Medium mould patches in my Ottawa basement, clean or hire?

Health Canada says you can generally clean small and medium sized areas of mould yourself. Medium means more than three patches, or patches greater than one square metre but less than three square metres. If your basement patches fit that description, a DIY clean is reasonable, but read the rest before you start.

Fixing what caused the mould comes first. Mould comes back if the moisture source stays. Before any cleaning, find where the water is entering or condensing and address that first. Once the source is fixed, Health Canada's guidance is that you can clean medium areas yourself. If any single patch is larger than three square metres, that is extensive growth and Health Canada recommends getting professional help.

One thing to check before you touch anything

If your home was built before 1990, raise the asbestos question before cutting or removing any drywall, plaster, ceiling texture or flooring to get at the mould. Health Canada lists older building materials such as cement and plaster, drywall and spackling, and floor and ceiling tiles, and Ontario's guide adds joint compounds and textured paints and coatings. Ontario's guide notes that asbestos was widely used in sprayed-on material and in pipe and boiler insulation until 1973, and that many other asbestos-containing materials continued in use until the mid-1980s. If the remediation involves opening a wall or disturbing any of those surfaces in an older home, have the material tested by a professional before work resumes. Health Canada advises hiring a professional to test and a qualified asbestos removal specialist if asbestos is found.

We found no Ontario statute or regulation that licenses mould remediators or sets indoor mould limits. We found no City of Ottawa permit for mould remediation. If you do hire someone, the things worth confirming in writing are: a clear scope of work describing exactly what gets removed and how the moisture source is being repaired, WSIB clearance (you can search a contractor's current clearance online), and confirmation that no visible mould will remain when the job is done. A post-remediation check should confirm the written scope was followed, the moisture repair is complete, and no visible mould is left.

After the job is done, keep the written contract, the scope of work, and any post-remediation report the contractor provides. Those records show what was found and what was done.