How to Kill Mold on a Window Sill

1. Wear Protection

   Put on waterproof gloves, a mask, and safety glasses.

2. Dry Off the Window Sill

   If the window sill is wet, dry it off by wiping it down with a clean, absorbent cotton or microfiber towel.

   Tip

   Don't try to remove any mold at this time. Just remove the water and anything else that might act as a barrier to the vinegar working on the mold.

3. Spray the Vinegar

   Pour about 1 cup of undiluted white vinegar into the spray bottle. Mist the mold area, thoroughly saturating it. Let the vinegar solution sit for about an hour. Do not rinse it off or touch it in the meantime.

4. Scrub the Mold

   Scrub the vinegar solution with the nylon brush. You'll need to rub vigorously since mold can become embedded in paint.

5. Let Dry, Then Assess

   Let the window sill dry out, then assess it. Every spot of mold must be gone for the window sill to be fully clear of mold. Even one remaining spot of mold will be enough for the mold to quickly reactivate. If the mold isn't gone, then switch to bleach.

6. Prepare the Bleach Solution

   Clean out the spray bottle. Clean off the brush, too. Add 1 cup of bleach and 1 cup of cool water. Replace the sprayer to close up the bottle, then slosh the bottle gently to mix.

7. Spray the Bleach

   Mist the bleach solution on the window sill to saturate the mold.

8. Scrub the Mold

   Similar to earlier steps, vigorously scrub the mold on the window sill with the nylon brush. Work the bleach solution into the mold.

9. Wash Off the Bleach Solution

   Thoroughly wash off the window sill to remove the mold and the bleach solution.
   

   Tip

   If the paint is discolored from the mold, after cleaning you can apply a coat of mold resistant primer and repaint the affected area.

How to Prevent and Control Mold on a Window Sill

• Eliminate window moisture: In cold months, condensation beads up on windows when it's warm and humid inside but cold outside. In warm months, it's the opposite. Use a dehumidifier and encourage airflow to reduce condensation.
• Keep the window sill clean: Dust, dirt, and hair that collect on the window sill provide food for the mold to grow. Regularly wiping down the window sill goes a long way toward preventing mold growth.
• Use mold-resistant paint: Aside from having a tight molecular structure that discourages mold growth, mold- and mildew-resistant paint has fungicides that help kill mold spores.
• Choose glossy paint: Paints that have higher sheens are better at resisting mold because they are less porous and less absorbent. Paint the window sill with semi-gloss or glossy paint.

When to Call a Professional

Call a mold remediation company if the mold on the window sill is part of a larger problem that extends up or down the wall, inside the wall cavity, or on the ceiling. When selling a house that has mold problems, the buyer sometimes requests a paid invoice from a mold remediation company as a condition of sale.