How to Repair a Rotted Window Sill
A window sill directs water away from the window and creates a surface where the bottom sash of the window can seal. Replacing a rotten wood window sill can be a major project since removal of the sill may require removal of the window for access. However, a wood window sill can be repaired without removing the entire sill, making this a one-day job that most homeowners can accomplish with regular carpentry tools. Does this Spark an idea?
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Things You'll Need
- Putty knife
- Pry bar
- Claw hammer
- Reciprocating saw
- Pliers
- Wood chisel
- Measuring tape
- Scrap wood pieces
- Handsaw
- Circular saw
- Exterior grade wood glue
- 8D galvanized finish nails
- Hand plane
- Electric drill
- 1/16-inch drill bit
- 100 grit sandpaper
- Exterior grade caulk
- Primer and paint
Instructions
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Scrape the paint off of the sill on the outside wall to locate any nails with a putty knife. Pull out nails with a pry bar and a claw hammer.
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2
Cut the projecting section of sill flush with the exterior siding with a reciprocating saw. Remove and set aside the cut-off piece of sill. Remove any nails revealed in the remaining sill with a pair of pliers.
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3
Remove any remaining rot in the sill by chipping it out with a wood chisel and hammer. Square off the ends of the cut-out area with the chisel. Use a measuring tape and cut a block of scrap wood to the exact dimensions of the cut-out area with a handsaw or circular saw. Apply exterior grade wood glue to the block and drive it into the hole gently with a hammer. Drive 8D galvanized finish nails through the block and into the sill to hold it while the glue dries.
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4
Use a hand plane to trim the entire length of the cut-off area of sill so the surface is perfectly flush with the exterior siding. Use a measuring tape and transfer the measurements of the cut-off piece of sill to a good piece of scrap lumber. Cut the piece of scrap wood to the length and width needed with a circular saw.
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If the old sill sloped downward to drain off water, duplicate the same angle of slope onto the edge of the new piece by adjusting the base of a circular saw to match the angle. Cut the edge of the new piece with a circular saw.
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6
Drill pilot holes into the sill repair board with an electric drill and a 1/16-inch drill bit. Apply exterior grade wood glue to the mating surface of the repair piece and nail it to the existing sill with 8D galvanized finish nails.
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Allow the glue to dry for 24 hours and sand all surfaces of the repair area with 100 grit sandpaper. Apply exterior caulk around all edges of the new sill. Prime and paint the sill after the caulk as dried.
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Tips & Warnings
When using a reciprocating saw to cut the sill, install the blade with the teeth toward the top of the saw. This will enable you to hold the saw in the upright position while cutting instead of the more awkward upside down position.
