Prep first
Before you start
- Fix the water source first, since mold needs moisture to grow.
- Put on gloves, goggles without vents, and an N-95 respirator before you touch it.
- Brush loose mold off outdoors if you can, so spores don't spread through the house.
- Scrub hard surfaces with detergent and water if you need a quick first pass, then dry them completely.
Mold on glass in windows usually sits where dampness collects on the sills and frames, and the deciding question is whether the growth stayed on the surface. If it has worked into a porous sill, mold can fill the crevices and may not come out completely. Fresh surface growth lifts most easily, while a dark stain that stays after drying can take a longer effort.
Wipe the sill dry after cleaning, since a damp sill is what brings the growth back. If you're trying to remove mold from windowsills that feel soft or spongy, stop, because the mold has likely gone into the wood. For surface growth, a microfiber cloth and a mold and mildew remover are enough, though a dark stain may need several rounds.
Before you start
What glass, windows & mirrors can take
Safe to use1
- Water
Use with care7
- Hot water
- Soaking
- Chlorine bleach
- Solvents (alcohol, spot removers)
- Acids (vinegar, lemon)
- Scrubbing and abrasives
- Heat, once the stain is out
8 items
What you'll need
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- White vinegarThe base of the light mildew wash. Use white only, since colored vinegar can leave a stain. (opens Amazon)
- Washing sodaGoes into the vinegar solution for light mildew. (opens Amazon)
- Warm waterMix the solution in 1 gallon of warm water.
- Soft cloth or nylon brushLifts the mold without scratching the glass. (opens Amazon)
- Nylon or plastic scrub padSafe on glass. Metal pads are not. (opens Amazon)
- Baking sodaGoes into the paste for heavy stains only. (opens Amazon)
- Chlorine bleachOnly for the paste on heavy stains, as the final step. (opens Amazon)
- Gloves, goggles without vents, and an N-95 respiratorKeeps spores out of your eyes, nose and skin. (opens Amazon)
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5 steps
Step by step
Step 1 of 5
Mix the solution and test it
Mix 1/2 cup white vinegar and 1/4 cup washing soda into 1 gallon of warm water. Test it on a hidden spot first, such as an inside corner of the frame, and see whether the paint or glass changes.
Tip. Use white vinegar only; colored vinegar can leave a stain.
Careful. Glass can break from a sudden temperature change, so let a window that's hot from the sun cool before you wet it.
Step 2 of 5
Wash the stain with the solution
Dip a soft cloth or nylon brush in the solution and work it over the glass, sill and frame. Keep the liquid on the surface, and rinse your cloth often so you aren't spreading dirty solution.
Careful. Skip this step on marble, limestone, travertine, granite or cement grout, since vinegar can damage them.
Step 3 of 5
Scrub with a nylon or plastic pad
Scrub the stain with a nylon or plastic pad, working over the whole marked area. Stop when the dark spots lift, and don't press hard enough to scratch the glass.
Careful. Don't use steel wool, scouring pads or sandpaper on glass.
Step 4 of 524 to 48 hours
Rinse and dry the window
Rinse the whole area with clean water until no suds or vinegar smell remain, then wipe it dry. Let it dry fully, since wet areas dried within 24 to 48 hours usually won't grow mold.
Step 5 of 5
Use the bleach paste on heavy stains
Make a paste of baking soda and bleach, then scrub the stain with a small brush. Ventilate the room, rinse thoroughly, and let the glass dry completely afterward.
Tip. Use this only if the stain survived the vinegar wash and rinse.
Careful. Never mix chlorine bleach with vinegar, ammonia or any cleaner that contains ammonia, because toxic fumes could be produced.
If you'd rather buy than mix
Best products for mold on glass, windows & mirrors
Keep a clean microfiber cloth nearby for a final buff so the glass dries without streaks, and check the window frame for any spots you missed.
Amazon Basics Microfiber Cleaning Cloths
e-cloth General Purpose Cloth
How we picked these: each product is made for this type of stain, its maker doesn't warn against using it on glass, windows & mirrors, and its directions fit the steps above.
Finished the steps? How does it look?
Nice work. Let it dry completely and check it again in good light. Here is what done looks like:
How to tell it's really gone →A faint mark usually needs one more round, not a stronger product.
See what to do for what you're seeing →Heavy buildup usually takes more than one round.
Heavy or long-standing buildup →When to call a professional →How to tell it's working
Once the glass is fully dry, it should look clear with no dark speckling, since damp glass can hide what's left. Light mildew should lift after the vinegar wash, and the frame should look lighter after the first pass. If a dark mark is still there when everything is dry, it's time for the bleach paste as the final step.
What changes for yours
Adjust for your glass, windows & mirrors
Around windows and window edges
Window edges often mix materials, so check what you're cleaning before you pick a method. For stone or cement grout, use detergent and water in place of the vinegar wash.
Dry the edge completely afterward. If mold returns in the same spot, the moisture source is still there and needs fixing before more cleaning.
Window frames and painted frames
Painted wood is porous, so mold can sit under the paint, where a wipe on top won't reach it. Work the vinegar solution over the paint with a cloth wrung nearly dry, and keep the liquid on the surface instead of letting it soak in.
