Fit a wall-hung vanity unit to a dot-and-dab plasterboard wall — HomeGraft

Fit a wall-hung vanity safely by finding what is behind the board and using fixings strong enough to hold it.

VN-01Prepare the room and turn off the waterClear the area and lay dust sheets down. Find your stopcock — usually under the kitchen sink — and check it turns freely before you start. Turn off the isolators under the old basin if fitted, or the stopcock if not, then open the taps to drain the pipes into a bucket. Remove the old unit if you're replacing one, and clean the wall back to bare plasterboard.

1 each · Dust sheet

Buy:ScrewfixB&QToolstationAmazon

1 each · Bucket

Buy:ScrewfixB&QToolstationAmazon

1 each · Adjustable spanner

Buy:ScrewfixB&QToolstationAmazon

VN-02Work out what's behind the boardDot-and-dab plasterboard is glued to the masonry behind with adhesive dabs, leaving a 10–50mm gap, so it sounds mostly hollow with occasional solid thuds when you tap it. A true stud wall sounds hollow in a steady rhythm every 400–600mm with no masonry behind at all. Run a detector or a magnet along the wall — a steady line of screw heads means a stud, and no reading over a wide area suggests dot-and-dab on masonry. Drill a 3mm pilot hole to check: pale brick or block dust means masonry, pale timber-coloured dust means a wood stud, and fine bright swarf means you've hit a metal stud. In an older house it might be lath and plaster instead — thin timber strips under lime plaster — which won't hold a fixing on its own, so you'll still need to find the timber studs behind it the same way.

1 each · Stud, pipe and cable detector

Buy:ScrewfixB&QToolstationAmazon

1 each · Small magnet

Buy:ScrewfixB&QToolstationAmazon

1 each · 3mm drill bit

Buy:ScrewfixB&QToolstationAmazon

VN-03Choose the right fixings for what you findPlasterboard and dabs alone will never hold a vanity unit's weight, the basin, the water inside it and someone leaning on it — you need something solid. If masonry sits behind the dot-and-dab, use long fixings (M8 x 100–120mm frame fixings or resin anchors) that pass through the board, bridge the dab gap, and bite at least 40mm into the brick or block; drill with a 10mm masonry bit. If you find a timber stud wall, don't rely on one stud — screw a 12mm plywood pattress panel across at least two stud centres using 4mm x 50mm wood screws, then fix the unit to the pattress. If you find a metal stud wall, never use a plain wall plug or an ordinary wood screw — it strips straight through 0.5mm steel; screw a plywood pattress across at least two metal studs using self-drilling metal-stud screws instead. On lath and plaster, ignore the lath and fix into the timber studs behind using the same pattress method.

1 pack · M8 x 100mm frame fixings/resin anchors (pack of 4)

Buy:ScrewfixB&QToolstationAmazon

1 each · 10mm masonry drill bit

Buy:ScrewfixB&QToolstationAmazon

1 each · 12mm plywood pattress panel (approx 400x300mm)

Buy:ScrewfixB&QToolstationAmazon

1 pack · 4mm x 50mm wood screws (pack)

Buy:ScrewfixB&QToolstationAmazon

1 pack · Self-drilling metal-stud screws (pack)

Buy:ScrewfixB&QToolstationAmazon

VN-04Mark the fixing height and levelHold the vanity unit or its fixing template against the wall at the height you want — most units sit with the top around 800–850mm from the floor, but check the manufacturer's instructions first. Use a spirit level to draw a level horizontal line, then mark the fixing centres from the template or the back of the unit. Check every mark lines up with solid masonry, a stud, or the pattress area from the last step.

1 each · Pencil

Buy:ScrewfixB&QToolstationAmazon

VN-05Check for cables and pipes before you drillCables and pipes can run almost anywhere in a wall, and bathrooms often hide extra pipework behind tiles. Run a detector over every mark, but treat it as a warning, not a guarantee — detectors miss cables that are deep, in metal conduit, behind metal-backed board, or outside the usual safe zones, and a metal stud frame can confuse a cheap detector further. Confirm your stopcock is off and turns freely before you drill, and if there's any doubt at all, isolate the electrics at the consumer unit and make sure the water is off before cutting into anything that could carry water.

VN-06Drill and fit your fixingsDrill each marked hole to the size and depth worked out in VN-03 — for masonry behind dot-and-dab, drill through the board and dab gap first with a wider bit, then swap to the masonry bit for the final 40–50mm into solid material. If you're fixing a plywood pattress instead, screw it firmly to the studs first, then mark and drill your fixing holes through the pattress. Blow or vacuum the dust out of every hole so the plug or anchor grips properly, and fit each fixing loosely for now.

1 each · Dust brush/vacuum

Buy:ScrewfixB&QToolstationAmazon

VN-07Lift and fix the vanity unit to the wallWith a helper, lift the unit onto the fixings and check it's sitting level with a spirit level before tightening anything fully. Tighten masonry anchors to a firm resistance and pattress screws until snug — don't overtighten, or you risk stripping the fixing. Push gently on the front edge to check the unit doesn't rock or pull away from the wall.

VN-08Connect the water supply and wasteConnect the tap tails to the isolators or supply pipes using flexible tap connectors, hand-tight then a quarter turn with a spanner — don't overtighten or you'll crack the fitting. Fit the waste trap to the basin outlet and join it to the existing waste pipe with a push-fit or compression joint, checking the alignment first. Wrap PTFE tape clockwise round any threaded joints for a better seal.

2 each · Flexible tap connectors

Buy:ScrewfixB&QToolstationAmazon

1 each · Basin waste trap kit

Buy:ScrewfixB&QToolstationAmazon

1 roll · PTFE tape

Buy:ScrewfixB&QToolstationAmazon

VN-09Turn the water back on and check for leaksTurn the water back on slowly at the stopcock or isolators and run both taps for a minute. Check every joint underneath — tap tails, waste trap and any unions — for drips using a dry tissue to spot small leaks. Tighten gently if needed and check again after 10 minutes.

VN-10Seal the joints and tidy upRun a bead of bathroom sealant along the join between the unit and the wall, and around the basin edge, to stop water getting behind it. Smooth it with a wet finger or sealant tool for a neat finish. Wipe down the unit, remove the dust sheets, and dispose of any old fixings or packaging responsibly.

1 tube · Anti-mould bathroom sealant

Buy:ScrewfixB&QToolstationAmazon

1 each · Sealant smoothing tool

Buy:ScrewfixB&QToolstationAmazon

Some links may earn us a small commission at no extra cost to you.

Save this as a project

Back to all guides