Wooden window frames are considered to be very durable, resistant and tough. However, since they are on the outside of a house, atmospheric conditions affect and damage its structure over time. No matter how well the wood is sealed and protected, if it is not properly maintained, some level of damage is likely to occur. Water damage is one of the most common types of wood deterioration, so if you want to repair your window, you may want to know how to properly repair its rotten wooden frame.
Inspect the level of damage to your window frame. Note that if more than 10 per cent of the frame is rotten, it is essential that the whole window is replaced. Otherwise it will present a serious safety hazard.
Remove all the loose wood from the rotten area of your window frame. Make sure to remove every last bit of wood scraps, dirt and dust from the area. Use a screwdriver to hollow out the rotten wood residue with a scooping motion. Be careful not to damage the healthy parts of the wood.
Apply a rich coat of wood preservative on the entire surface of the wooden window. Use a soft paintbrush for this part of the job, to make sure the preservative penetrates through all parts of the wood structure. This is a necessary step since it will prevent the rot to spread over to the healthy parts of the wood.
Fill the missing parts of the frame with wood putty or epoxy. Use a putty knife to apply layers of filler into the hole and make sure that the final product looks exactly like the frame. Make the surface smooth and even with the rest of the frame. Do not miss a spot and avoid air bubbles, in order to create a compact structure.
Leave the frame to dry and harden for 48 hours. This will allow the filler, whether it's wood putty or epoxy, to settle, harden and strongly adhere to the existing part of the wooden frame.
Treat the entire window frame with sandpaper to even out the whole surface. Use tough grit sandpaper first and then move on to a fine grit sandpaper. At this point, your window frame should look homogeneous in terms of texture. The only thing to differ the patched area from the rest of the frame will be its colour.
Apply a light coat of wood stain to the window frame, making sure to cover the whole surface. Allow the layer of stain to dry thoroughly.
Paint the wooden window frame in the colour of your choice. This step is important because it will make the window look entirely homogeneous, thus making the patch blend seamlessly into the frame. Leave the window to dry before applying the second coat of wood paint. Allow the window frame to dry before applying a layer of wood gloss or lacquer.
Be sure to maintain your wooden window regularly to avoid serious water or moist damage.
Wear latex gloves while using wood preservative.