Where to look for mold

Mold in the Workplace: How to Report It and What Happens Next

You have seen the staining behind the filing cabinet, or the corner of the ceiling tile that keeps going brown. You have mentioned it. Nothing has happened. Reporting mold at work is a defined process in Ontario and Quebec, and it puts obligations on your employer once you start it.

This page walks through what to write down, who to tell first, what the law actually requires of an employer, and what to do if the answer is still nothing. Written for the person raising it, not the company receiving it.

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The short version. Write down what you see and when you saw it, with photos and dates. Report it in writing to your supervisor so there is a record. If your workplace has a joint health and safety committee, send the same note to the worker member. If nothing changes, you can contact the provincial regulator directly. In Ontario your employer has a general duty under the Occupational Health and Safety Act to take every precaution reasonable in the circumstances for your protection, and it is against the law for them to punish you for raising it.

Are you the employer or facilities lead who received the complaint? Skip ahead to what to do next, or book a free virtual inspection to get an independent read before you commit to anything.

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How to tell whether it is actually mold

Before you report anything, it helps to be specific about what you are looking at. A vague report is easy to dismiss. A dated photo of a defined stain with a description of the smell is not.

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You can see it

Speckling or fuzzy patches on ceiling tiles, drywall, window frames or the back of storage areas. Colour is not a reliable guide to what it is, so describe what you see rather than naming a type.

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You can smell it

A persistent earthy or musty smell in one part of the building, strongest in the morning before the ventilation has been running, often means growth somewhere out of sight.

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There is a water history

A roof leak, a burst pipe, a flooded basement level or a chronically leaking air conditioning unit. If the area got wet and stayed wet, growth follows within a couple of days.

Where it usually turns up in a commercial building

Ground floors and basement levels, because that is where water collects. Anywhere near an air conditioning unit, because the condensate tray and drain line are a common failure point. Kitchens and staff rooms, where forgotten food and a poorly sealed sink do the rest. Behind and under storage, where nobody looks and air does not move.

The ventilation system matters because it can move spores from a small hidden source into occupied areas, which is why a problem can present far from where it started.

Workplace ventilation grille with surface mold growth

What not to do

Do not disturb it. Scraping, wiping or spraying a patch before anyone has looked at it makes the assessment harder and can spread the problem into air that other people are breathing.

Do not test it yourself. Health Canada’s residential indoor air quality guideline on moulds states that in the absence of exposure limits, results from tests for the presence of fungi in air cannot be used to assess risks to the health of building occupants. What matters is finding the moisture and removing the growth, not identifying the species.

What to write down before you report it

Documentation is what turns an offhand comment into something on the record. Keep it factual and keep a copy somewhere that is not your work computer.

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Dated photographs

Wide shot for context, close shot for detail. Photograph any water staining, damaged ceiling tiles or damp patches nearby, even if they look unrelated.

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A simple timeline

When you first noticed it, whether it has grown, and any water event you know about. Approximate dates are fine. Write what you actually know, not what you assume.

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Exact location

Floor, room, and a fixed reference point such as a column number or the nearest door. Facilities teams work from building plans, so a precise location gets acted on faster.

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Who you already told

Names, dates and what was said. If you raised it verbally and nothing happened, that history is the reason a written report carries more weight than a second conversation.

On how you are feeling. If you have noticed something that seems to ease when you are away from the building, note the dates and the pattern, and take it to a healthcare professional. That is their call to make, not ours and not your employer’s. Keep the health question and the building question on separate tracks: your report should describe the building.

How to report mold at work: five steps

This is the escalation path in Ontario. Quebec follows the same shape with a different regulator, covered further down.

Document it

Photographs, dates, location and any water history, as set out above. Do this before you raise it, so your first report is already specific.

Tell your supervisor, in writing

Email is ideal because it timestamps itself. Describe what you saw and where, attach the photographs, and ask what the next step will be. A verbal mention leaves no record and is the most common reason these reports stall.

Copy your joint health and safety committee

Under the Occupational Health and Safety Act, a joint health and safety committee is required at a workplace where twenty or more workers are regularly employed. It has at least one worker member whose job is to carry concerns like this one. Smaller workplaces generally have a health and safety representative instead. Ask your supervisor or HR who yours is; they are required to be identifiable.

