Do Not Test the Air, and Do Not Use Bleach

Two things almost everyone does when they find mould are the two things Canadian guidance advises against. Testing the air to find out what it is, and reaching for the bleach.

Health Canada does not recommend testing the air for mould. And the use of chemical disinfectants such as chlorine bleach for remedial purposes is not recommended either.

Why testing tells you nothing useful

CCOHS quotes Health Canada's position directly: in accord with other public health organizations, it does not recommend testing the air for mould, because an air test does not provide information on health and does not address the cause of the mould damage. You do not need to know the type of mould present in order to remove it.

That is a more useful statement than it first appears. The decision tree for mould does not have a branch where the species changes what you do. Visible growth gets removed and the moisture source gets fixed, whatever it turns out to be.

The reason there is no threshold to test against is also stated plainly. Health Canada does not have any numerical exposure limits for mould, on the basis that since people have different sensitivities, it is not possible to establish a safe limit.

So a lab result has nothing to be compared against. Sampling before remediating visually identified growth is not usually necessary.

What is worth measuring is moisture. Moisture meters on drywall and wood tell you whether conditions support growth, which is actionable in a way a spore count is not.

Bleach is the wrong tool on the wrong material

The second instinct fails for a structural reason rather than a chemical one.

CCOHS advises against chemical disinfectants including bleach for remedial purposes, noting they can pose health concerns for people in occupied parts of the building. Health Canada likewise advises against using bleach to clean up mould.

The deeper problem is porosity. On a porous material the growth extends below the surface, so wiping the face with anything leaves the colony intact and adds water to a material that already has a moisture problem.

Canadian practice splits materials three ways. Non-porous materials such as metal, glass and hard plastic can be cleaned and reused, and soap and water is what is recommended for that. Semi-porous materials such as wood and concrete can often be cleaned if structurally sound. Porous materials with growth are removed.

Porous means drywall, ceiling tile, carpet, insulation, fabric, books and cardboard. Those are discarded rather than treated, and no product changes that.

Where removal is the answer, the guidance is to take the porous substrate out to a minimum of 30 centimetres beyond the visible contamination in all directions, because the edge of what you can see is not the edge of the growth.

The window is 48 to 72 hours

This is the number that decides whether you have a drying job or a remediation job.

Mould has been shown to grow on materials that are wet for 48 to 72 hours. Dry the building inside that window and there may be nothing to remediate; miss it and the work changes character entirely.

That makes the response to a leak, a flood or a burst line a race rather than a scheduling exercise, and it is the single highest-return thing a property maintenance or restoration crew can get right.

It also means a slow leak behind a wall has been producing growth for as long as it has been leaking, which is why hidden mould is routinely more extensive than the visible patch suggested.

Look for it where water goes rather than where it shows: behind walls, in conduits and chases, under flooring, above ceiling tiles, inside wall cavities and around window and roof penetrations.

Fixing the moisture source is not optional. Removing growth without correcting the cause produces the same job again in a few months.

British Columbia wants a Notice of Project

There is a specific regulatory trigger in BC that catches contractors who treat mould as ordinary cleanup.

WorkSafeBC guidance provides that a Notice of Project must be submitted for work involving the remediation, cleanup or demolition of mould-contaminated areas where the total surface area affected is greater than 10 contiguous square metres, which is about 100 contiguous square feet.

That is not a large area. A single wall in a flooded basement clears it comfortably, and a crew that has started work without filing has missed a step before the first sheet came off.

Health Canada also advises that professional assistance should be sought for remediation of large mould problems, which is a separate judgement from the notification threshold.

At the small end, Health Canada's household guidance treats a small area as three or fewer patches with a combined area of no more than one square metre, with expert assessment recommended for medium areas and professional assessment for large ones.

Those are decision aids rather than universal rules, and the workplace question is governed by the occupational regulation where you operate.

The equipment, and the vacuum problem

Health Canada's recommended protection for mould cleanup is specific and modest: safety glasses or goggles, a well-fitting disposable N95 respirator, and disposable gloves.

This is one of the situations where an N95 is the right class of protection, because the hazard is airborne particulate. The qualifier doing the work in that sentence is well-fitting, and our guide to respirator fit testing under CSA Z94.4 covers why a seal decides whether the rating means anything.

Larger jobs escalate the protection considerably, with full-face respirators and disposable full-body clothing used on higher-level abatement, and that selection belongs with someone experienced in mould remediation rather than with a product page.

Eye protection matters because spores and dust go up, covered in our safety glasses guide, and changeable clothing keeps contamination out of vehicles and homes, covered in our comparison of coveralls and bib overalls.

