How to Repair a Water-Damaged Window Sill

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 labor-intensive process of repairing rotting wood with epoxy primer and wood filler.

Things You'll 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

Water Marks

Step 1

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

Step 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.

Step 3

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

Severe Damage, Including Rotting Wood

Step 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.

Step 2

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

Step 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.

Step 4

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

References & Resources