Replacing a rotted or damaged windowsill is pretty simple: Take out the old sill, cut a replacement sill and install it.
Things You'll Need
- Finish Nails
- Measuring Tapes
- Wood Putty
- Pry Bars
- Saber Saws
Take some overall measurements of the windowsill for width, length and thickness.
Remove the sash channel trim and side pieces of casing trim to get access to the sill. Work loose any trim with a small pry bar. Rest the pry bar on a small block of scrap lumber to keep it from marring other trim or walls.
Pull all nails left in the walls or window jamb. Remove nails in the trim with pliers, pulling them through the back of the trim.
Remove the sill piece itself, trying damage it as little as possible. (The easiest method is to use the old sill as a template for the replacement.)
Take the old sill to your local lumberyard or home improvement center. Purchase replacement lumber and 6d or 8d finish nails.
Trace the pattern of the old sill directly on the new lumber - or make careful measurements and transfer those to the new lumber.
Cut out the new sill with a saber saw. Use a fine-toothed (finish cut) blade to make the cuts as smooth as possible. You might have to do some sanding, especially for exposed end grain cuts.
Fit the new sill in place and use a couple of nails to hold it there. Replace the trim you removed with a couple nails for each piece. Once you are satisfied with the fit, nail all pieces securely. Countersink all nails with a nail set.
Fill all nail holes (old and new) with wood putty. Paint or stain to match your decor.
Tips & Warnings
- If you plan to paint the windowsill, you can save a little money by using pine or another inexpensive wood, instead of oak, ash or mahogany.
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