Your Guide To Mold On Windows And Window Sills

This post may contain affiliate links. Read our full disclosure.

Are you looking for information about mold on windows and mold on window sills? You’ve come to the right place! Today we are talking about window mold including the causes, removal, prevention, and it’s dangers.

When people refer to mold on windows they are usually referring to mold on window sills. Window panes themselves do not provide the right environment for mold to grow. Glass itself is not conducive to mold growth but what is ON the glass might be. Windows panes can collect dust, oils, grease, and other organic materials that can grow mold under the right conditions.

Mold on window panes is usually easy to see with the naked eye and also very easy to remove. More on that in a short bit.

Mold on window sills can sometimes be hard to detect and it’s causes can vary. A lot of the time, the mold is easy to see, but other times it can be the same color as your window frame. The same goes for mold in the window track. It is sometimes very obvious but other times it blends in with other dust and debris that collect in the window tract.

Mold growing around the top of a window. Second image shows mold growing on the window sill

What Causes Mold On Windows and Mold On Window Sills?

Humidity and condensation are the main culprits for mold on window sills.  This is especially true when there are temperature differences between the indoor and outdoor air during cold weather months. The warm, indoor air can condense around cold, often drafty windows which creates moisture.  If the moisture is not wiped up or dried out then window sills and window casings/trim become damp and allow mold to grow. 

Windows that are not sealed well or have cracked or missing caulking are also prone to mold growth. Again, this is because moisture is allowed in through these cracks. In addition, dust, which carries mold spores, can come in through those areas and set up shop.

If you keep your shades drawn this can also create a hospitable environment for mold growth around windows. When temperatures outside are below those inside, wall and window surfaces are warmed by natural air convection currents which cause room air to drop past the surface of the window as the air in contact with the window cools, which causes it to become denser and drop, pulling in less dense, warmer air from further out in the room to replace it.  Window blinds and draperies, when closed, interfere with this convection current and allow the air between the blind and the window to become significantly cooler than it otherwise would. This means more condensation on the window. Sunlight can also help warm up and dry any moisture around windows.

In the case of aluminum frames, indoor dust that is rich in organic matter can accumulate in the joint where the glass meets the frame. This joint can trap the condensation that exists near the windows, ensuring optimum conditions for the growth of mold.

In the case of wood frames, the moisture trapped near the joints of the wood and glass is enough to encourage the growth of mold as the wood is the organic substrate that provides the food for the mold.

Cracked, torn, and damaged seals, weatherstripping, and flashing around windows can allow wind blown moisture to penetrate your house.

Weep holes that are blocked with debris allow for water buildup in the frame. 

Improperly installed windows are also a top reason for moisture intrusion and mold both around the window sill but also into the wall cavity.

Window frames that rely on seals and sealants at internal and exposed joints will eventually leak water as these joints fail over time.

Window mold on a wooden window frame. Also condensation on the window
Mold growth on an old single pane window and wood window frame

Is Window Mold or Window Sill Mold Dangerous?

Just like any other type of mold, mold growth on or around a window can be very dangerous. Not only can it trigger health issue or flare allergies but it can also be a sign of a larger mold problem.

Water accumulation in walls that is not caused by a leak or flood is usually caused by problems with the windows. Mold growth on a window sill may indicate an improperly installed window, a problem with the window flashing, or a defective window. This not only allows moisture accumulation on the window sill but also inside the wall. So if you have mold on window sills anywhere in your home, you may consider doing some further mold testing or moisture inspections to ensure that the problem has not gone into your walls.

How To Remove Mold On Windows

Removing mold on windows is very easy and relatively safe. It is very important that you use disposable cleaning cloths. I recommend paper towels or newspaper for this job.

Step 1. Spray the entire window (frame included) with EC3 Mold Spray. Allow it to dry for 5 minutes.

Step 2. Spray the entire window (frame included) with EC3 Mold Spray a second time. This time, slowly wipe the window pane off with paper towels or newspaper. You want to wipe in a downward motion. I typically place a paper towel in the window track and over the bottom window frame when I do this. This way, if a mold spore gets loose the paper towel can catch it. Repeat this process until all of the mold has been removed from with window pane.

Step 3. Since the EC3 may leave a film on the window, spray your window pane with undiluted vinegar and wipe clean.

How To Remove Mold On Window Sills

This really depends on the type of window sill you have. A wood window sill is much more complicated than an aluminum or vinyl window sill. In addition, if water has penetrated your wall, you will need to actually remove your windows to address the moisture and mold issues inside the wall. This likely requires professional mold remediation and new windows and frames.

How To Remove Mold On Aluminum and Vinyl Window Sills

You must wear protective gear to prevent mold spores from touching your skin or getting into your lungs. You will need:

Step 1. Tape this plastic over doorways and air vents to prevent airborne mold spores from spreading to other parts of your home.

Step 2. Open the window you are removing the mold from. This provides fresh air, easy access to all parts of the window, and helps dry the area.

Step 3. Spray the window and frame with EC3 Mold Solution. You want to saturate the area basically. This will render the mold spores in active and reduce the spread of mold spores as you work.

Step 4. Dip a wad of paper towels in the EC3 Mold Solution. Wipe off all of the mold you can see.

Step 5. Don’t assume that you have removed all the mold at this point. You need to grab an old toothbrush, soft bristle brush, or bottle brush. Spray the entire window and window sill with EC3 Mold Solution again. Using your brush of choice, scrub all areas of the window track, sill, etc… You really want to get into every nook and cranny with your brush. If you see mold on your brush, rinse it in clean water, wipe the area dry, respray with EC3, and keep repeating until no mold appears on your brush.

Step 6. Wet an old rag with water and wipe the entire window area and window sill. Allow it to dry while you clean up your debris.

