Professional mould remediation follows a fixed order: find and fix the moisture source, contain the area, dry the materials, remove the mould and damaged materials, clean with a HEPA vacuum, confirm the result, then rebuild in a way that keeps moisture out. Skipping or reordering these steps is why mould comes back. Below we walk through each step as it happens on a real job, what you should do before the crew arrives, and what affects the timeline.
TL;DR
- Remediation order: fix the water problem, contain, dry, remove, HEPA-clean, verify, rebuild. Killing mould with a spray alone is not remediation.
- Call a professional for a patch over 3 m² (Health Canada), mould that returns after cleaning, flood or leak water, or suspected hidden mould.
- Water damage needs drying within 24 to 48 hours, because mould can start growing in 48 hours.
- Duration depends on the size of the area, the moisture source and the rebuild. Ask for a written scope and a clearance step.
- Our published ranges for Ottawa: $500 to $1,500 for a small contained area, $2,000 to $6,000 for a single room or bathroom.
Table of Contents
- What mould remediation actually is
- The professional mould remediation steps
- How long does mould remediation take?
- What mould remediation costs in Ottawa
- How to prepare before the crew arrives
- Our perspective on remediation
- Book an assessment in Ottawa
- FAQ
- Sources
What mould remediation actually is
Remediation is more than cleaning what you can see. Health Canada says indoor mould growth should be removed and the underlying water or moisture problem fixed first. Without the second part, any cleanup is temporary.
The size of the problem decides who does the work. Guidance differs a little between provinces and agencies:
- Health Canada says a qualified professional is needed for a single patch larger than 3 m², mould that returns after cleaning, contaminated flood or leak water, suspected hidden mould, or flooding into wall, ceiling or floor cavities.
- The Government of Québec is more cautious: for surfaces over 1 m², numerous or hard to clean, or if mould comes back, call a specialized firm.
- Alberta Health Services describes small areas (1 to 3 patches, each under 1 m²) as usually manageable by a homeowner, medium areas as a judgment call with proper protective equipment, and large areas (over 3 m² of dense mould) as a job for a professional.
If you are near the line, the safer reading is the lower number. Hidden mould behind a tile wall or under a vanity is rarely small once it is opened up. For more on the choice between a cleanup and a full job, see our guide on remediation versus removal.
The professional mould remediation steps
The sequence below follows the Canadian guidance from the National Collaborating Centre for Environmental Health (NCCEH) and the Ontario-based Environmental Abatement Council of Canada guidelines. It is the order we work in on our own projects.
Step 1: Inspect and find the moisture source
Every job starts with finding where the water comes from: a roof leak, a failed bathroom fan, a foundation crack, a plumbing line, a flooded basement or high indoor humidity. NCCEH describes remediation as starting with identifying and eliminating the moisture source. If the source stays, the mould returns.
The inspection also looks at how far the growth goes. Mould can sit behind drywall, under flooring and above ceiling tiles, which is why Health Canada lists suspected hidden mould as a reason to bring in a professional.
Sampling is a separate question. Alberta Health Services notes that air testing is usually not recommended, especially when you can see the mould. Testing and lab analysis has its place when the source or type of growth is unclear. We publish a range of $300 to $600 for testing and lab analysis.
Step 2: Set the scope by level
The University of Ottawa’s mould control program recognizes three main levels of remediation, based on the EACO Mould Abatement Guideline (2015) and Canadian Construction Association guidelines. Level I covers small isolated areas under 10 ft² (1 m²). Larger areas move into higher levels with stricter containment and protection.
The level sets the containment, the protective equipment and the cost. A written scope that states the level and the area in square metres is the clearest sign you are comparing like with like between quotes.
Step 3: Protect people and contain the area
Containment limits the spread of spores to the rest of the house. In practice that means plastic sheeting sealed over the work area, closed doors and vents, and controlled entry and exit. NCCEH notes containment is used to limit spread during removal.
Workers are protected too. The EACC guidelines require training in mould hazards, NIOSH-approved respirators, respirator pre-screening under CSA Standard Z94.4-11 and fit-testing for each respirator type. The same guidelines say workers with a history of significant allergic disease, such as asthma, or a possibly weakened immune system should speak to an experienced physician about whether mould work poses an unacceptable risk.
