Fix a gap between the bath and the wall

Clean the gap, decide on sealant or a trim strip, then seal or fix it neatly for a lasting, waterproof finish.

AB-01Measure the gap and pick your methodRun a tape measure along the join between bath and wall at several points, as it's rarely even. Gaps up to 5mm just need sealant. Gaps of 5-10mm need a foam backing rod under the sealant. Gaps over 10mm, or ones that open up when the bath is used, need a rigid bath edge trim strip screwed to the wall.

1 each · Tape measure

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AB-02Strip out the old sealant and clean upCut through the old silicone with a sealant remover tool or a sharp filling knife, then peel it away from both the bath edge and the wall. Wipe both surfaces with methylated spirit to remove grease, soap scum and mould, then let them dry fully. Sealant won't stick to a damp or dirty surface.

1 each · Sealant remover tool

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1 bottle · Methylated spirit

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2 each · Clean cloths

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AB-03Fill the bath to settle it before sealingFill the bath about halfway with water and leave it for a few minutes. This drops the bath to the lowest position it will sit at when someone's using it, so the seal doesn't crack the first time it's filled. Seal with the water still in, and drain it after the sealant has cured.

AB-04If fitting a trim strip, work out the wall type behind the tilesSkip this step if you're only sealing. If the gap needs a rigid trim strip, find out what's behind the tiles first. Run a stud detector or magnet up the wall in a line — regular screw heads mean plasterboard on timber or metal studs, no pattern and a dull, solid knock means solid brick or block, and a hollow knock everywhere with a bouncy feel means dot-and-dab or lath and plaster.

1 each · Stud and cable detector

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AB-05Check for cables and pipes before you drillCables and pipes can run almost anywhere behind bathroom tiles, and a detector can miss deep cables, metal conduit or anything behind metal-backed board — so use one, but still drill as if something's there. Find your stopcock, usually under the kitchen sink, and check it turns before you start. If you're at all unsure, isolate the circuit at the consumer unit first, and turn the water off at the stopcock before cutting into anything that could carry water.

AB-06Fix the trim strip with the right fixing for your wallIn solid brick or block, drill a 6mm pilot hole 40mm deep, fit a wall plug, and use a 30mm screw. Into a timber stud, screw a 4x30mm wood screw straight into the centre of the stud, no plug needed. Into a metal stud, use a self-drilling metal-stud screw or hollow-wall toggle rated for it — never a plain wall plug or wood screw, as they strip straight through 0.5mm steel. Through dot-and-dab, use a 60-75mm fixing that reaches past the plasterboard and adhesive dabs into the solid wall behind; through lath and plaster, use a spring or rubber toggle fixing, as a screw into the lath alone will pull straight out.

6 each · Wood screws 4x30mm

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6 each · Metal-stud self-drilling fixings

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6 each · Wall plugs and screws (masonry)

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6 each · Long frame fixings 75mm (dot-and-dab)

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6 each · Rubber toggle fixings (lath and plaster)

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1 length · Bath edge trim strip

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AB-07Mask both edgesRun a strip of low-tack masking tape along the top edge of the bath and another up the wall, leaving an even 4-5mm gap between them for the sealant bead. Press the tape down firmly so sealant can't creep underneath.

1 roll · Low-tack masking tape

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AB-08Apply the sealantIf using a backing rod for a wider gap, push it in first so the sealant only bonds to the two sides, not the bottom. Load a sanitary-grade silicone sealant into a sealant gun, cut the nozzle at 45°, and run one steady, continuous bead along the gap.

1 each · Sealant gun

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1 tube · Sanitary silicone sealant

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1 length · Foam backing rod

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AB-09Tool the bead smoothDip a finger or a sealant shaping tool in soapy water and run it along the bead in one continuous stroke. This pushes the sealant into the gap and leaves a neat, slightly concave finish.

1 each · Sealant smoothing tool

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AB-10Peel off the tape while it's still wetPull the masking tape away straight away, before the sealant skins over, pulling it back on itself at a 45° angle. This leaves a crisp, straight edge on both sides of the bead.

AB-11Leave it to cureCheck the curing time on the sealant tube, usually around 24 hours, and don't run water or bathe until it's passed. Once cured, drain the bath you filled earlier in step three.

AB-12Tidy upWipe the sealant gun nozzle and put the cap back on any part-used tube. Bin old sealant scrapings and tape, and open a window to clear the smell while the sealant cures.

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