What kills mold and how to use it

The most effective mold killers are bleach, vinegar, hydrogen peroxide, and borax. Bleach works fastest on non-porous surfaces like tile and glass but does not penetrate porous materials like drywall or wood. Vinegar and hydrogen peroxide work on both porous and non-porous surfaces but take longer — usually 10 to 24 hours. Borax is slower still but leaves a residue that prevents regrowth for weeks.

For small patches under 10 square feet, spray the surface with your chosen cleaner, let it sit for the time the product specifies, then scrub with a stiff brush and rinse. For bleach, that time is usually 10 minutes. For vinegar or hydrogen peroxide, leave it overnight if possible. Borax requires mixing with water — one cup of borax per gallon — and also works best left overnight.

Do not mix bleach with ammonia, vinegar, or hydrogen peroxide. The chemical reaction creates toxic gas. If you are using bleach, use it alone and rinse thoroughly before switching to another product.

Key Takeaways

  • Bleach kills mold fastest on tile and glass but does not work on drywall or wood; vinegar and hydrogen peroxide work on all surfaces but take 10 to 24 hours.
  • Spray the cleaner, wait the recommended time, scrub with a stiff brush, and rinse completely to remove both the mold and the dead spores.
  • Mold larger than 10 square feet or mold in HVAC systems, insulation, or crawl spaces usually requires professional removal because it spreads through hidden areas.
  • After cleaning, reduce moisture by fixing leaks, running exhaust fans during and 20 minutes after showers, and keeping indoor humidity below 50 percent.
  • Wear gloves, eye protection, and an N95 mask when cleaning mold to avoid breathing spores or getting cleaner in your eyes.

Safety gear you need before you start

Mold spores become airborne when you scrub, so protect yourself. Wear nitrile gloves to keep cleaner and mold off your skin, safety glasses to protect your eyes from splashing, and an N95 mask to avoid breathing spores. If you are sensitive to mold or have asthma, wear a P100 respirator instead — it filters more thoroughly than an N95.

Open windows and doors to create airflow while you work. If the room has no windows, run a box fan in the doorway pointing outward to push contaminated air outside. Do not use your home's central air system while cleaning mold, because it will spread spores through the whole house.

Cleaning mold on different surfaces

Tile and grout: Spray with bleach solution (one part bleach to ten parts water), wait 10 minutes, scrub with an old toothbrush or grout brush, and rinse. For stubborn grout, let the bleach sit for 30 minutes. If mold returns within a week, the grout is too porous and may need professional sealing or replacement.

Drywall and painted walls: Use vinegar or hydrogen peroxide, not bleach — bleach does not penetrate drywall and can damage the paper facing. Spray vinegar, wait overnight, then wipe with a cloth. If the mold is deeper than the surface or covers more than a few square inches, the drywall is likely compromised and should be cut out and replaced.

Wood: Vinegar or hydrogen peroxide work, but mold in wood often means the wood is rotting underneath. If the wood is soft when you press it, or if mold returns within two weeks, the wood should be replaced. Sealing with paint or stain after cleaning helps prevent regrowth.

Fabric and carpet: If mold is on fabric, throw it away — cleaning does not remove mold that has grown into fibers. If mold is on carpet, the carpet and padding underneath are usually too contaminated to save. Cut out the affected section and replace it.

When to call a professional instead

Mold larger than 10 square feet, mold in HVAC ducts, mold in insulation, or mold in crawl spaces and attics should be handled by a professional. These areas are difficult to access, and incomplete removal spreads spores through your home. A professional has equipment to contain the area, remove contaminated materials, and verify that the mold is gone.

Also call a professional if you have mold and you are pregnant, immunocompromised, or have severe asthma. Exposure to large amounts of mold spores can trigger serious reactions in these groups. If you are unsure whether your mold is small enough to handle yourself, take a photo and send it to a local mold removal company — most offer free phone assessments.

Stopping mold from coming back

Mold needs moisture to grow. After you clean, fix the source of the moisture. If mold is in a bathroom, run the exhaust fan during your shower and for 20 minutes after. If there is no exhaust fan, open a window. Wipe down wet surfaces with a dry cloth after bathing.

In kitchens, use the range hood while cooking and wipe up spills when ready. In basements and crawl spaces, use a dehumidifier to keep humidity below 50 percent. Check for leaks in the roof, walls, and plumbing — a small leak that drips for weeks creates the perfect environment for mold to return.

If mold returns in the same spot within a month, the moisture source is still there. Do not just clean it again — find and fix the leak or ventilation problem first.

Cleaning products and their trade-offs

Bleach: Kills mold in 10 minutes on non-porous surfaces. Does not work on porous materials. Toxic fumes if mixed with other cleaners. Requires good ventilation. Cost is low — a gallon costs a few dollars.

Vinegar: Works on all surfaces. Takes 10 to 24 hours. No toxic fumes. Smell fades as it dries. Cost is low. Does not prevent regrowth as well as borax.

Hydrogen peroxide: Works on all surfaces. Takes 10 to 24 hours. No toxic fumes. Slightly better at preventing regrowth than vinegar. Cost is low to moderate. Can bleach some fabrics and paints if left too long.

Borax: Works on all surfaces. Takes 24 hours or more. Leaves a residue that prevents regrowth for weeks. No toxic fumes. Cost is low. Requires mixing and can irritate skin, so wear gloves.

Frequently Asked Questions

Can I use a bleach spray bottle on mold in my shower?

Yes, but dilute it first — mix one part bleach with ten parts water. Spray it on the mold, wait 10 minutes, scrub with a brush, and rinse thoroughly. Bleach works fastest on tile and grout. Do not use bleach on caulk or silicone sealant, because it can degrade the material over time.

What if the mold smell stays after I clean?

The smell usually means spores are still present or the moisture source is still active. Clean again with vinegar or hydrogen peroxide and let it dry completely. Open windows for 24 hours. If the smell returns within a week, there is likely mold in a hidden area — inside walls, under flooring, or in HVAC ducts — and you should have a professional inspect.

Is black mold more dangerous than other mold?

Black mold (Stachybotrys) is not inherently more toxic than other molds, but it grows in very wet areas and often indicates a serious moisture problem. Any mold larger than 10 square feet or mold that returns repeatedly should be evaluated by a professional, regardless of color.

How long does it take for mold to die after I spray it?

Bleach kills mold in 10 minutes. Vinegar and hydrogen peroxide take 10 to 24 hours — the longer you leave them, the more spores they kill. Borax takes 24 hours or more. Do not rinse too early or you will remove the cleaner before it has finished working.

Can I prevent mold by painting over it?

No. Paint seals the surface but does not kill the mold underneath, which continues to grow and eventually breaks through the paint. Always clean and kill the mold first, let the surface dry completely, then paint.