For occupants, Health Canada says infants, children, seniors, pregnant people and people with respiratory conditions such as asthma should stay away from the area during cleanup, and pets too. Plan where they will be during the work.
Step 4: Dry the area and the materials
Drying comes before and during removal. NCCEH describes drying materials and contents as part of the sequence. Time matters here: Ottawa Public Health says mould begins to grow within 48 hours and an immediate response within 24 to 48 hours limits growth. The Government of Québec gives the same 24 to 48 hour window for cleaning and drying water damage.
If the damage came from a spill or leak on a hard floor, the first hours matter just as much. This explainer on vinyl floor water damage covers what happens to flooring when moisture gets under it and what to do in the first day.
Step 5: Remove mould and damaged materials
This is the physical removal. The rule of thumb differs by material:
- Porous materials such as carpet, mattresses, fabric and heavily wet drywall or insulation are discarded rather than cleaned. Health Canada and the Government of Québec both say so.
- Hard, non-porous surfaces such as tile, glass and sealed metal can be cleaned with an unscented soap solution and dried quickly.
- Structural wood is handled by the level of growth and what the scope calls for.
A point that surprises many homeowners: spraying a biocide is not the cleanup. NCCEH says the use of fungicides and antimicrobials is controversial because of toxicity concerns and uncertain effectiveness, and that dead mould fragments can still cause reactions. Biocides are needed mainly where contaminated water such as sewage or floodwater is present. Alberta Health Services goes further in its fungal air testing requirements: treatment with a biocide or bleach alone is not acceptable, and mould, live or dead, requires removal and surface cleaning.
If an older house is involved, materials need a check before they are disturbed. Alberta Health Services points out that some buildings built before the mid-1990s may contain asbestos. We hold abatement licensing as well as remediation experience, so we can test suspect materials before demolition begins rather than after. See our abatement services for how that works.
Step 6: HEPA vacuum and wipe down
After bulk removal, the EACC guidelines require that surrounding areas be cleaned with a HEPA vacuum (no other type of vacuum can be used) and that non-porous surfaces be wiped with a detergent solution. A disinfectant is required where the area was contaminated by something like a sewage flood. NCCEH describes final cleaning as damp wiping and HEPA vacuuming.
Step 7: Check that the work is done
Before the containment comes down, someone should confirm the job. NCCEH says clearance should confirm that moisture problems are addressed, mould removal is complete, and no visible mould, damaged material, dust, debris or mouldy odours remain. Checks can include visual and smell inspection, moisture readings, glove tests and airborne mould sampling. On larger projects, NCCEH calls for independent post-remediation verification.
Our guide to the mould clearance test explains what that looks like for a homeowner, and why a clearance certificate matters if you are holding back part of a contractor’s payment (see our note on holdbacks).
Step 8: Rebuild and prevent a repeat
NCCEH states that rebuilding must be done in a way that prevents future mould growth, and that the order of mould work and water repair can be complex. Rebuilding is where a general contractor’s role matters, because the same crew can open the wall, remove the mould, fix the cause and close it up. Mould-resistant materials can help in basements and bathrooms: see our piece on mould resistant renovation materials.
Afterwards, keep the home dry. Health Canada recommends relative humidity between 30% and 50%, exhaust fans, and a dehumidifier where needed. NCCEH adds that surfaces need to stay clean and dry, with regular visual checks. SAFE Work Manitoba suggests a follow-up evaluation about three to six months after remediation to check for recurring mould.
How long does mould remediation take?
No reputable contractor can give a fixed number of days without seeing the space. What we can say is what moves the timeline:
- Size and level of the area: a small contained patch is a different job from a whole basement wall.
- Hidden damage: once drywall is opened, the true extent often becomes clear.
- Drying time: wet materials must be dry before they are closed up.
- Moisture repair: a plumbing, roof or foundation fix has to happen first or alongside.
- Verification: clearance checks and any lab turnaround.
- Rebuild: drywall, flooring and finishing take longer than the removal in many homes.
The time that matters most is the first 48 hours after water damage, not the length of the job. If a leak or flood has just happened, act now and call us for a quote afterwards. Our estimates come back within 24 hours, and the written scope sets out the stages and timing for your specific space.
