How to Clean Mold From Windows Sill? (Common Causes)

Photo of a windows full of black mold. How to Clean Mold From Windows?

If you’ve got mold on your windows, you won’t want to leave it there. Learn how to clean mold from windows quickly and easily for your health, safety, and comfort!

The most effective way to clean mold from windows is by combining ¼ to ½ cup of bleach with a gallon (3.78 L) of water. You should let the mix sit on your casings for about 15 minutes. This lifts the mold and kills any spores that are left over.

When the area is thoroughly clean from the bleach, you’ll want to coat it in water to remove leftover bleach. Once that’s done, dry it thoroughly to keep more mold from developing in the moisture! There are other treatment options that I’ll also explain below, too, so read on!

Is mold on windows harmful?

There are a lot of different kinds of mold that can grow on windows. Mold Inspect explains that many mold types are hard to distinguish and can harm your health. Before you clean it from your window, consider having some sent away for testing. 

You should assume that mold on windows is harmful. Many will leave mold there for a while and can suffer issues such as eye irritation, shortness of breath, headaches, skin rashes, and even feeling as though they’re sick all the time.

Is black mold On windows Sills normal?

Black mold around windows is just as normal as having any other kind of mold around windows. Mold can grow around windows from the same causes as other kinds of mold. The top causes of mold build-up include moisture and heat, water damage, and improper ventilation. Since windows are areas where moisture and air can get trapped, it’s widespread to have mold (including black mold) sitting around them.

What kills mold permanently?

Obviously, you don’t want to clean up mold more than once. If you’re looking at doing it right, the first choices for cleaning should be:

  • Vinegar
  • Bleach
  • Baking soda
  • Hydrogen peroxide
  • Tea tree oil


The best type of vinegar for mold is going to be white vinegar. You don’t need to dilute white vinegar with anything for mold clean-up. Just spritz some straight vinegar on the mold liberally! You’ll want to let it sit for about an hour.


As I mentioned in the introduction, combine ¼ to ½ cup of bleach with a gallon (3.78 L) of water and spread this mix liberally over the mold. After 15 minutes, wipe it off again! This is a great choice for killing mold and its spores.

Baking soda

You can use straight baking soda on mold, but it’s stronger if you mix it with vinegar — yes, seriously. Mix the two so that it forms a potent paste. Spread that liberally over the area and allow it to dry into a cakey substance. When it’s totally dry, wipe it off!

Hydrogen peroxide

You can use equal parts of hot water and hydrogen peroxide together. If you want extra strength, you can use it straight, too. Leave it on for about 15 minutes, and then wipe it off before moving on.

Tea tree oil

If you have this around the house, use it for mold destruction, too! Use about ten drops of oil to about a cup (236 ml) of water and spritz it on the mold. After about an hour, wipe it up! This tends to smell better than bleach; I have to be honest.

All these are potent enough that, if used correctly, you can rely on them to kill mold and its spores. There are also some commercial products that you can try if you want. Some of the most common ones are:

  • Microban 24-Hour Bathroom and Sanitizing Cleaner
  • CLR Mold & Mildew Clear Stain Remover Spray
  • RMR Brands RMR-141 Disinfectant

There is no “best one ever” out there if you ask me. Personally, I choose to use bleach or other household options. Since there’s always going to be a need for bleach, vinegar, baking soda, etc., it just makes sense to have it around. It’s so helpful at killing mold; why not use it there, too?


If you have nothing else, soap or detergent, and water can work. You’ll need to do multiple cleanings and scrub hard at the mold. 

Materials needed to clean mold from windows

If you’re ready to get started on cleaning mold from your windows, here are some of the essential materials needed to help you get to the bottom of the problem quickly and — most importantly — safely:

  • Your cleaning agent of choice (bleach, vinegar, etc.)
  • Rubber gloves
  • A face mask
  • Safety glasses/goggles
  • A bucket
  • Clean rags
  • Fresh water

It may seem dramatic to wear a face mask of gloves and eye goggles, but cleaning up mold without them can be dangerous. Mold can harm your health, as I mentioned above, so you’ll want to take care of yourself first!