Contact the regulator if nothing moves

In Ontario that is the Ministry of Labour, Immigration, Training and Skills Development, which takes complaints from workers directly and can send an inspector. In Quebec it is the CNESST. In a federally regulated workplace such as a federal department, bank, airline or telecom, it is the federal Labour Program instead. If you are in a union, your health and safety representative usually knows this route well and can move faster than you can alone.

Ask for an independent assessment

At some point somebody has to actually look at the building. An independent assessment gives the employer a defensible basis for a decision and gives everyone else something better than opinion. This is the point where a company like ours normally gets called, usually by the employer rather than by you.

What the law requires of your employer

Ontario’s Occupational Health and Safety Act does not mention mold by name. It does not need to. The general duty clause is broad enough to cover it, and the province applies that duty to mould directly in its published alert on mould in workplace buildings.

The general duty, section 25(2)(h)

An employer must “take every precaution reasonable in the circumstances for the protection of a worker.” This is the clause that makes indoor air quality an employer’s problem even without a mold-specific regulation. Inspectors enforce it.

Joint health and safety committees, section 9(2)(a)

“A joint health and safety committee is required, (a) at a workplace at which twenty or more workers are regularly employed.” The committee is your internal route, and it exists precisely so that concerns do not depend on one manager’s goodwill.

Protection from reprisal, section 50(1)

“No employer or person acting on behalf of an employer shall, (a) dismiss or threaten to dismiss a worker; (b) discipline or suspend or threaten to discipline or suspend a worker; (c) impose any penalty upon a worker; or (d) intimidate or coerce a worker, because the worker has acted in compliance with this Act or the regulations or an order made thereunder, has sought the enforcement of this Act or the regulations or has given evidence in a proceeding in respect of the enforcement of this Act or the regulations.” Two things matter there. Raising a health and safety concern is acting in compliance with the Act. And taking it to the Ministry is explicitly covered by the words “has sought the enforcement”, so escalating outside your employer is protected too.

The right to refuse, section 43(3)(b)

A worker may refuse to work where they have reason to believe that “the physical condition of the workplace or the part thereof in which he or she works or is to work is likely to endanger himself or herself.” This right is real, and it is narrower than people expect. It carries a formal process and it is difficult to sustain on a mold complaint without supporting documentation. Understand that it exists; get advice from your union or an employment lawyer before you rely on it. Nothing on this page is legal advice.

If you work in Quebec

Quebec workplace health and safety is administered by the CNESST rather than by Ontario’s ministry, so the sections quoted above do not apply in Quebec and the process is handled through that body instead. Start on the CNESST site for the current process and your options. If you are in a union, raise it there at the same time.

If your workplace is federally regulated

Federal departments and agencies, banks, airlines, railways, interprovincial trucking and telecoms fall under federal rather than provincial rules, and complaints go to the federal Labour Program. The internal steps are the same: document it, report it in writing, involve your committee.

Did you know?

Mold needs only a damp surface and roughly 24 to 48 hours to establish. That is why a slow leak nobody prioritised in March can be a visible problem by the time anyone reports it. More in our mold statistics page.

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What a proper response looks like

If your employer is taking it seriously, this is roughly what you should expect to see. It is also a fair yardstick for judging whether the response you got was adequate.

Find the water first

Growth is the visible result of a moisture problem. Cleaning the surface without fixing the leak, the condensation or the drainage guarantees it comes back, usually in the same spot.

Scope it before touching it

How much, how far it has spread, and whether it has moved into the wall cavity or the ventilation system. That determines whether this is a maintenance job or a contained remediation.

Contain the work area

Anything beyond a small surface patch needs the area isolated and negative air pressure, so that removing the growth does not distribute it through the rest of the floor.

Verify and document

Photographs of the work and a written report at the end. A verbal all-clear is not documentation, and the committee is entitled to see what was actually done.

Containment set up for mold remediation in a workplace

Why the size of the area changes everything

A patch smaller than a sheet of paper on a hard surface is usually maintenance work, done with protective equipment and the area cleared of people. Once it covers a few square metres, or once it is inside a wall or a duct, it needs full containment and trained crews.

The distinction matters to you because it determines whether the work can happen around you or whether the area has to be emptied first. Ask which category your employer thinks it falls into, and on what basis.