What mould remediation costs in Ottawa
Here are our published ranges for mould work. Your written quote lists each line item.
| Job type | Published range |
|---|---|
| Small contained area | $500 to $1,500 |
| Single room or bathroom | $2,000 to $6,000 |
| Basement or flood-related | Quoted after assessment |
| Testing and lab analysis | $300 to $600 |
Basement and flood jobs are quoted individually because the extent of wet material varies so much. More on that in our basement mould remediation guide.
How to prepare before the crew arrives
Preparation is mostly about safety and stopping the problem getting worse. Health Canada’s steps are to discard mouldy or damaged materials, vacuum with a HEPA filter, clear wet areas, dry them with fans and a dehumidifier, and isolate the area with plastic sheeting if necessary. If you cannot tell where the water is coming from, get help.
A few practical points:
- Stop the water. Shut off the supply, patch what you can and document the damage with photos for your insurer.
- Keep people and pets out. Follow the Health Canada guidance above, especially for children, seniors and anyone with asthma.
- Move belongings out of the room if it is safe to do so, and leave porous items that are already mouldy for the crew to assess.
- Do not disturb large patches. Scrubbing or sanding spreads spores.
- Wear protection if you must work near it. Ottawa Public Health recommends goggles without ventilation holes, a disposable N95 mask (not a regular dust mask) and disposable gloves reaching mid-forearm.
What not to clean mould with
Bleach is the common mistake. Health Canada advises against using it, and the Government of Québec says it is not necessary, other than to disinfect objects that may touch the mouth, such as children’s toys. Ottawa Public Health warns that bleach must never be mixed with other cleaners or products containing ammonia, because toxic fumes can result, and that any disinfectant use needs ventilation with air exhausted outdoors.
Our perspective on remediation
Most of the mould calls we get in Ottawa have the same story: someone cleaned it, it came back, and the water problem was never fixed. We think a remediation job is only finished when the moisture source is dealt with, the work is documented, and the wall is closed up properly.
That is why we do the abatement, demolition and rebuild under one roof. We are licensed and insured for abatement, we have more than 25 years of local experience, and our quotes are itemized line by line so you can see what each stage covers. In older Ottawa houses we check for asbestos or other hazards before we open anything up.
If you are unsure whether your mould is a small cleanup or a full remediation, send us photos and we will give you a straight answer, with an estimate back within 24 hours.
Jason
Book an assessment in Ottawa
If you have mould over a small patch, repeated mould, or water damage from a leak or flood, we can assess it, set the scope and handle the removal and rebuild. See our mould remediation services for scope and price ranges, or read our Ottawa homeowner’s guide.
Contact us through hmjcontracting.com for a free estimate, itemized and delivered within 24 hours.
FAQ
When do I need a professional instead of cleaning it myself?
Health Canada says to call a professional for a single patch over 3 m², mould that returns after cleaning, contaminated water, suspected hidden mould, or water in wall and floor cavities. Québec sets the threshold lower, at 1 m². If you are close to the line, treat it as a professional job.
Can I just spray the mould with bleach or an antimicrobial?
No. Health Canada advises against bleach, and Alberta Health Services says biocide-only treatment is not acceptable remediation. The mould has to be physically removed and the area cleaned, and the moisture source fixed.
How soon does mould start to grow after water damage?
Mould can begin to grow within 48 hours on wet materials, according to Health Canada and Ottawa Public Health. Dry everything within 24 to 48 hours where you can, and discard porous materials that stayed wet.
How do I know the remediation worked?
A proper job ends with a clearance check: no visible mould, damaged material, dust or mouldy odour, with moisture problems resolved. Larger projects call for independent verification. A follow-up check after three to six months is also suggested.
Sources
- Guide to addressing moisture and mould indoors, Health Canada
- Finding and eliminating mould from your home, Gouvernement du Québec
- Mouldy Homes and Buildings: Managing Indoor Mould, Alberta Health Services
- Mould Remediation, NCCEH
- EACC Mould Abatement Guidelines, 3rd edition (2015)
- Mould Control and Water Damage Restoration Program, University of Ottawa
- Mould, Ottawa Public Health
- Fungal Air Testing, Investigation and Reporting, Alberta Health Services
- Investigation, Assessment and Remediation of Mould, SAFE Work Manitoba
- Vinyl floor water damage