How to Clean and Prevent Mold on Your Window sill

Mold on a window sill is more than an annoying occurrence – it can spread and pose health hazards if not promptly cleaned.

Mold can grow in almost any moist environment. Since windows are at high risk for condensation and leaks, they provide prime growing conditions. The good news is that cleaning small patches of mold is easy, and you probably have the supplies to do it.

What Causes Mold on a Window Sill?

If you’re dealing with mold around your window sill, you’re not alone- here’s how to clean it and prevent it from returning.

What Causes Mold on a Window Sill?

The main cause of mold on a window sill is water build-up caused by condensation, a leak, or high humidity. 

Condensation occurs when warm air meets cool air. For example, if it’s scorching hot outside and you have the ac running full blast, your window will come into contact with warm and cool air, potentially causing condensation. The most common place for condensation is between the window panes, but it can also affect the window sill.

Another common cause of mold is window leaks. A window left to leak can develop mold, mildew, and rot.

High humidity can also cause water to form on a window sill, leading to mold. High humidity is most common during hot summer days.

What Does Mold on a Window Sill Look Like?

Mold on a window sill looks like patches of green, brown, or black dots. It’s often concentrated in one spot and looks like blotches. Sometimes mold will be yellow, white, or pink.

How to Clean Mold on Your Window Sill

Cleaning mold from your window sill is easy. According to the EPA, as long as the moldy area is less than 10 square feet, you can clean it yourself

To get started, you’ll need white distilled vinegar and paper towels. The acidity of the vinegar will kill the mold spores and help prevent them from returning.

To clean your window sill, follow these steps:

  • Fill a spray bottle with white distilled vinegar
  • Spray the mold
  • Allow the vinegar to sit for an hour
  • Wipe away the mold with a paper towel and throw it in the trash
  • Dry the surface with a fresh paper towel

If the mold remains, use a scrub brush or a mixture of baking soda and water to scrub it off the window. Then, lightly spray the area with vinegar and allow it to dry.

How to Prevent Mold on Your Window Sill

You’ll need to deal with moisture issues to prevent mold from returning. Here’s what you can do:

  • Fix leaks – If your windows are leaky, you’ll need to fix them. If the leak is coming between the frame and glass, you can seal the area by adding a bead of clear silicone caulk. If the glass is cracked, you’ll need to replace it.
  • Wipe away condensation -If your windows are prone to condensation, wipe it away every time you see a build-up. Without moisture, mold spores won’t grow.
  • Keep humidity levels in check – During the summer, your humidity levels should be about 50 to 60%. In the winter, they should be lower, about 30-40%. You can run a dehumidifier to lower humidity levels if needed. 
  • Replace old windows – If your windows are more than 20 years old and condensation or leaks are a frequent problem, it might be time for replacements. A replacement window with double or triple pane glass and a Low-E coating will eliminate condensation and leaks.

Frequently Asked Questions (FAQ)FAQ

Will bleach kill mold on a window sill?

Bleach doesn’t kill all mold spores. In fact, cleaning a moldy window sill with bleach can leave behind spores, giving them a chance to regrow. White distilled or cleaning vinegar is the better choice for eliminating the mold at its source.

Can a window ac unit cause mold on a window sill?

A window ac unit can cause mold on a window sill. The most likely culprit is condensation from the ac unit leaking into the window. 

Can I kill mold on the window sill with rubbing alcohol?

Rubbing alcohol can kill some types of mold but is not as effective as vinegar. White distilled and cleaning vinegar are the top two products for safe mold removal

Final Thoughts

Mold on a window sill is a common household problem. Since windows are prone to moisture issues, they give mold the optimal environment to grow. If you notice mold on your window sill, clean it with white distilled vinegar and monitor the humidity levels in your home.

Keep mold from reappearing by keeping your windows dry. If your windows are old and leak, now may be a good time to replace them.