How to clean mold from windows step by step

If you’ve got your supplies ready, this will be your step-by-step guide for getting to the bottom of your mold problem! Here’s what to do:

  • Vacuum or clean the area thoroughly
  • Get the window area damp
  • Spread your cleaner of choice and follow the instructions
  • Wipe the cleaner off
  • Apply a fresh coat of water
  • Dry thoroughly

Vacuum or clean the area thoroughly

This will remove loose debris or other things that get in your way when you start deep cleaning.

Get the window area damp

With a paper towel, moisten the window area around the mold, so it’s thoroughly wet and ready for treatment. Make sure you have your safety gear on before you have any direct contact!

Spread your cleaner of choice and follow the instructions

Choose whatever cleaner you want to use and apply it according to the instructions I mentioned above. The same goes for any of the commercial products that I mentioned earlier! Take your time with this step since it’s an important one.

Wipe the cleaner off

After the right time has passed, depending on your cleanser option, wipe the cleanser off with one of your clean rags. Don’t reuse the rag again. Throw it out. Make sure you use steady pressure to get off as much as possible!

Apply a fresh coat of water

With a clean rag or paper towel, moisten the area to make it damp again. This gets off any leftover residue.

Dry thoroughly

Now the most critical part; dry the area thoroughly with a towel or by opening the window. You’ll want to focus on this step to keep mold from coming back! I’ll talk about this a bit later, too, if you need more tips.

Is bleach or vinegar better for killing mold?

If you compare them head to head, bleach is better at killing mold. However, vinegar is the second-best option, and it’s natural. It depends on what you are most comfortable using!

What do professionals use to kill mold?

Most professionals use a commercial formula that often contains hydrogen peroxide. Chlorine or alcohol-based options are also really popular for those in the business. The professionals use much stronger concentrations than you would use at home, though.

Will opening a window help with mold?

Opening a window is very helpful with mold. The breeze will cause the mold spores to drift out of your home instead of getting trapped and building up on your window sills. You should also always sop up any kind of standing water from condensation.

Do dehumidifiers remove mold?

Humidity can lead to mold growth, so dehumidifiers can help cut down on the amount of mold in your home. If you live in a humid climate or have had issues with mold before, I recommend investing in a good dehumidifier! It will make your windows and home much less hospitable for further growth.

Dehumidifiers help remove mold by making your window sills and home much less comfortable for mold spores. However, an air purifier is going to be what helps remove mold spores from the air, according to Oransi.

How to prevent mold from growing on the windows

Thankfully, there are many ways to help keep mold from growing on windows, preventatively or after removal! Some of your best choices to fight mold would be keeping a steady airflow in your home, changing the filters in your exhaust fans and air conditioners, and relying on dehumidifiers or humidifiers, as you should at different times of the year. I’ve written about how to prevent mold growth on windows if you want more detail on these choices!

Finding mold on your windows is never good, but it’s nice to know that you can easily take care of it. For best results, combine ¼ to ½ cup of bleach with a gallon (3.78 L) of water. Leave it for 15 minutes, which will lift the mold and kills any spores that are left over. Then rinse your area again, and dry it thoroughly.

You can also use natural options such as vinegar, baking soda, hydrogen peroxide, and tea tree oil. Cleaning up mold is crucial to your health and your home’s integrity, so ensure you learn how to do it right!

Do you know someone who is battling mold right now? If so, consider sharing this with them to help them win the fight!

Rosa Peterson

Rose is the writer and creator of Better That Home, a blog about home design and decor. Rose has been designing spaces for over 10 years and writing home design and decor for big publishers. She has been inspired by many other creatives from around the world and loves to share those inspirations with her readers. Read more about Rose here