How do I know if mold is behind drywall?
Mold behind drywall often shows up as a musty smell, stains or discolouration, bubbling paint, soft or warped wall sections and a history of leaks. A moisture meter and a thermal camera can confirm damp inside the wall, and small inspection openings let a professional check without large demolition.
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The clues you can see and smell
- A persistent musty or earthy smell in one room that returns after airing
- Stains in yellow, brown or dark patches, often near corners, ceilings and baseboards
- Paint or wallpaper that bubbles, peels or cracks
- Drywall that feels soft, swollen or crumbles under light pressure
- Condensation or dampness on nearby windows and walls
- A history of leaks from a roof, a window, a bathroom or a burst pipe
Why a wall can hide a problem
Drywall hides pipes, insulation and framing, and moisture that gets in has nowhere to go. A slow plumbing leak or a window that has leaked for years can keep the cavity damp and grow mold on the back of the board without any mark on the face. In Toronto, older homes, finished basements and bathrooms with poor ventilation are the usual places.
Not every stain means mold, and a clean wall does not always mean there is none. That is why an inspection relies on more than looking.
How a professional checks
- Moisture readings.A moisture meter shows whether the wall material is wetter than it should be.
- Thermal imaging.A thermal camera shows cold, damp areas behind the surface without cutting into it.
- Small inspection openings.A small cut in a hidden spot lets us look directly at the back of the drywall and the insulation.
- Sampling when useful.Air or surface sampling can add information, and we explain when it is worth doing.
What to do if you suspect it
Do not tear open the wall yourself, as that can spread spores through the house. Photograph the signs, note when the smell began, and find and fix any leak you know about. Call for an assessment so the wall can be checked with the right tools. In an apartment or condo, see our condo page for how access and building rules are handled, and our landlord and tenant page if the problem involves a rental.
Common hiding places in Toronto homes
Look behind and around bathroom walls near tubs and showers, below windows that leak or sweat, along exterior basement walls, under kitchen sinks and in corners of top-floor ceilings below the roof. Older houses with poorly sealed windows and condos with leaks from the unit above add to the list. If you smell mold in only one room, start your search in that room's walls and ceiling.
Related questions
Can I test the wall myself?
Home kits can detect that mold is present but not where it is or how much, so they rarely answer the real question.
Will you have to open the whole wall?
Usually not. We check first and open only what the readings point to.
Is the assessment free?
Yes, it is free and you receive a written scope and price.
Request a quote
Tell us what you need and we will get back to you. In a hurry? Calling is fastest.
Call to check a wall for mold
Call us any day. The assessment is free, and you get a written scope and price before any work begins.
Call now (416) 272-3881