The Dreaded “P” Word in Montreal Real Estate: Pyrite

You’ve found the perfect home for you and your family. You and the seller have come to an agreement on price.  And as a responsible home buyer, you get the property inspected.  While in the garage, and then in the basement, the inspector says, “Hmmmm, those cracks in the floor may be due to pyrite. Better get it tested to know for sure.”

At this point, you and the seller of the home will likely have one of two reactions:

“Pyrite?  What the heck is pyrite?”


“OMG, pyrite?!  My world has come to an end.”

What is pyrite?

Pyrite is a natural mineral.  Traces of it are found in the rock used to make crushed stone which is used for backfill in construction.  Backfill is used under the concrete slab in the building of garages and basements.

What’s the problem?

Pyrite oxidizes when it comes into contact with air (oxygen) and moisture (humidity).  Through a series of chemical reactions under certain conditions, some of the crushed stone used in the backfill can burst.  When the backfill contains enough rocks that are reactive to pyrite, this can lead to the backfill swelling and to the concrete itself crumbling, swelling and/or cracking.  Interior partitions resting on the slab may also heave, which may in turn damage upper floors and partitions.

The swelling is usually worse in garages, where a thicker layer of backfill is used and the stones used in the backfill are compacted so that there is very little give between them.

How bad is it?

The potential damage caused by pyrite varies from case to case.  In some cases, it is severe, where door jams on upper floors come away from the walls, interior walls develop huge cracks, and the swelling or heaving of the concrete slab can be 6 inches (15 cm) high.

In other cases, a homeowner can have absolutely no idea there is anything unusual going on, because any damage caused by the pyrite in their home seems like regular wear and tear.

How quickly does the damage show?

On average, it takes about 10 years to see any damage from pyrite.

How do I know if I have pyrite?

Standard testing procedure is now in place to test for the presence of pyrite.  I’ve used the company Pyritest before.  They follow the established protocol for testing (CTQ-M200) and will take samples of the backfill in the basement and the garage back to the lab for testing.

The results of the testing will produce what’s called the IPPG in French (or SPPI in English – pyrite swelling potential index).  This is NOT a pyrite percentage but rather an indication of the quality of the backfill material.  The IPPG ranges are as follows:

0 to 10: Negligible risk of damage foreseen due to swelling of the backfill

11 to 20: Low risk of damage foreseen

21 to 40: Low to moderate risk

41 to 60: Moderate to high risk

61 to 80: High risk

81 to 100: Very high risk

Once pyrite is detected in a home, we are under a legal obligation to disclose that fact to buyers.

What regions are affected?

It used to be that problems associated with pyrite were found only in Montreal’s Montérégie, particularly on the South Shore.  This is no longer the case, and we now see it in Montreal West Island homes (among other areas).

Are all homes affected?

No. Pyrite is not generally seen in new construction nor in very old homes.  Most cases occur in homes that were built from the late 1970s to about 1990. And it depends on the source of the backfill used.

And here’s the homework…

The West Island is my territory, and as such I want to keep you, Montreal West Island home buyers and sellers, well-informed.

I am not, however, a home inspector nor a general contractor, nor a geologist nor a lawyer. The key is to listen to your home inspector, follow-up with professional testing for pyrite if recommended by your home inspector, consider the test results and the geologist’s opinion, and discuss all of this with your real estate broker, whose sole purpose is to represent your best interests.