Mold on Slab Foundations
Slab-on-grade homes do not have a basement to hide moisture in, so water vapour comes up through the concrete instead. Older slabs frequently have no vapour barrier beneath them, which means moisture moves continuously upward into flooring and the bottom of walls.
Signs to look for
- Flooring lifting, cupping or bubbling
- Damp spots on the slab that reappear
- Musty smell at floor level
- Staining at the base of walls
- Carpet tack strips corroding
What usually causes it
- No vapour barrier under the original slab
- Plumbing leaks in or under the slab
- Poor exterior grading
- Impermeable flooring trapping vapour
- Downspouts discharging at the slab edge
Removing the growth without eliminating the water source simply resets the clock. Every report we write identifies the moisture source, because that is the finding that determines what it actually costs you to fix.
How we investigate it
Locate the moisture
Thermal imaging and moisture meters map the full extent of wet material, including behind finishes.
Establish the source
Groundwater, plumbing, condensation and ventilation failures all look similar at the surface and need completely different fixes.
Sample if it changes the plan
Air sampling with an outdoor control where growth is hidden; surface sampling where it is visible.
Document and hand off
A written report you can hand to a contractor, an insurer or a landlord — and independent clearance testing afterwards.
Related
Common questions
What causes mold on slab foundations?
No vapour barrier under the original slab; Plumbing leaks in or under the slab; Poor exterior grading.
How do I know if I have mold on slab foundations?
Flooring lifting, cupping or bubbling; Damp spots on the slab that reappear; Musty smell at floor level.
Can I clean it myself?
Under roughly ten square feet with a known, corrected water source, most homeowners can clean it safely with gloves, an N95 and good ventilation. Above that, or where HVAC is involved, where the water was contaminated, or where someone in the household is immunocompromised, containment matters because disturbing growth spreads it through the building.
Will it come back after cleaning?
Yes, if the water source is still there. This is the single most common reason people call us twice. Cleaning removes what has grown; only correcting the moisture stops it regrowing.
Do I need a lab test for this?
Not always. If growth is visible and the cause is obvious, a laboratory result rarely changes what you should do. Testing earns its cost when the source is hidden, when documentation is needed, or when you want to verify a remediation job.
Get a straight answer about your building
We test, document and verify. We never sell remediation, so we have no reason to find a problem you do not have.