Black mould removal depends on the size of the affected area and what surface it is growing on

Black mould can be cleaned off hard surfaces like tile, glass, and painted walls using household cleaners and a stiff brush. For small patches — less than a square metre — you can handle the job yourself with bleach, vinegar, or a commercial mould killer. Larger areas, mould inside walls or insulation, or mould in homes where someone has a weakened immune system should be assessed by a professional before you start, because disturbing it can spread spores through the air.

The key difference between removing mould and preventing it from coming back is addressing the moisture that allowed it to grow in the first place. Black mould thrives in damp, poorly ventilated spaces. If you clean it but leave the source of moisture untouched, it will return within weeks or months.

Key Takeaways

  • Small patches of black mould on hard surfaces can be cleaned with bleach, vinegar, or commercial mould killer and a stiff brush.
  • Wear gloves, eye protection, and a mask rated N95 or higher when cleaning mould to avoid inhaling spores.
  • After cleaning, identify and fix the moisture source — poor ventilation, leaks, or condensation — or the mould will return.
  • Patches larger than one square metre, mould in walls or insulation, or mould in homes with vulnerable people should be handled by a professional.
  • Prevent future growth by keeping humidity below 50 percent, fixing leaks promptly, and ensuring bathrooms and kitchens are well ventilated.

What you need to clean black mould safely

Wear nitrile gloves (latex can break down in bleach), eye protection, and a mask rated N95 or higher. The mask is not optional — mould spores are small enough to lodge in your lungs, and black mould produces toxins that can irritate airways even in people without respiratory conditions. If you have asthma, emphysema, or a suppressed immune system, do not do this work yourself.

You will also need a stiff-bristled brush (not soft), a spray bottle, and one of these cleaning agents: household bleach (5 percent sodium hypochlorite), white vinegar, or a commercial mould killer. Bleach works fastest but produces fumes and can damage some surfaces. Vinegar is slower but safer for painted walls and fabrics. Do not mix bleach with ammonia or other cleaners — the combination produces toxic gas.

Open windows and doors to create airflow before you start. If the room has no windows, use a fan to push air out through a doorway. Do not use a portable air purifier in the room while you are cleaning — it can spread spores around instead of containing them.

Steps to remove black mould from hard surfaces

Step 1: Spray the affected area. Mix one part bleach to ten parts water in a spray bottle, or use vinegar straight from the bottle. Spray the mould generously and let it sit for 10 to 15 minutes. This gives the cleaner time to kill the spores before you disturb them.

Step 2: Scrub with a stiff brush. Use firm pressure to scrub away the mould. You are removing both the visible growth and the root structure (called hyphae) that anchors it to the surface. Scrub until the surface is clean and the mould is gone, not just lighter in colour.

Step 3: Rinse and dry. Wipe the area with a clean, damp cloth to remove the cleaner and dead mould. Then dry it completely with a towel or let it air dry with the window open. Moisture left behind can allow new mould to start growing within days.

Step 4: Dispose of materials. Throw the cloth or sponge you used in a sealed bag. Do not reuse it for other cleaning tasks.

Mould on porous surfaces like drywall and fabric

Porous materials — drywall, insulation, carpet, and upholstered furniture — are harder to clean because the mould grows into the material itself, not just on the surface. If the mould is only on the surface of drywall and the patch is small, you can try cleaning it with vinegar and a soft brush, but understand that the spores may have already penetrated the material.

If the mould has been there for more than a few weeks, or if it covers an area larger than 30 centimetres across, the safest approach is to remove and replace the affected section. Drywall is inexpensive and straightforward to cut out and patch. Carpet and padding underneath often need to be replaced entirely because moisture trapped underneath allows mould to spread unseen.

Do not paint over mould or use sealant to trap it. The mould will continue to grow underneath, and you will have a much bigger problem later.

Finding and fixing the moisture source

Black mould grows where moisture is present. Common sources are leaking pipes, roof leaks, poor bathroom ventilation, condensation on windows, and water seeping through basement walls. If you do not fix the source, the mould will return to the same spot within a few weeks.

Check for visible leaks first: look under sinks, around toilet bases, and along the seams of your roof from the attic. If you find a leak, repair it or call a plumber. For condensation problems — mist on windows, damp corners, or mould around bathroom tiles — run the bathroom exhaust fan during and for 20 minutes after showers, keep kitchen windows open while cooking, and use a dehumidifier if indoor humidity stays above 50 percent.

In basements, mould often signals water seeping through walls or a high water table. This usually requires professional assessment, as the fix might be anything from better grading around the foundation to installing a sump pump or interior drainage system.

When to call a professional

Do not attempt to remove mould yourself if the affected area is larger than one square metre, if the mould is inside walls or insulation, if it is in the HVAC system, or if anyone in the home has asthma, a respiratory condition, or a weakened immune system. A professional mould remediation company has equipment to contain spores, remove affected materials safely, and identify hidden moisture sources.

You should also get a professional assessment if you have had a flood, a major roof leak, or water damage that was not dried within 48 hours. Mould can be growing in places you cannot see — inside walls, under flooring, or in the attic — and a visual inspection alone will not find it.

Ask any professional you hire for a written scope of work that includes what will be removed, what will be cleaned, and what moisture source will be addressed. Some companies will clean the mould but leave the leak unfixed, which means you will call them again in a few months.

Preventing black mould from returning

Keep indoor humidity between 30 and 50 percent. You can measure it with an inexpensive hygrometer from a hardware store. If humidity is consistently above 50 percent, use a dehumidifier or improve ventilation by opening windows, running exhaust fans, or installing additional vents.

Fix leaks as soon as you notice them — a small drip under a sink or a damp patch on a ceiling will grow into a mould problem within weeks. Dry any water damage within 48 hours: use fans, open windows, and remove wet materials if necessary. In bathrooms, squeegee shower walls and the tub after use to reduce standing water, and wipe down mirrors and windows to remove condensation.

may support your bathroom and kitchen exhaust fans vent outside the house, not into the attic or crawl space. A fan that vents into the attic straightforward moves moisture there, where it will cause mould in insulation and wood framing.

Frequently Asked Questions

Is black mould dangerous?

Black mould produces toxins called mycotoxins that can irritate airways, trigger asthma attacks, and cause respiratory symptoms in people with existing lung conditions. Healthy people may experience coughing, wheezing, or sore throat from exposure. People with weakened immune systems, severe asthma, or chronic lung disease face greater risk and should not be in a home with active mould growth.

Can I use bleach on all surfaces?

Bleach works well on tile, glass, and non-porous hard surfaces, but it can damage or discolour painted walls, wood, and fabrics. Test it on a hidden area first. For painted surfaces and fabrics, use white vinegar instead — it is slower but safer and will not bleach colours.

How long does it take for mould to come back after cleaning?

If you clean the mould but leave the moisture source in place, it can return within two to four weeks. If you fix the moisture source and keep humidity low, mould should not return to that spot. If it does, the moisture problem was not fully resolved.

Do I need to use a HEPA filter while cleaning?

A HEPA filter in a portable air purifier will not help while you are actively cleaning — it may even spread spores around the room. Open windows and use fans to push air out instead. After you finish and leave the room, a HEPA filter can help remove spores from the air over the next few hours.

What if the mould smell remains after cleaning?

A lingering musty smell usually means moisture is still present or mould is growing in a place you cannot see — inside walls, under flooring, or in the HVAC system. Do not assume the smell will go away on its own. Have a professional inspect for hidden moisture and mould growth.