We get asked to clean mouldy carpet a few times every wet season. We say no, and this post explains why.
Mould in carpet is almost never a surface problem. It grows where moisture sits longest, which is underneath: in the underlay, against the backing, on the subfloor. What you see on top, if you see anything at all, is usually the last stage of something that’s been going on for a while. And Health Canada’s guidance on it is blunt: carpets and underpads that are mouldy should be cut out and thrown away.
So this isn’t a guide to scrubbing mould out of carpet. It’s a guide to finding it, knowing when it’s serious, getting the right person in, and keeping it from coming back.
How to Tell If There’s Mould in Your Carpet
The smell: A musty, earthy smell that’s stronger close to the floor is the most common first sign, and often the only one. It tends to get worse on damp days and when the heat comes on.
Spots or discolouration: Green, black, grey or white patches, sometimes fuzzy, sometimes just a stain that wasn’t there before. On the top of the carpet this usually means the problem underneath is well established.
A carpet that never quite feels dry: If one area stays cool and slightly damp to the touch days after anything was spilled on it, moisture is coming from somewhere.
Where it is: Mould in carpet tends to show up in the same places. Basements, especially carpet laid straight onto concrete. Along exterior walls. Under windows that run with condensation all winter. Beside bathrooms. Under large furniture that stops air moving. Beneath potted plants. Anywhere there’s been a leak.
People in the house feeling worse indoors: Health Canada notes that people living with damp and mould are more likely to have eye, nose and throat irritation, coughing, wheezing and worsening asthma. If symptoms ease when you’re out of the house, that’s worth paying attention to.
Checking Under the Carpet
If you suspect mould, look underneath before you decide anything.
Wear gloves and a mask. Go to a corner of the room near where the smell or damp is strongest, and lift the carpet off its tack strip with pliers. Fold back enough to see the underlay and the floor.
What you’re looking for: dark staining or growth on the underlay or the back of the carpet, damp underlay, water marks on the subfloor, and a much stronger smell once it’s lifted. A small amount of dust and fibre is normal. Spotty, coloured growth isn’t.
If you find it, put the carpet back down gently rather than pulling more up. Lifting mouldy carpet disturbs spores, and that’s a job for someone with containment equipment.
How Big Is the Problem?
Health Canada sorts mould into three sizes, and the size is what decides whether you can handle it yourself.
Carpet is the catch. A patch you can see on top of carpet is rarely the full size of what’s underneath, so it’s easy to think a problem is small when it isn’t. Mould that comes back after it’s been cleaned up is another reason Health Canada gives for calling a professional.
We Don’t Remove Mould
To be clear about this: AAA Miracle doesn’t do mould removal or remediation, and we don’t clean carpet that has mould growing in it.
That’s not us being cautious for the sake of it. Hot water extraction puts water into a carpet. On a healthy carpet that’s how it gets clean, and properly extracted it dries in hours. On a carpet with mould in the underlay, adding moisture is the last thing it needs, and no amount of cleaning removes growth from the underlay and subfloor where it’s actually living. You’d be paying for a clean that makes the carpet look better for a week while the problem underneath carries on.
What you need is a mould remediation specialist. They assess how far the growth has spread, set up containment so spores don’t travel through the house, remove the affected carpet, underlay and anything else that’s contaminated, and treat the subfloor. Many will also find the moisture source, which matters more than anything else, because mould removed without fixing the cause comes back.
If you rent, tell your landlord in writing as soon as you find it, with photos.
Why Cleaners and Sprays Don’t Solve It
There are plenty of products sold as mold carpet cleaners, and it’s easy to see the appeal. The problem is where the mould is.
A spray reaches the top of the pile. The growth is usually in the underlay and on the back of the carpet, which a spray never gets to. Even mould that’s been killed isn’t gone: dead mould can still cause allergic reactions, so the material has to come out, not just be treated.
Two things in particular to avoid:
- Bleach: Health Canada says plainly not to use bleach to clean up mould. On carpet it also strips the colour.
- Steam cleaning or shampooing it yourself: It adds moisture to exactly the place that’s already too damp, and a home machine can’t pull much of it back out.
Vacuuming mouldy carpet with an ordinary vacuum isn’t a good idea either. It can push spores into the air and through the rest of the house.
What About Area Rugs?
A rug can sometimes be rescued where wall to wall carpet can’t, because you can see both sides of it and it isn’t sitting on underlay. But Health Canada notes that porous materials like fabrics often can’t be properly cleaned once mould has grown in them, and a rug with growth on the back or a smell that won’t go is in that category. Valuable or sentimental rugs are worth showing to a rug specialist before you throw them out. Everyday rugs usually aren’t worth the risk.
How to Stop It Coming Back
Mould needs moisture, and in a Vancouver home from October to April there’s a lot of it about. Health Canada says mould can start growing in an area with excess moisture within 48 hours, so most prevention comes down to not letting carpet stay wet.
- Keep indoor humidity between 30% and 50%: That’s Health Canada’s recommended range. A basic hygrometer costs very little and tells you where you are. If it’s over 50%, a dehumidifier, especially in the basement, makes the biggest difference.
- Deal with water the same day: A spill, a leak from a plant pot, wet boots left on the carpet. Get it up and get air moving across it.
- Watch the window walls: Condensation running off cold windows soaks the carpet edge below them all winter. Wiping the sills each morning and leaving blinds open a little so air reaches the glass both help.
- Don’t let carpet stay wet after cleaning: Whoever cleans it, the carpet should be dry within hours, not days. If you clean it yourself with a rental machine, use less water than you think and make more drying passes. If it’s still damp the next day, something went wrong.
- Get the carpet off concrete if you can: Basement carpet laid straight on concrete is the most common place we see mould problems start. If you’re replacing it anyway, ask about a moisture barrier or a different floor.
- Fix leaks properly: Any carpet that got wet more than once in the same spot has a source that hasn’t been dealt with.
A professionally cleaned carpet should dry in a few hours, which is part of why we use truck-mounted extraction for home carpet cleaning: far more of the water comes back out than a home machine manages. But cleaning is maintenance for healthy carpet. It isn’t a mould treatment, and we won’t sell it as one.
Quick Answers
Can carpet cleaning remove mould? No. Cleaning reaches the carpet pile, but mould in carpet usually grows in the underlay and on the backing. Health Canada advises that mouldy carpet and underpad be cut out and discarded.
Does AAA Miracle do mould removal? No. We don’t remove mould and we don’t clean mouldy carpet. For that you need a mould remediation specialist, who can assess the spread, contain it and remove the affected materials safely.
Can mould grow under carpet without being visible on top? Yes, and it usually starts there. A musty smell or a patch that stays damp is often the only sign until the problem is well established.
How fast does mould grow in wet carpet? Health Canada says mould can begin to grow within 48 hours in an area with excess moisture, so wet carpet needs to be dried quickly.
Is mouldy carpet dangerous? Health Canada has concluded that indoor mould may pose a health hazard, with effects such as eye, nose and throat irritation, coughing, wheezing and worse asthma. Infants, children, seniors and people with breathing conditions are at higher risk.
Should I use bleach on mouldy carpet? No. Health Canada advises against using bleach to clean up mould, and on carpet it will also remove the colour.