Step 3: Apply the Adhesive

man applying adhesive for installing new windowsill
Ryan Benyi Photo:
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Repair any rotten spots on the old sill with epoxy. Trim the back edge of the new sill as needed so that its lower edge fits tightly against the siding and its back edge fits against the old wood. Drill pilot holes every 16 inches or so through the new sill's front and back edges. Run a bead of waterproof, marine-grade adhesive along the old sill.
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    Tools List

    • circular saw
      Circular saw
    • detail sander
      Multitool
    • drill
      Drill/driver
    • hammer
      Hammer
    • flat prybar
      Pry bar

    Shopping List

    1. 8d stainless-steel ring-shank nails
    for casing

    2. 3½-inch deck screws for sill

    3. Two-part acrylic adhesive (The brand used here is Bond&Fill.)4. Cellular-PVC windowsill (The brand used here is Kleer Lumber, which has the most sill options. AZEK also makes a PVC sill.)