · Pencil

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VU-05Work out what's behind the lath and plasterLath and plaster can be fixed to timber studs, or straight onto solid masonry with timber battens behind it, and this changes which fixing you need. Run a detector over the marked area, then look for a line of old nail or screw heads roughly 400mm apart — this usually marks a timber stud or batten. Tap the wall: a hollow sound between the marks means timber behind, a dull solid sound means masonry. If you find a metal track instead of timber, this isn't a typical lath and plaster wall — treat it as a stud partition and get proper metal-stud fixings, since a vanity is too heavy for these alone.

1 each · Stud/pipe detector

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VU-06Drill your test and fixing holes safelyCables and pipes can run almost anywhere behind a wall, not just in the usual safe zones — a detector helps, but it can miss cables that are deep, in metal conduit, or behind old metal lath, so always assume something's there until you've proved otherwise. Drill a small 3mm pilot hole first at each marked point: timber dust means a stud or batten, pale grainy dust means masonry, and bright metal swarf or sudden resistance means stop immediately. If you have any doubt at all, isolate the electrics for that area at the consumer unit before drilling, and make sure your stopcock is off before cutting or drilling any deeper near existing pipework.

1 each · 3mm drill bit

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VU-07Fit a noggin if you're fixing into a timber stud wallIf your pilot holes show timber studs but they don't line up with your marked fixing points, you'll need a noggin. Cut a neat section of the lath and plaster away between two studs with a small saw, keeping the hole just big enough to work in. Screw a piece of 47x50mm timber noggin horizontally between the studs at the right height, then patch the plaster back with plasterboard and filler before fixing the unit. Skip this step if solid masonry sits behind the lath instead.

1 each · Timber noggin (47x50mm)

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1 each · Plasterboard patch offcut

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4 each · Wood screws (75mm)

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VU-08Choose and fit the right fixing for your wallFor a timber stud or noggin, use two or three 75mm coach screws driven into the centre of the timber, pre-drilling a 4mm pilot hole so the wood doesn't split. For solid masonry behind the lath, drill through the plaster and batten into the brick or block with a 10mm masonry bit to at least 60mm depth, then fit heavy-duty masonry sleeve or resin anchors rated for the vanity's weight plus someone leaning on it. Never rely on lath and plaster alone to hold a wall-hung vanity — the fixing must reach solid timber or masonry behind it. Wipe out drilled holes before fitting anchors so they seat properly.

3 each · Coach screws (75mm)

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3 each · Masonry sleeve anchors (M10)

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1 each · 10mm masonry drill bit

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VU-09Mount the unit and check it's levelWith a helper if the unit is heavy, lift it onto the fixings and push it fully home against the wall. Check it's level side to side and front to back, and tighten every fixing fully before letting go. Give the unit a firm push and pull test by hand to check it doesn't move.

VU-10Reconnect the tap and wasteFit new tap connectors and reconnect the waste trap, using PTFE tape or a fibre washer on any threaded joints. Tighten compression or push-fit joints as needed, following your fitting's instructions, and don't overtighten plastic fittings. Keep the isolation valves off until every joint is done.

1 each · PTFE tape

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2 each · Tap connectors

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2 each · Fibre washers

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VU-11Turn the water back on and check for leaksOpen the isolation valves slowly and turn the tap on and off a few times to clear air from the pipe. Check every joint you touched for drips, using a dry sheet of tissue to spot small leaks that aren't obvious by eye. Tighten anything that's damp a quarter turn at a time and recheck.

VU-12Tidy up and finishRun a bead of bathroom silicone sealant along the join between the vanity top and the wall to stop water getting behind it. Wipe away excess sealant with a damp cloth before it skins over. Fold up your dust sheet, sweep up any plaster dust, and dispose of the old unit and packaging.

1 each · Bathroom silicone sealant

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