Fill the gap around a pipe coming through a wall — HomeGraft

Seal and neaten the gap where a pipe passes through a wall, matching the method to your wall type.

PG-01Work out what kind of wall you've gotTap the wall near the pipe. Solid brick or block sounds solid all over. A stud wall sounds hollow between the studs and solid where you hit one. Dot-and-dab plasterboard sounds hollow in the middle of each panel but solid where the adhesive dabs are, roughly every 300-400mm. Lath and plaster feels slightly springy and sounds hollow with a faint give. If it's a stud wall, find out if the studs are timber or metal: run a magnet or stud detector along the wall to pick up screw heads, and if you drill a small pilot hole, timber gives fine wood dust while metal gives grey metallic swarf. Metal studs are common in flats, new builds and anywhere refitted since the 1990s.

1 each · Magnetic stud finder

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1 each · Electronic stud/cable detector (optional, more reliable)

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PG-02Check whether this is a fire-separating wall or floorThink about where the pipe goes. If it passes between flats, into a communal stairwell or hallway, or through a floor between storeys, this wall or floor is likely there to stop fire spreading. If you're not sure, treat it as one to be safe.

RULES

KNOW THE RULES

Building Regulations Part B requires proper fire-stopping where a service like a pipe passes through a wall or floor that separates fire compartments (for example between flats, or through a floor between storeys). Ordinary expanding foam and standard sealant are not fire-rated. Use a fire-rated sealant or collar in these locations, and get advice if in doubt.

PG-03Turn off water and check for cables before you drill anythingFind your stopcock, usually under the kitchen sink, and check it turns freely before you start. If you hit a pipe by accident you need to be able to shut the water off straight away. Cables and pipes can run almost anywhere, so use a detector, but still assume something is there until you've proved otherwise. If there's any doubt at all, isolate the relevant circuit at the consumer unit before drilling near it.

PG-04Clear and clean the gap around the pipeVacuum out old dust, loose masonry crumbs, and any bits of old insulation from the gap. Brush away debris with a small brush and wipe the pipe itself clean of grease or dust with a cloth so sealant and foam stick properly.

1 each · Small brush

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1 each · Cloth rag

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PG-05Fill a small gap (up to about 5mm) with sealantFor a narrow gap all the way round the pipe, run a bead of sanitary silicone sealant into it with a sealant gun. Smooth it with a wet finger for a neat finish. This works the same on brick, block, plasterboard on any stud type, dot-and-dab and lath and plaster.

1 tube · Sanitary silicone sealant

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1 each · Sealant gun

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PG-06Fill a bigger gap (5-40mm) with expanding foamFor a wider gap, use a low-expansion gap-filling foam so it doesn't bulge or push the pipe out of line. Fill roughly two-thirds full and let it expand into the rest. If step PG-02 flagged this as a fire-separating wall or floor, use a fire-rated foam or sealant instead of standard foam.

RULES

1 can · Low-expansion gap-filling foam

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1 can · Fire-rated foam or sealant (if fire-separating wall/floor)

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KNOW THE RULES

If this is a fire-separating wall or floor (see PG-02), Building Regulations Part B means you must use a fire-rated product here, not ordinary expanding foam.

PG-07Fit a pipe collar or escutcheon plate for a neat, sealed finishA collar plate covers the gap and hides raw foam or sealant. On solid brick or block, mark the fixing holes, drill 6mm holes to about 30mm deep, and use plastic wall plugs with 30-40mm screws. On plasterboard over timber studs, find the centre of the nearest stud and drive a 35mm wood screw straight in, no plug needed. On plasterboard over metal studs, never use a wood screw or plastic plug, as it will strip straight through the thin steel; use a self-drilling metal-stud screw or a small snap-toggle fixing instead. On dot-and-dab plasterboard, use a long fixing, around 50-75mm, that passes through the board and air gap to bite into the masonry behind. On lath and plaster, try to catch a lath if you can find one, or use a spring toggle through the plaster, as a screw straight into old plaster alone will crack it. A pipe collar is light, so these simple fixings are enough on their own.

1 each · Pipe collar or escutcheon plate

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2 each · Plastic wall plugs (masonry)

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2 each · Wood screws 35mm (timber stud)

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2 each · Self-drilling metal-stud screws

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2 each · Long dot-and-dab fixings 60mm

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2 each · Spring toggle fixings (lath and plaster)

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PG-08Trim and smooth once curedLeave foam to cure fully, usually a few hours, then trim off the excess with a sharp knife so it sits flush behind the collar plate. Wipe away any smears of sealant with a damp cloth before it skins over.

1 each · Sharp utility knife

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PG-09Turn services back on and tidy upTurn the water back on at the stopcock and check for leaks around the pipe. If you isolated a circuit, switch it back on at the consumer unit. Vacuum up dust and offcuts, and wash sealant off tools before it cures on them.

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