Step 7. After the window sill is dry, give it one last light spray with EC3. This will take care of any loose mold spores that might have hidden from you.

How To Remove Mold On Wood Window Sills

The problem with mold on wood window sills is that you don’t know how deep the mold has penetrated. It may have rooted all the way through the window sill and possibly into the drywall below. My best advice is to replace all wood window sills but I understand that this is not an affordable option for everyone.

My method for removing mold from wood window sills does not guarantee complete removal of mold seeing that there is no way of knowing how deep it runs but it is the most thorough method. Please be sure you follow each of these steps closely.

You wear protective gear to keep prevent mold spores from touching your skin or getting into your lungs. You will need:

Step 1. Tape this plastic over doorways and air vents to prevent airborne mold spores from spreading to other parts of your home.

Step 2. Vacuum the area to remove any loose mold spores (along with any other accumulated dirt and debris). Ideally you will use a HEPA vacuum.

Step 3. Saturate the window sill with EC3 Mold Spray.

Step 4. Using a soft bristled brush, gently scrub the surface of the window sill to remove any visible mold.

Step 5. Once you have removed all of the visible mold, spray the window sill with EC3 Mold Solution again. Wipe the window sill with a disposable cloth and inspect it for any remaining mold. If you don’t see any mold, proceed to the next step. If there is mold on the wood window sill, repeat steps 4-5.

Step 6. Sand the wood. This is a step most people want to skip once they have removed any visible mold but THIS IS THE MOST IMPORTANT STEP! Remember – if there is mold you can see there is also mold you cannot see. Therefore, you MUST attack the mold that has rooted beyond the top layer of the wood window sill. This means you need to Sand The Wood!

Sanding is the only way to reach the mold deep within the wood. You can use sandpaper or a more robust power sander. Either way, you want to work the sandpaper slowly around the affected area. You ideally want to remove 2-3 layers from the window sill. If there is visible mold you must continue to sand until it has been completely removed OR until you realize you are just going to need new windows.

Step 7. After sanding, HEPA vacuum away all debris.

Step 8. Spray the window sill with Superstratum Mold and Mildew Protectant to prevent future mold growth. Allow to dry for 48 hours.

Step 9. Refinish the wood with a mold resistant paint or stain.

*When cleaning any window sill, always be sure to carefully bag up your used cleaning towels, brushes, etc… and tightly seal it closed. Double bag it then place it in the outside garbage can. Also be sure to empty the HEPA vacuum bag into the outside trash and spray the vacuum with EC3 Mold Solution after you have completed the window mold removal project.

Mold around window and under window coverings
Mold can easily grow around a window due to blinds, shades, and window coverings

How To Prevent Mold On Windows and Window Sills

  1. Properly install high-quality, insulated windows. Opt for frames that rely on welding of joints rather than sealants as they have a longer moisture resistant service life. Caulking of the nail flanges is critical to the prevention of moisture instrusion.
  2. Fill any gaps/drafts around the windows with mold resistant caulk.
  3. Keep the shades open as much as possible to let in sunlight and to allow airflow to get to the windows.
  4. If the windows continue to get condensation, dry them off immediately.
  5. Keep window panes, window tracks, and window sills dust free by cleaning them weekly.
  6. Make sure window weep holes are dust and debris free.
  7. Keep indoor humidity low by using a dehumidifier if necessary.
  8. Mold spore counts are highest in fall and spores are released at night and very early in the morning. Before and after rain storms are also peak times for mold spores. As much as possible, keep your windows closed at these times.
  9. Maintain good airflow in your home.
  10. Keep the thermostat above 70 degrees .
  11. Seal wood window sills with mold resistant paint or mold resistant stains. Beeswax has been known to help prevent mold on window sills as well. I like this Beeswax sealant as it also contains orange oil.
  12. Spray Superstratum Mold and Mildew Protectant on wood window sills to prevent mold for up to 25 years! You can read my post on Superstratum for more information on how this product works but it is nothing short of amazing! Better yet, it is non-toxic.

In Conclusion

Window and window sills are high risk areas not only for growth themselves but for leaks and moisture penetration in general. This is why it is important to practice good mold prevention on a regular basis as well as doing things like properly winterizing your home and routinely fogging to keep airborne mold spores at bay.

In this post I refer to EC3 products. They are one of the only three mold and mycotoxin removal products that I personally use and recommend. Please read my article outlining what makes EC3 superior when it comes to killing mold and mycotoxins. It has been independently lab tested and proven to be 99% effective when used properly. I encourage you to purchase EC3 products directly through Micro Balance. If you prefer to shop on Amazon, Micro Balance has a presence there as well.

Mold growing around a window with an aluminum frame

Leave a Reply

Your email address will not be published. Required fields are marked *


  1. Rick Davis says:

    It’s great to learn that you should get an inspection on your walls if you see mold developing on your window seals. My wife and I are wanting to prevent mold from growing on our windows and we were wondering what we can do to prepare our house better. I’ll be sure to tell her that we should get an inspection of our walls and windows before mold starts to grow.

  2. I currently see mold growing on the sealing strips/caulk of our storm windows and in between the storms and main window. My husband wants to take out the storms and screens and clean it all ourselves. This entails removing the storms via the main window. Removing them by bringing them inside the house and carrying them outside to clean them. I have mast cell activation and we have 5 kids. This terrifies me because I fear spores and mycotoxins being released into our home with each storm window removed and carried out. Any tips/ ideas to make this process more effective and less risky? I read your post on what to wear and what to clean with.

    1. Hi Sarah! Would there be a way to wrap each storm and screen in 6mil plastic as they are pulled out? This way you reduce the change of spores falling through the house as they are carried through.