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Repair a Rotten Wood Windowsill

When wood rot attacks a wooden windowsill, you need to fix this as quickly as possible unless you want to replace the entire window frame. Cutting out and replacing damaged wood is easy if you use a Dremel cutting tool.



If you don't regularly maintain wooden window frames, chances are that sooner or later you will end up with rotten wood where wood rot has gained a foothold. You can repair damage that hasn't affected the structural integrity of a wooden window frame, and here's how...



  • Dremel Multi-Max kit
  • Pencil and ruler
  • Meranti or saligna to replace damaged wood
  • Wood glue, exterior grade
  • Primer, undercoat and paint to match existing finish






Before you start , press your finger into the wood on your windowsill to check which areas feel soft. Where the wood is soft or crumbly, it's rotten. You will need to cut out an area slightly larger than the soft areas, so that you are sure to remove all the rot. Use a pencil and ruler to mark where you need to cut.



Cutting out the damaged section is reasonably simple. Start with a vertical cut to the sides and back of the rotten wood. The easiest way to do this is using a Dremel Multi-Max fitted with the wood and metal flush cut blade MM422.



Each Dremel Multi-Max Kit includes accessories: hook and loop sanding pad with sanding papers, wood and metal flush cut blade and wood and drywall saw blade. This kit also includes 2x 10.8V li-Ion batteries with ECP technology for longer working.



Cut along the bottom front edge of the rotten area with the wood and drywall saw blade MM450 to remove the rotten section. If the piece of wood is too deep to cut out the rotten area in one go, then cut it out in sections. Cut a new piece of hardwood to replace the rotten area and use exterior wood glue to secure in place.



Finally, face fill any gaps with Alcolin QuikWood epoxy putty and sand using the hook and loop sanding pad MM11 and the sanding pad for wood MM70W, starting with P60, then P120 and finishing with P240. To finish prime, undercoat and paint to match the existing frame.