Strip out old sealant, clean the gap, then run a fresh weatherproof bead around the door frame to stop draughts and damp.
SD-01Check the weather and prepare the areaPick a dry day with no rain forecast for at least 12 hours, ideally above 5°C - sealant won't cure properly in the cold or wet. Lay a dust sheet under the door to catch debris. Put on gloves before you start scraping.
SD-02Strip out the old sealantUse a stripping knife or flat scraper to cut and peel away all the old, cracked or peeling sealant from the gap between the frame and the wall. Work along both sides of the door and across the top. Pick out any stubborn bits with a sharp blade, taking care not to gouge the wood or the brickwork.
SD-03Clean and dry the gapBrush out all dust, loose mortar and old sealant crumbs with a wire brush. Wipe the gap with a dry cloth. Sealant won't stick to a damp surface, so if it feels damp, leave it a few hours to dry before going any further.
SD-04Bridge any wide gapsIf the gap between the frame and the wall is wider than about 5mm, push a foam backing rod into it before sealing. This stops the sealant sinking into the gap and gives it the right bead shape to move without cracking. Skip this step if the gap is narrow.
SD-05Mask off both sides for a neat lineRun a strip of low-tack masking tape along the wall and along the frame, leaving only the gap exposed. This gives crisp, straight edges once the tape comes off. Press the tape down firmly so sealant can't creep underneath it.
SD-06Choose and load an exterior-grade sealantUse an exterior-grade polyurethane or hybrid sealant, never an interior decorator's acrylic caulk - acrylic will crack and let water in outside. Cut the nozzle at a 45° angle to match the width of the gap, pierce the foil seal inside with a long nail, then load the cartridge into a sealant gun.
SD-07Apply a continuous beadHold the gun at a steady angle and run an even bead along the gap in short sections, keeping the nozzle moving so you don't leave gaps or blobs. Squeeze the trigger with steady pressure rather than in bursts. Work all the way round the frame, including the top.
SD-08Smooth the bead and remove the tapeSmooth the bead with a wet finger or a sealant smoothing tool before it skins over, using a small amount of soapy water to stop it sticking to your finger. Peel off the masking tape straight away, while the sealant is still soft, for a clean edge. Pulling tape off after it's cured will drag the line.
SD-09Clean up and leave it to cureWipe the gun and any smears off the wall and frame before the sealant hardens. Bag up the old sealant scraps and dust sheet rubbish. Check the tube for the curing time - most need 24 hours dry weather before they're fully weatherproof, so keep the door area covered if rain is forecast sooner.
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