How to Repair a Water-Damaged Window Sill

Written by steve sloane
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How to Repair a Water-Damaged Window Sill
Windowsills can become water damaged if not adequately protected. (sprouting on the windowsill image by Rebecca Capell from

Over time, if a windowsill is not correctly shielded from the natural elements, or if a wet mug is simply set down without a coaster, the sill will deteriorate or rot. A water-damaged window sill can, however, be brought back to its best with a minimum of knowledge or know-how. Restoring a sill ranges from the application of toothpaste and baking soda for water stains to the more labour-intensive process of repairing rotting wood with epoxy primer and wood filler.

Skill level:

Things you need

  • Baking soda
  • Toothpaste
  • Cup
  • Rag
  • Furniture polish
  • Utility knife
  • Small flathead screwdriver
  • Medium and fine sandpaper
  • Epoxy primer
  • Brush
  • Wood epoxy filler
  • Putty knife
  • Primer and paint

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  1. 1

    Mix together in a cup a 50/50 solution of baking soda and toothpaste.

  2. 2

    Rub the mixture gently over the water mark with a rag. Wait a few minutes before rubbing in more of the solution. Do this as many times as needed until the water mark disappears.

  3. 3

    Remove all solution, wait for the area to thoroughly dry, and apply furniture polish.

  1. 1

    Scrape off all paint and damaged wood from the area--use a utility knife and small flathead screwdriver. Thoroughly sand the area as well as the edges of any holes. Remove all dust and wood particles.

  2. 2

    Apply a thin layer of wood epoxy primer to the damaged area with a brush. Wait 10 minutes for it to dry.

  3. 3

    Stir the wood epoxy filler and apply it to the damaged area, using a putty knife. Wait for it to dry and sand the area with medium and fine sandpaper until smooth to the touch.

  4. 4

    Prime and paint the sill to seal it from any future weather/water damage.

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