Black spots along window sills, in sliding door tracks and on the rubber seals are something we see in Florida homes every week. Most of the time it’s a condensation problem you can manage. Sometimes it’s a sign the window is letting rain inside the wall.
Why Windows Get Moldy in Florida
- Condensation: cold, air-conditioned glass meets humid air and “sweats,” leaving water on the sill
- Dust and dirt in the tracks: give mold something to feed on
- Clogged weep holes: the small drain openings in window and sliding door frames get blocked, so rainwater sits in the track
- Failed seals or caulking: let wind-driven rain into the frame and wall
- Heavy curtains and blinds: trap moisture against the glass
How to Clean Mold Off Window Sills and Tracks
- Wear gloves and a mask, and open the window if you can.
- Vacuum loose dirt from the track, ideally with a HEPA vacuum.
- Spray with soapy water, 3% hydrogen peroxide or white vinegar and let it sit a few minutes.
- Scrub with an old toothbrush, especially in corners and along rubber seals.
- Wipe clean and dry completely.
- Clear the weep holes with a pipe cleaner or thin wire so water can drain.
Never mix bleach with vinegar or ammonia. See bleach vs. vinegar vs. hydrogen peroxide for which cleaner to use.
How to Prevent It
- Wipe off condensation in the morning if your windows sweat
- Keep indoor humidity under about 60% (see do humidifiers cause mold?)
- Open blinds and curtains during the day so air reaches the glass
- Vacuum tracks and clear weep holes a few times a year, and before hurricane season
- Replace cracked caulk around the outside of the frame
Signs Water Is Getting Into the Wall
- Stains, bubbling paint or soft drywall below or beside the window
- Swollen baseboards or damp carpet under a window or sliding door
- Mold on the wall itself, not just the sill
- Problems that get worse after storms
That points to a leak in the window or surrounding wall. See how to remove mold from walls and how to find hidden mold.
Free Visual Inspection in South Florida
An infrared (thermal) camera can show wet areas around windows that you can’t see. FL Cleanup offers a free visual inspection with moisture readings and an infrared camera, and handles licensed mold remediation across South Florida. We answer 24/7, and hablamos español. Call 877-224-2532 or request a free visual inspection online.
About the author: James Rice-Peña is the owner of FL Cleanup and a Florida-licensed Mold Assessor (MRSA4035) and Mold Remediator (MRSR4158). He has worked in property restoration in South Florida since 2012, and FL Cleanup has earned 200+ five-star Google reviews.
