In Quebec, especially in homes built 40 to 50 years ago, pyrite and pyrrhotite can pose serious risks to foundations and overall property value. Whether you’re buying, selling, or currently owning, understanding how to spot, test, and deal with pyrite can protect both your investment and peace of mind.
What Is Pyrite and Why Is It a Problem?
Pyrite is a naturally occurring mineral sometimes found in the crushed stone (backfill) used beneath concrete slabs in home construction. When exposed to oxygen and moisture, pyrite reacts chemically, producing sulphuric acid and causing the backfill to expand. This can lead to cracking, heaving, and damage to foundations—especially in basements and garages.
Similarly, pyrrhotite, another mineral, can cause structural issues when it crystallizes, putting pressure on concrete and forming cracks over time.
Signs of Pyrite Damage
- Cracks in basement floors or foundation walls
- Uneven or heaving floors
- White powder near cracks (sulphate crystallization)
- Sticky doors or windows
- Increased humidity in the basement
Where Is Pyrite Most Common?
Areas around Montreal’s South Shore, the East End, and West Island—especially Montérégie—are known to be at risk due to backfill sourced from local quarries. Homes built in the 1980s are the most affected, but older and newer properties may also be at risk.
How to Test for Pyrite
A standard home inspection doesn’t include pyrite testing. Instead, a laboratory test must be done to analyze the backfill and concrete slab. The Swelling Potential Petrographic Index (SPPI/IPPG) is used to rate the risk level. The average test costs around $850, and it’s typically the seller who covers it.
What If Pyrite Is Found?
If pyrite is confirmed, the only permanent fix is to:
- Remove the concrete slab
- Excavate and dispose of the contaminated backfill
- Pour a new slab using certified, non-swelling backfill (DB Certified Rocks)
This is a costly process, often taking several weeks, and prices vary depending on the size and severity of the damage.
Legal and Real Estate Considerations
In Quebec, pyrite can be considered a hidden defect—but only if it caused damage before the sale and was unknown to the buyer. That’s why disclosure and proper testing are essential.
Real estate brokers in Quebec are required to inform clients of pyrite risks and recommend testing. If pyrite is found, they may advise adjusting the selling price or including an expert clause in the promise to purchase.
