Cut out rotten timber, treat and fill with epoxy resin, then sand, prime and paint to match the frame.
RWF-01Check the weather and set upPick a dry day with no rain forecast for at least 24 hours, since epoxy filler and paint need to stay dry to cure. Lay a dust sheet under the window and put on gloves and a dust mask before you start. Gather your tools so you are not stopping halfway through.
RWF-02Strip back the old paint and puttyScrape off flaking paint and any old putty around the rotten patch with a scraper, going a bit wider than the damage looks. This lets you see the full extent of the rot before you commit to cutting anything out. Sweep or brush away loose flakes as you go.
RWF-03Cut out all the rotten woodUse your chisel to dig out the soft, rotten timber until you reach solid wood on every side. Test as you go by pressing a bradawl or screwdriver point into the timber — sound wood resists, rotten wood crumbles or lets the point sink in easily. Don't leave any soft patches behind, or the repair will fail early.
RWF-04Treat the exposed timber with wood hardenerBrush liquid wood hardener onto all the bare, cut-back timber. It soaks in and stiffens the fibres so the filler has something solid to grip. Leave it to cure for the time stated on the tin, usually a few hours, before moving on.
RWF-05Mix and pack in the epoxy repair fillerMix the two-part epoxy wood filler exactly to the pack ratio until the colour is even. Press it firmly into the cavity with a filler knife, building it up in layers if the hole is deep, and slightly overfill so you have material to sand back later. Leave it to cure fully — check the pack for time, as it varies with temperature.
RWF-06Shape and sand the repair flushOnce fully cured, use a chisel to trim off the bulk of the excess filler, following the original profile of the frame. Finish with sandpaper, working from a coarser grit down to a finer one, until the repair is smooth and flush with the surrounding wood.
RWF-07Prime the bare wood and fillerApply exterior wood primer over the filler and any bare timber you exposed. This seals the repair against moisture and gives the topcoat something to grip. Let it dry fully before the next step.
RWF-08Fill any remaining pinholesCheck the primed surface for small pinholes or dips and fill these with a fine exterior filler. Let it dry, then sand lightly with a fine grit sandpaper so the whole area feels smooth to the touch.
RWF-09Paint to match the frameMask off the glass and surrounding surfaces with tape. Apply two coats of exterior paint or gloss in the same colour as the rest of the frame, letting each coat dry fully before the next.
RWF-10Clean up and dispose of waste safelyClean your chisel, filler knife and brushes straight away before anything dries on them. Let any rags used with epoxy or hardener cure fully before binning them, as some can generate heat as they dry. Remove the masking tape and dust sheet once the paint is fully dry.
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