How to Fix a Rotted Window Ledge

A window ledge or sill is often affected by moisture, causing it to degenerate quickly if it is not carefully painted and sealed as necessary. Once the damage is done and the window ledge has begun to rot, the rotted areas should be removed. Then if the entire window ledge is sealed, you will not have to replace the entire window ledge.

This project assumes that the exterior window ledges are painted. This finish will conceal the window ledge repair. If your window ledge is not painted, you may have to replace the entire ledge for a uniform, clean look.

Step 1: Remove any window screen or storm window. Open the window to protect the window from accidental damage.

Step 2: Remove the rotted areas of the window ledge with a chisel and hammer. While you don't want to remove too much of the ledge, don't be afraid to remove all of the rotted areas on the sill until you hit solid wood.

Step 3: Clean the ledge with a soft bristled brush to remove any debris or dirt. If there are stains, they must be removed and the ledge should dry completely before continuing.

Step 4: Paint the entire window sill with a penetrating epoxy sealant. Allow the sealant to cure before continuing: waiting two hours is standard but check the manufacturer's recommendations.

Step 5: Rebuild the chipped away and rotted areas of the window sill with epoxy filler and a putty knife. Add enough epoxy filler so the patched areas are slightly higher than the surrounding sill to allow for shrinkage. Wait for the epoxy filler to cure completely before continuing.

Step 6: Sand down the patched areas until they are level with the surrounding window ledge.

Step 7: Apply a coat of epoxy based primer over the entire window sill. Wait until the first coat is completely dry, then apply a second coat.

Step 8: Apply a coat of epoxy based paint to match the window sill with the other surrounding sills. Apply another coat if necessary, making sure to allow for drying time between coats.