Gloves cover both the handling and whatever cleaning product is in use, covered in our guides to work gloves and choosing chemical resistant gloves.

One control worth naming because it is counterintuitive: vacuuming may increase exposure by making spores airborne. Central vacuums exhausting outside, or units with HEPA filtration, minimize that. An ordinary shop vacuum is a spore distributor.

Dust suppression helps as well. Lightly misting mouldy material with water before disturbing it, or taping plastic sheeting over it, keeps spores from going up when the sheet comes off.

Containment and what gets recorded

Beyond the smallest jobs, keeping spores inside the work area is what protects everyone who is not doing the work.

Canadian guidance on investigating and remediating mould in workplaces describes an escalating approach, with containment or isolation measures used to prevent worker exposure and stop the spread of mould from the remediation zone into adjacent areas.

Practically that means sealing the area, controlling access, and considering whether occupants need relocating while the work runs. Relocation decisions take account of the degree of contamination, the extent of the work and the sensitivity of the people involved.

Someone should be named as responsible for the remediation rather than it being everyone's job, which is the same principle that makes a fire watch or a prime contractor designation work.

Workers should clean up at the end of the work rather than carrying contamination out with them, and the work area and the routes workers use to leave it should be cleaned down with a damp cloth or HEPA vacuum.

Disposal of mouldy material has no special requirements in most cases, though bagging it before carrying it through occupied space is the obvious courtesy and the obvious control.

Old buildings carry more than mould

This is the point that links mould work to the rest of the renovation hazard picture.

Demolition and removal work in an older building can expose workers to lead, asbestos and silica alongside the mould, and a crew focused on one hazard routinely disturbs the others.

Water-damaged drywall in a pre-1990 building may contain asbestos in the joint compound. Painted surfaces in a building of the right vintage may be leaded. Cutting and breaking anything cementitious produces respirable silica.

Those have their own and considerably stricter requirements, including licensed abatement for asbestos in British Columbia, and they are not addressed by an N95 and a pair of gloves.

The practical rule is the same one that applies across renovation work: establish what is in the material before disturbing it, rather than discovering it afterward. Our guide to PPE for painters and drywallers covers the adjacent exposures in finishing work.

Worker health effects from mould exposure itself include allergic reactions, asthma, pneumonitis with flu-like symptoms, upper airway infections and sinusitis, and sensitivity varies considerably between individuals.

For the wider kit see the complete PPE checklist for Canadian workers, our guide to PPE requirements for Canadian construction sites, our guide to who pays for PPE in Canada, our guide to CSA Z1220 first aid kit requirements and our guide to CSA certified versus CSA compliant.

Frequently Asked Questions

Should I test the air to identify the mould?

Health Canada does not recommend it. An air test does not provide information on health and does not address the cause of the damage, and you do not need to know the type of mould in order to remove it. Sampling before remediating visually identified growth is not usually necessary.

Why is there no exposure limit for mould?

Health Canada does not have numerical exposure limits, on the basis that since people have different sensitivities it is not possible to establish a safe limit. That is also why a lab result has no threshold to be compared against.

Should I use bleach?

Canadian guidance advises against it. CCOHS does not recommend chemical disinfectants including chlorine for remedial purposes, noting they can pose health concerns for occupants, and Health Canada advises against using bleach to clean up mould. Soap and water is what is recommended for non-porous materials.

What gets cleaned and what gets thrown out?

Non-porous materials such as metal, glass and hard plastics can be cleaned and reused. Semi-porous materials such as wood and concrete can often be cleaned if structurally sound. Porous materials with growth, including drywall, ceiling tile, carpet, insulation and fabric, are removed, cut back a minimum of 30 centimetres beyond the visible contamination.

How fast does mould start growing?

Mould has been shown to grow on materials that are wet for 48 to 72 hours. Drying a building completely inside that window can mean there is nothing to remediate, which makes the speed of the response to a leak or flood the highest-return decision available.

Is there a notification requirement in British Columbia?

Yes. WorkSafeBC guidance provides that a Notice of Project must be submitted for remediation, cleanup or demolition of mould-contaminated areas where the total surface area affected is greater than 10 contiguous square metres, roughly 100 contiguous square feet. That is less area than most people assume.

This guide is general workplace safety information, not remediation or medical advice. Mould remediation requirements, notification thresholds and worker protection obligations are set by provincial and territorial regulation and differ between jurisdictions. Large or extensive mould problems should be assessed and remediated by qualified professionals. Older buildings may also contain asbestos, lead or silica, which carry separate and stricter requirements. Anyone experiencing respiratory symptoms should be assessed by a healthcare professional.