Aluminum frames can be washed with the vinegar solution, but keep the baking soda paste off them, since baking soda can damage aluminum. If mold has gone deep into the wood, cleaning may not remove it completely, so replacement may be needed.
Mildew on window sills and frames
Light mildew is handled by the vinegar wash alone. Heavy mildew stains, the dark marks that stay after washing, need the bleach paste as the final step, so check which one you have before you reach for bleach.
Let the sill dry fully between passes, so you can see what's left. Once the marks look lighter, finish with a rinse and let the frame dry before you judge the result.
Heavy or long-standing buildup
An old mold stain on a cracked pane can sit in the crack, not only on the glass, and a surface wash won't reach it. Mold that has worked into crevices can be difficult or impossible to remove completely.
If the mold has dried on, repeat the vinegar wash and scrub again before anything stronger. A commercial mildew stain remover is the next option, used per the container's directions after you've tested it on a hidden spot.
If the pane is cracked, or the stain returns after the remover and drying, replacing the pane is the realistic fix. Any moisture still reaching the window has to be fixed first, or the mold will likely return.
Vinegar, baking soda, peroxide and more
Do home remedies work on mold on glass, windows & mirrors?
Most home fixes you'll find are written for fabric or stone, so only a few apply to a window. The vinegar solution does most of the work here. The bleach paste is for heavy stains only, and the others suit other jobs better.
Works2Skip4
Chemical safety
Never mix these
Some products in this guide react dangerously with each other. Use them one at a time and rinse with water in between.
Chlorine bleach + Vinegar
Vinegar is an acid, and acid mixed with bleach gives off toxic chlorine gas.
Chlorine bleach + Washing Soda
Clorox says not to mix bleach with other household chemicals, and no maker statement allowing bleach with washing soda was found.
Vinegar + Washing Soda
Arm & Hammer's Super Washing Soda safety data sheet lists acids as incompatible materials. Vinegar is an acid.
If they mix by accident: Stop and add nothing else; leave the area for fresh air, open windows and keep children and pets away; call Poison Control at 1-800-222-1222, or 911 if anyone has trouble breathing.
What makes it worse
Mistakes to avoid
Don't paint or caulk over mold.
Paint laid over mold is likely to peel, so clean and dry the surface first. Only then repaint or reseal the frame.
Don't use cleaners with fluorine compounds.
Fluorine damages ceramic, glass and stone, so check the label of any commercial mildew remover before you buy it. If it lists fluorine, choose another product.
Don't make bleach your routine cleaner.
Chlorine bleach isn't a good everyday choice for mold on glass. Keep it for the rare heavy stain that survived the vinegar wash.
Don't run the heating or cooling system if mold is in it.
If you suspect the system is contaminated with mold, it can spread spores through the building. Get it checked before you run it again.
Troubleshooting
If the stain is still there
Pick what you're seeing:
The glass is clean but the rubber seal or caulk is still dark
Scrub the seal with detergent and water, then try the vinegar wash. If the stain stays, the mold has penetrated the material and the seal may need replacing.
A white film is left after cleaning
That is usually residue from the wash. Rinse again with clean water and dry with a lint-free cloth.
The glass looks hazy after the bleach paste
Rinse thoroughly with clean water, since paste residue dries cloudy. Next time, use lighter pressure and a softer brush.
When to call a professional
Call a professional if the mold covers more than about 10 square feet, or if it came from sewage or contaminated water. For larger or hidden jobs, follow the official remediation guidance and get an experienced professional to check the work.
Questions
Black mold on window sills: how do I remove it?
Treat it the same way as any mold on a sill: start with the vinegar wash, rinse, and dry it completely. Only if a dark stain survives should you use the bleach paste, with the room ventilated and gloves on.
How do you clean mold off window sills?
Mix 1/2 cup white vinegar and 1/4 cup washing soda into 1 gallon of warm water, wash the sill, and rinse it thoroughly. Let it dry fully, and only use the baking soda and bleach paste if a dark stain is still there.
Is bleach safe on window frames?
Yes, but only for heavy stains that the vinegar wash didn't lift, and only after everything has been rinsed clean. Check the frame material first, because the baking soda paste isn't right for every frame.
Will mold come back on my windowsill?
It can, if the moisture that fed it is still there. Mold needs water or moisture to grow, so fix the source first and dry the area within 24 to 48 hours.
Why does the stain stay after cleaning?
Old mold can sink into cracks and crevices, where a surface wash can't reach it. Repeat the wash, then consider a commercial remover, and replace a cracked pane if the stain comes back.
What cleaner works best for mold on windows?
Start with the vinegar solution, which handles light mildew on glass and frames. For what's left, a commercial mildew stain remover made for the surface works, used per the container's directions.
Mold on other materials
Other stains on glass, windows & mirrors
Start from the bigger picture
How we know this
Every method, amount and warning here comes from university extension services, industry bodies and product makers. We read them, check every step for unsafe combinations and changed amounts, and write it up so you can follow it.