Mould under the mats: what happens between the mat and the concrete
The mat is a waterproof blanket laid on a floor. Whatever gets underneath no longer evaporates. That is the definition of a mould environment.
By Mat Maintenance Agency · Published September 5, 2026
Mould under gym mats comes from water seeping into the seams or rising from the floor, trapped between the foam and the concrete with no light or air. The manufacturer Jukado warns that the subfloor can mould or slowly rot because the tatami surface stops water from evaporating. Signs: a cellar smell, black or green stains under the tiles, vinyl delaminating. Solution: dry out the cause, disassemble, treat, replace what is affected.
How water gets under the mat
Once under the mat, the water no longer comes out: the surface is waterproof by design.
- Washing with a soaked mop, water running into the seams
- Water extractor or auto-scrubber on foam tiles
- Basement concrete floor, moisture rising
- Seepage through a wall, a door, an old water leak
- Summer condensation on cold concrete, under a mat laid directly on the floor
What it does
The foam absorbs and swells, the vinyl delaminates from the foam and the tile weakens, says the manufacturer’s guide. The floor moulds then rots if it is wood, or blackens if it is concrete. Health Canada notes that mould growth usually results from a moisture problem, and that people exposed are more likely to suffer eye, nose and throat irritation, coughing, wheezing and worsening asthma. A gym that smells of cellar is not a gym where people train well.
How to see it before it is too late
The three-tile test, every week: lift, look at the underside and the floor, smell. Damp to the touch, stains, cellar smell: act. Once a season, a wider check by taking up a row along the outside walls, where moisture arrives first.
What works
First the cause: you do not treat mould under a mat without fixing the water supply (washing routine, floor, seepage, dehumidifying the room). Then the mat: full disassembly, vacuuming, cleaning and disinfecting the floor, dry steam on both faces of the tiles, registered disinfectant, forced drying until dry to the touch, reassembly. A tile whose foam is affected deep down cannot be recovered: it is replaced, and the numbered plan puts the others back in place.
Preventing it
- Barely damp mop, never standing water
- No extractor or auto-scrubber on the tiles
- Dehumidifier in a basement or a storage room
- Rolls and tiles never stored damp
- Deep clean at a fixed interval, with a look at the floor every time
What gym owners ask us
Can mould be treated with bleach?
On a concrete floor, a registered disinfectant is fine. On the tiles, bleach ages the vinyl and does not reach affected foam. And nothing holds if the water comes back.
Does the whole mat need replacing?
Rarely. Tiles with affected foam are replaced, the others treated, and the cause fixed.
Is it dangerous for members?
Moulds irritate the airways, especially in people with asthma. If in doubt about health, Info-Santé 811.
An outbreak costs more than a cleaning.
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