How to Prevent Mold on Windowsills

Josh Arnold

It's easier to prevent mold from forming on windowsills than trying to remove it. Mold can form on both painted and stained windowsills, either from condensation buildup or an airflow issue within your home.

Prevent mold growth to keep wood windowsills looking their best.

Once you address these issues, you can prevent both green and black molds -- which each have the potential to damage the wood windowsill if left on it over time -- from appearing. Mold growth inside your home may also be hazardous to your health, so it's important to address the issue before it starts.

Why Mold Forms on Windowsills

Mold can form on wood windowsills when condensation, or moisture, builds up around the window. The moisture may come from humid outside air that's allowed in, plumbing leaks and even cooking steam. In the bathroom, moisture from daily showers can also cause mold to form if there isn't adequate airflow. Condensation can also appear during the winter months when the warm, heated indoor air meets the cold window glass. The problem begins when the condensation is allowed to sit on the sill over a period of time -- mold needs moisture to grow. Green mold is fairly common in households and is easier to remove than black mold -- which is less common but can be hazardous to your family's health and needs to be removed by a professional. Mold can also form on exterior window stools -- the outside sills -- from high outdoor humidity levels.

Mold Rots Windowsills

It's important to prevent mold growth on your windowsills because it can damage the wood if allowed to accumulate over time. Mold can cause both painted and stained wood windowsills to rot, which will damage the structure. It's best to prevent the mold from ever forming, but if it does appear, you can stop it from ruining the wood if you remove it right away.

Preventing Mold with Proper Airflow

Inadequate airflow is one major reason why mold grows on windowsills. If the humid air inside your home is stagnant, moisture builds up on the sills. One way to maintain good airflow is to set your thermostat at 70 degrees with the fan on "auto" on warm days. Keep your doors and windows closed while the air conditioner is on, because the combination of warm and cool air can also cause moisture buildup on the sills. It's also a good idea to install an exhaust fan in the bathroom, to help remove moisture and keep the air flowing during hot showers. An exhaust fan above your kitchen stove eliminates excess humidity from boiling water and other liquids. Use a dehumidifier in rooms or areas that tend to stay damp, such as the basement.

Regularly Remove Condensation to Prevent Mold

Another easy way to prevent mold growth is by regularly removing any condensation from your windowsills. You can do this by wiping the moist sills down with a clean, dry cloth or sponge. If you suspect any mildew or mold growth beginning, wipe the wood down with a mixture of 50 percent bleach and 50 percent water to stop the process. This mixture, however, won't kill mold that has penetrated into the wood -- another reason why you need to stop mold growth immediately.