Seal around a window frame outside

Remove old sealant, clean and dry the gap, then run a fresh weatherproof bead around the window frame to stop draughts and damp.

AB-01Choose the right sealant for the substrateCheck what the wall is made of where the frame sits — solid brick, block, render, or a timber or UPVC surround. For brick, block or render, use a weatherproof exterior sealant such as a low-modulus silicone or a hybrid polymer sealant. If you'll paint over the joint later, choose a paintable hybrid sealant rather than pure silicone, which paint won't stick to. Pick a colour close to the frame or wall — white, brown, and clear are the common choices.

1 each · Exterior weatherproof sealant cartridge

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1 each · Skeleton sealant gun

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AB-02Set up safe accessPosition your ladder or stepladder on firm, level ground, using the ladder safety basics you already know. Make sure you can reach the full length of the frame without stretching sideways. Move the ladder along as you work rather than leaning off it.

AB-03Strip out the old sealantLay a dust sheet below the window to catch debris. Use a hook knife or sealant removal tool to cut along both edges of the old bead, then peel it away. Work slowly to avoid scoring the frame or the brickwork, and wear gloves — old sealant can hide mould, grit, or sharp bits of render.

1 each · Hook knife or sealant removal tool

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1 box · Disposable gloves

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1 each · Dust sheet

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AB-04Clean and dry the jointWipe the gap with a cloth dampened in methylated spirit to remove grease, dust, and any leftover sealant residue. If there's mould or algae, wash it first with sugar soap or mild detergent and rinse well. Let the joint dry fully before sealing — new sealant won't stick properly to a damp surface.

1 each · Methylated spirits, 250ml

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1 pack · Lint-free cloths

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AB-05Fill any large gaps with backer rodIf the gap between frame and wall is wider than about 5mm, push a foam backer rod into it before sealing. This stops the sealant sinking in, gives the bead the right shape to flex with the building, and uses less sealant. Skip this step if the gap is narrow and even.

1 each · Foam backer rod, 5m

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AB-06Mask the frame and wallRun a strip of low-tack masking tape along each side of the gap, leaving only the joint exposed. This gives you a crisp, straight line and protects the brickwork or paintwork from smears. Press the tape down firmly so sealant can't creep underneath.

1 roll · Low-tack masking tape

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AB-07Apply the new sealant beadCut the cartridge nozzle at an angle to match the gap width, load it into the gun, and run a steady, continuous bead along the full length of the joint. Keep the gun moving at a constant speed and angle so the bead stays even. Work in short sections on long windows so the sealant doesn't skin over before you tool it.

AB-08Tool the bead and remove the tapeSmooth the bead with a wet finger or a sealant tooling tool, pressing it slightly into the gap on both sides for a good bond. Pull the masking tape away straight away, at a 45° angle, before the sealant skins over. Wipe off any smears immediately with a damp cloth.

AB-09Clean up and let it cureWipe the gun and nozzle clean, and cap any part-used cartridge with a nail or nozzle cap to stop it drying out. Check the curing time on the tube — most exterior sealants need 24-48 hours of dry weather to fully cure, so check the forecast and keep water off the joint until then. Dispose of the old sealant strips and used tape in general waste.

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