How to Repair Dry Rotted Window Sills

Written by susan defeo Google
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How to Repair Dry Rotted Window Sills
Repairing a dry rotted window sill is a moderately easy job. (window image by Marjan Veljanoski from

Dry rot is a wood decay caused by fungi which lives off lumber with an elevated moisture content. It is often referred to as brown rot. Wood window sills are especially prone to dry rot, which causes a breakdown of the wood, resulting in holes. There are epoxy treatments which kill the rot and restore structural integrity. With a few common tools, some epoxy consolidant and some time, even the uninitiated homeowner can repair dry rotted window sills like a pro.

Skill level:
Moderately Easy

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Things you need

  • Hammer
  • Chisel
  • Electric drill
  • 3/16 inch drill bit
  • Epoxy consolidant
  • Disposable brush
  • Rubber gloves
  • Exterior wood filler
  • Putty knife
  • Block of wood
  • Sandpaper
  • Primer
  • Paint
  • Paintbrush

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  1. 1

    Stick a screwdriver into the rotted area of the window sill. If it penetrates more than 2 inches, a brand new replacement sill is in order. If it hits sound wood at less than 2 inches, the sill can be repaired.

    How to Repair Dry Rotted Window Sills
    Take the screwdriver test. (screwdriver image by Federico Romano from
  2. 2

    Use a hammer and chisel to chip away rotted wood from the window sill. If the wood is wet, let it dry. Once it is completely dry, make sure to cover the area from further wet weather conditions until you are ready to work on the sill.

    How to Repair Dry Rotted Window Sills
    Hammer and chisel away rotted wood. (hammer and chisel image by AGphotographer from
  3. 3

    Hold the electric drill at an angle and drill a series of 3/16 inch holes, resembling a honeycomb pattern, into the rotted area.

    How to Repair Dry Rotted Window Sills
    Hold the drill at an angle. (drill image by Albert Lozano from
  4. 4

    Saturate the rotted section of wood with epoxy consolidant, found at your local hardware store. Use a disposable brush or a squeegee bottle to apply the epoxy, wearing rubber gloves to protect your hands. Allow the epoxy to dry thoroughly.

    How to Repair Dry Rotted Window Sills
    Wear rubber gloves to protect skin. (medical gloves image by sasha from
  5. 5

    Use a putty knife to apply the exterior wood filler to the rotted area. Cover the repaired area with plastic and run a block of wood over it to level the wood filler. Allow it to dry for 48 hours, ensuring that the repaired section stays covered from the elements. When the area has thoroughly dried, sand, wipe clean and prime. Allow the primer coat to dry for 48 hours before painting.

    How to Repair Dry Rotted Window Sills
    (old house window image by Kathy Burns from

Tips and warnings

  • To repair large areas, you can save on the cost of wood filler by filling the hole with small slivers of scrap wood. Slather the cavity with wood filler, press in the wood slivers then cover with more wood filler.
  • Wood repair fillers have a tendency to harden rapidly, in less than 15 minutes. It is wise to work with only a little filler at a time to avoid problems resulting from the filler setting too quickly. Powdered fillers are a good alternative. They do not dry up in the can as do many premixed fillers, and you can mix up the exact amount you need, when you need it.

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