How to Identify Mould
Mould isn’t always visible, but it often leaves subtle signs:|
- A musty or earthy smell in a particular room or enclosed space.
- Discolouration or staining on walls, ceilings, or around vents.
- Peeling paint, bubbling drywall, or warped wood surfaces.
- Persistent condensation on windows or cold surfaces.
In basements, bathrooms, and attics, mould can hide behind drywall, under flooring, or within insulation. If left unchecked, it can spread quickly through the air via microscopic spores.
Source: Health Canada – Addressing Moisture and Mould in Your Home
Why Mould Thrives After Water Damage
Water is mould’s main fuel. When moisture seeps into porous building materials such as wood, drywall, or insulation, it provides the perfect environment for mould to grow. While many homeowners associate “water damage” with flooding, the truth is that most mould issues come from smaller, repeated water events like:
- Overflowing sinks or bathtubs.
- Small pipe leaks behind walls.
- Condensation from poor ventilation.
- Roof or foundation seepage during heavy rain.
These minor incidents often go unnoticed but can create long-term structural damage and invisible air quality issues if the area remains damp.
Source: CMHC – Mould and Your Home
Drying After Water Damage — The Critical Step Many Miss
One of the biggest risks after water damage isn’t when water gets in — it’s when the area isn’t dried completely.
Many homeowners mop up visible water or air out a space for a day or two, believing the problem is solved. In reality, moisture often remains trapped behind walls, under flooring, or within insulation, creating the perfect conditions for mould to grow unnoticed.
Even small events like a minor plumbing leak, an overflowing bathtub, or condensation at the base of walls, can introduce enough moisture for mould to take hold within 24 to 48 hours if not properly dried.
🧱 Insights from Basement Builders
Basement Builders, the leader in basement development in Canada with thousands of completed projects, has seen this scenario time and again.
According to their website, many homeowners underestimate the time it takes for materials like wood to dry fully.
This oversight can lead to hidden structural damage and mould growth behind finished surfaces, often months after the initial water event.
That’s why Basement Builders incorporates TEKSILL in their construction process — a Canadian-engineered sill plate protection that acts as a moisture barrier where wood meets concrete. This innovative product helps prevent water from being trapped under walls, allowing air movement and proper drying at the most vulnerable part of a structure.
By integrating TEKSILL into their builds, Basement Builders not only improve long-term durability but also reduce the risk of hidden mould growth; a step that every homeowner should consider essential in any basement project.
Common Areas Where Mould Develops
Mould tends to form in areas with high humidity, limited airflow, or hidden water exposure:
- Basements and crawl spaces – due to soil moisture and poor ventilation.
- Bathrooms and kitchens – from steam, leaks, and condensation.
- Attics – from roof leaks or trapped warm air meeting cold surfaces.
- Walls and ceilings – especially near plumbing lines or window frames.
- Behind baseboards and flooring – where water can collect unnoticed.
In finished basements, even a small gap between the wall and floor slab can trap moisture — a common source of hidden mould growth.
Mould You Can’t See — But Should Fear
Mould is deceptive. Often, you won’t see patches on walls or ceilings until the problem is well advanced. It typically starts behind drywall, under flooring, or inside wall cavities — places where moisture lingers invisibly. One of the most common yet overlooked areas is the space between the foundation and the sill plate, where trapped moisture can remain unnoticed for long periods and begin spreading through the wall structure.
Many homeowners only realize mould is present once it has produced a distinct musty odour, peeling paint, or visible stains.
Because mould spreads via microscopic spores, it can invade hidden zones — like the wood framing, insulation, subfloor, or sill plate connection — long before it becomes visible. That’s why relying only on sight is risky; prevention and early detection are essential.