Black mold dies with bleach, vinegar, or hydrogen peroxide — but the method depends on the surface and the size of the affected area

Black mold (usually Stachybotrys chartarum, though other dark molds are often called black mold) is killed by common household cleaners, but the surface matters. Non-porous surfaces like tile and glass respond to bleach or vinegar. Porous materials like drywall, wood, and carpet absorb moisture and mold deep into the material, so surface cleaning alone won't stop regrowth — you'll need to remove and replace the material itself. The real work is stopping the moisture that let the mold grow in the first place.

Key Takeaways

  • Bleach kills black mold on non-porous surfaces like tile and glass, but does not penetrate porous materials like drywall or wood.
  • Porous materials with mold deeper than the surface layer need to be removed and replaced, not just cleaned.
  • The moisture source — a leak, poor ventilation, or condensation — must be fixed or the mold will return within weeks.
  • Mold larger than about 10 square feet or mold in HVAC ducts should be handled by a professional mold remediation company.
  • Wear gloves, eye protection, and a respirator rated N95 or better when cleaning mold, and ventilate the room during and after.

Killing mold on tile, glass, and other non-porous surfaces

Non-porous surfaces don't absorb water, so mold stays on the surface where cleaners can reach it. Mix one part household bleach (5% sodium hypochlorite) with ten parts water in a spray bottle. Spray the affected area, let it sit for 10 minutes, then scrub with a stiff brush and rinse thoroughly with clean water. Bleach is fast and reliable, but it produces fumes and can damage or discolor some materials, so test it on a hidden spot first.

If you prefer to avoid bleach fumes, white vinegar (5% acetic acid) works on non-porous surfaces too, though it takes longer. Spray undiluted vinegar directly on the mold, wait one hour, scrub, and rinse. Hydrogen peroxide (3% solution, the kind sold in drugstores) also kills mold on non-porous surfaces — spray it on, wait 10 minutes, scrub, and rinse. None of these methods will harm tile grout or glass, but always ventilate the room and wear gloves and eye protection.

Why cleaning alone fails on drywall, wood, and carpet

Porous materials are the problem. Mold doesn't just sit on the surface — it sends roots (called hyphae) deep into the material. When you spray bleach on moldy drywall, you kill the visible mold, but the roots stay alive in the paper and gypsum underneath. Within two to four weeks, the mold grows back because the moisture is still there and the roots never died.

The only way to truly remove mold from drywall is to cut out the affected section and replace it. For wood framing, studs, or joists, the same rule applies — if the mold has been there long enough to visibly colonize the wood, the wood is compromised and should be replaced. Carpet and carpet padding cannot be salvaged once mold takes hold; they must be removed and the subfloor dried and treated. This is not a limitation of the cleaner — it is a limitation of the material.

Finding and stopping the moisture source

Mold cannot grow without moisture. If you kill the mold but don't stop the water, you are cleaning the same spot every few weeks. Before you clean anything, find the source: a roof leak, a plumbing leak, condensation from poor ventilation, or water intrusion from outside walls or basements.

Check for active leaks by looking for water stains, soft spots, or discoloration spreading from a single point. If the mold is on a ceiling, the leak is above it — check the attic or the room directly above. If it's on a wall, check both sides of the wall and the space behind it. If it's in a bathroom or kitchen, check under sinks and around pipes. Once you find the leak, repair it or improve ventilation (run the bathroom exhaust fan during and 20 minutes after showers; use a dehumidifier in damp basements). Without this step, the mold returns.

When to hire a professional mold remediation company

Mold larger than about 10 square feet (roughly a 3-foot by 3-foot area) should be handled by a professional. Large infestations release more spores into the air during cleaning, and professionals have equipment like HEPA vacuums and negative air machines to contain the spores. They also have the experience to find hidden mold in walls, ducts, and crawl spaces.

Mold in HVAC ducts, attics, or crawl spaces is also a job for professionals — these spaces are hard to access safely, and disturbing mold in a duct system can spread spores throughout the house. If you have health conditions like asthma or a weakened immune system, let a professional handle any mold removal, even small areas. A mold remediation company will assess the extent of the problem, remove affected materials, treat the area, and help you identify the moisture source.

Safety gear and ventilation during cleaning

Wear nitrile gloves (latex can degrade in bleach), eye protection, and a respirator rated N95 or better. An N95 mask is the minimum; if you are sensitive to mold or the area is heavily colonized, use a P100 respirator, which filters more particles. Open windows and doors to ventilate the room, and if possible, use a box fan in a window to push air out. Do not use a household fan to circulate air — it can spread mold spores around the room.

Never mix bleach with ammonia or other cleaners — the combination produces toxic chlorine gas. If you are cleaning a large area or if you feel dizzy, nauseous, or short of breath, leave the room when ready and get fresh air. These are signs of mold spore exposure or chemical fume inhalation.

Preventing black mold from returning

After you've cleaned or removed the mold and fixed the moisture source, keep the area dry. Run exhaust fans in bathrooms and kitchens. Use a dehumidifier in basements or other damp spaces — aim for indoor humidity below 50%. Insulate cold water pipes to prevent condensation. Check gutters and downspouts to make sure water drains away from the foundation. Seal cracks in basement walls and around windows.

If mold returns in the same spot within a few months, the moisture source was not fully fixed. Go back and look for a leak you missed, or consider whether the room needs better ventilation or a larger dehumidifier. Recurring mold in the same location is a sign that the underlying problem — not the mold itself — needs attention.

Frequently Asked Questions

Is black mold toxic?

Black mold produces compounds called mycotoxins, but the health risk from household mold is debated. People with asthma, allergies, or weakened immune systems are more likely to have symptoms like coughing or wheezing. If you have health concerns, consult your doctor and consider hiring a professional to handle the removal.

Can I paint over black mold?

No. Paint does not kill mold and will not stop it from growing underneath. The mold will continue to spread, and the paint will eventually peel. You must remove the mold and the moisture source before painting.

What if the mold is in my air conditioning unit?

Mold in an AC unit or ductwork should be handled by an HVAC professional or mold remediation company. Cleaning it yourself can spread spores throughout your home. Have the system inspected and cleaned by someone licensed to work on HVAC systems.

How long does it take for black mold to grow?

Mold can begin to grow within 24 to 48 hours of exposure to moisture. Visible colonies usually appear within one to two weeks if conditions remain wet and warm. This is why fixing leaks quickly is important — the sooner you dry the area, the less time mold has to establish itself.

Do I need to test the mold to know if it's dangerous?

Mold testing is expensive and usually not necessary. Any mold in your home should be removed, regardless of the species. If you have health symptoms you think are related to mold, talk to your doctor rather than ordering a test.