How to Kill Mold on a Window Sill

Mold is a fungi that grows in damp or humid areas. It can grows on just about anything, including your window sill. A window sill can be particularly vulnerable because of condensation on the window. Water can also leak in through the window frame.

With a few guidelines and materials, you can kill mold on a window sill.


  1. Clean off the window sill. Remove any dirt, cracked paint or other debris. Scrape off any visible mold with a spatula. Use a non-metallic spatula to avoid scratching the wood.

  2. Create a solution to kill the mold. Mix 1/2 cup bleach and 1/2 cup laundry detergent with one gallon water.

  3. Test the solution on a small portion of the window sill to see if it has any adverse effects. If the wood changes color, use a solution of water and detergent only.

  4. Scrub the solution into the mold with a sponge. Keep scrubbing until the mold is gone.

  5. Allow the window sill to dry completely. Open the window if it is a dry, non-humid day. Scrub and let the window sill dry again if mold persists.

Stubborn Mold Treatment

  1. Apply a commercial mold-killing product available at most hardware or home improvement stores. Scrub the window sill with a wood-cleaning product.

  2. Sand the window sill to get at the mold's roots.

  3. Apply a wood finisher or repaint the window sill after sanding. Make sure all the mold is gone before painting. Mold will grow under paint.

  4. Tip

    Attack the mold as early as possible. Avoid letting water stand on the wood for too long. Water can damage the wood.


    Be careful working around mold. Wear old clothes, rubber gloves, eye goggles and a painter's mask. Mold can be toxic.