If an employee has raised this with you

You have a written complaint, a photograph, and an obligation to respond. The useful next step is an independent assessment that tells you what is actually there, so that whatever you decide is based on findings rather than on how alarming the photo looked.

We work with employers, building owners and facilities teams across Ontario and Quebec. We collect the samples and an accredited third-party laboratory analyses them, which keeps the finding independent of the company quoting the remediation. Reconstruction is delivered by partners and quoted separately.

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If you are the facilities or property manager responsible for a workplace, see our mold and indoor air quality services for business and institutions. Building owners and commercial landlords managing multiple properties can review our mold and indoor air quality services for commercial real estate, or our services for property managers for residential portfolios.

Frequently asked questions about mold in the workplace

Put it in writing. Email your supervisor with dated photographs, the exact location, and any water history you know about, and ask what the next step will be. Copy the worker member of your joint health and safety committee if your workplace has one. A written report creates a record and a date, which a verbal mention does not, and that record is what matters if you have to escalate later.

In Ontario, no. Section 50(1) of the Occupational Health and Safety Act says no employer shall dismiss, discipline, suspend, penalise, intimidate or coerce a worker because the worker has acted in compliance with the Act, sought its enforcement, or given evidence in a proceeding about it. Reporting a health and safety concern is acting in compliance with it, and so is taking the matter to the Ministry. In Quebec the process runs through the CNESST and you should check the current position on their site. If you believe you have been penalised for reporting, that is a separate complaint and worth taking to your union or an employment lawyer promptly, because time limits apply.

There is no mold-specific regulation in Ontario, and no numeric exposure limit for mold has been set in Canada. Health Canada takes the position that the variation in how people respond means exposure limits cannot be derived at all. What applies instead is the general duty in section 25(2)(h) of the Occupational Health and Safety Act, requiring an employer to take every precaution reasonable in the circumstances for the protection of a worker, and the province applies that duty to mould directly in its alert on mould in workplace buildings. The absence of a numeric limit is not a loophole; it means the standard is reasonableness, judged after the fact by an inspector.

Quebec runs its own occupational health and safety system, administered by the CNESST rather than by Ontario’s Ministry of Labour, so the Ontario sections quoted on this page do not apply there. The practical steps at the start are the same wherever you are: document what you see, report it in writing, and keep a copy. For the Quebec process itself, including how complaints are handled and what your options are, start on the CNESST site at cnesst.gouv.qc.ca. If you are in a union, raise it there at the same time.

Ask HR or your supervisor directly, and check the health and safety noticeboard, where the names are usually required to be posted. A joint health and safety committee is required in Ontario at workplaces with twenty or more workers regularly employed. Smaller workplaces generally have a health and safety representative instead. In a unionised workplace, your union will know immediately.

They can delay, and many do, but ignoring it is not a safe position for them. The general duty clause applies whether or not they respond to you, and a worker can take a complaint to the provincial regulator without the employer’s agreement. If your written report has gone unanswered, that silence is itself part of the record. Give a reasonable interval, follow up in writing, then escalate.

A musty smell with nothing visible usually means the growth is somewhere you cannot see it: inside a wall cavity, above a ceiling, under flooring, or within the ventilation system. Absence of a visible patch is not evidence of absence. Ask for the moisture history of that area and whether anyone has looked behind the finishes. This is exactly the situation an independent assessment is for, because it looks past the surface rather than relying on what is on show.

Ontario’s Occupational Health and Safety Act gives a worker the right to refuse work where they have reason to believe the physical condition of the workplace is likely to endanger them. The right exists, and it is narrower and more procedural than most people expect, with defined steps that follow once you invoke it. It is not a step to take casually or alone. Speak to your union representative or an employment lawyer first. Nothing on this page is legal advice.

Generally no, and not because testing is useless. Health Canada’s guideline on moulds states that in the absence of exposure limits, results from tests for the presence of fungi in air cannot be used to assess risks to the health of building occupants. A test tells you what was in the air at one spot at one moment; it does not tell you whether a building is safe. Assessment is most useful when it is finding the moisture source and the extent of growth, which is a building investigation, not a single sample. It is also normally the employer’s responsibility to commission, not yours.

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