Once fully cured (usually overnight), sand the repair flush with the original wood. Start with 80-grit to shape, finish with 150–220 grit for a smooth surface.
Wood must be bone-dry before applying repair products. If the sill is damp, use a heat gun on low (carefully to avoid scorching) or let it air-dry for 24–48 hours. repairing a rotted window sill
Mix your epoxy filler or two-part wood repair compound. Overfill the cavity slightly, then sculpt it to match the original sill profile. Use a putty knife or a shaped piece of plastic (like an old loyalty card) to create the slope and edges. Work quickly—epoxy sets in 15–30 minutes. Once fully cured (usually overnight), sand the repair
Brush a penetrating wood hardener onto the exposed solid wood. This strengthens the remaining fibers and helps the filler bond. Let it cure per manufacturer instructions (usually 2–4 hours). If the sill is damp, use a heat
Tape off adjacent glass or siding before filling to avoid messy smears.