Bathroom mould is a common problem in Toronto homes — particularly in older houses with limited ventilation, and in apartments and condos where windows are sealed and exhaust fans are small or inadequately maintained. The conditions that cause mould (moisture, warmth, organic material) are inherent to bathrooms. Preventing mould is fundamentally about controlling moisture — removing it before it has time to support mould growth.
Why Toronto Homes Are Particularly Susceptible
Several factors make bathroom mould more likely in Toronto homes specifically:
- Cold winters = poor ventilation — in January, opening a bathroom window to ventilate is impractical. Exhaust fans become the only moisture control mechanism, and many are inadequate or poorly maintained.
- Older housing stock — many Toronto semis and houses were built before exhaust fan requirements were standard. Fans may have been added later in inadequate sizes, or may vent into the wall cavity rather than to the exterior.
- Temperature swings — cold outside walls meeting warm humid shower air create condensation on surfaces that wouldn't get warm in a Toronto winter.
The Most Effective Mould Prevention Measures
1. Run the exhaust fan properly
The exhaust fan must run during and for at least 20 minutes after every shower. Most people turn the fan off when they leave the bathroom — the residual humidity from the shower continues after you leave. The fan needs to continue running to remove it.
If you have a fan without a timer: replace the switch with a timer switch (available at Home Depot or Home Hardware for under $20). This allows you to set a 20–30 minute run time without remembering to come back and turn it off.
Check that your exhaust fan actually vents to the exterior — some are connected to ductwork that terminates in the attic or walls rather than outside, which means they recirculate moist air into the structure. You can confirm by holding a piece of tissue near the vent grille while the fan runs; it should be drawn toward the fan.
2. Squeegee shower walls after every use
A quick pass with a shower squeegee removes the majority of water from shower walls and door glass in about 30 seconds. This single habit reduces the amount of moisture available for evaporation and condensation on surrounding surfaces significantly. Keep a squeegee in the shower — the habit is only sustainable if it doesn't require leaving the shower area.
3. Keep surfaces dry
- Hang wet towels and bathrobes outside the bathroom to dry
- Dry the caulk line between the tub and wall after each use — this is a primary mould location
- Remove standing water from the shower floor if it doesn't drain quickly
4. Clean bathroom surfaces with mould-inhibiting cleaners regularly
Weekly cleaning with a disinfecting bathroom spray (or diluted bleach solution) on tile, grout, and caulk surfaces kills mould spores before they establish colonies. The key is frequency — cleaning once a week prevents the kind of buildup that requires the deep clean described in our grout cleaning guide.
5. Address grout and caulk that is already moulded
Mouldy grout and caulk can be treated (see our guide on deep cleaning bathroom grout), but if the caulk bead has become deeply black and spongy, treatment won't fully restore it — it needs to be removed and replaced. Bathroom caulk should be replaced every 3–5 years in well-maintained bathrooms; more often when mould has established.
When Mould Recurs Despite Prevention
Persistent mould recurrence despite proper ventilation and drying habits can indicate:
- A leak behind the wall or under the tub — moisture from outside the visible surface
- An inadequate exhaust fan for the bathroom size (fans are sized in CFM — cubic feet per minute; a typical bathroom requires 1 CFM per square foot)
- A structural issue: missing or inadequate vapour barrier on an exterior wall
These require investigation and possibly professional remediation beyond cleaning — the mould is a symptom of a moisture intrusion problem.
Bathroom deep cleaning is included in Maidless's Toronto deep cleaning service. Book a Toronto deep clean — HST included.