Replacing a damaged wooden windowsill involves carpentry work because it requires removing an integral part of the frame, which is difficult to do. But you can repair the sill more easily by rebuilding the damaged sill and then shaping and sanding it to conform with its original appearance.
We’ve used two products: a two-part wood filler and hardener from Minwax and a wood filler and stabilizer from Bondo. Both are available at hardware stores and home centers. The filler is designed to fill holes and gouges in the wood, and the hardener and stabilizer are formulated to strengthen and reinforce the decayed or rotting wood. When the repair area is dry, you sand and smooth the surface so it can be finished with a primer and paint to match the existing finish.
