House problems · Pyrite · IPPG test and sale
On the South Shore, the buyer of a 1992 bungalow asks for the pyrite test before the radon test. Here is what the IPPG measures, where the risk is, what a slab costs, and how it is settled between seller and buyer.
Pyrite is a mineral found in some crushed stone used as backfill under basement and garage slabs, mainly on the South Shore and in southwest Montreal between the mid-1980s and 2000. Oxidizing on contact with moisture, it swells and heaves the slab: star cracks, domed floor, partition walls pulling away from the ceiling. The test, under the CTQ-M200 protocol, cores the slab, samples the backfill and measures the petrographic index of swelling potential (IPPG): the higher it is, the greater the risk; count $500 to $1,500. Replacing the backfill and slab of a basement runs from $15,000 to $40,000 on the 2026 market, more with a garage. Pyrite does not affect the foundations themselves, unlike the pyrrhotite in concrete in the Mauricie, whose SHQ aid program has been suspended since April 1, 2025. At the sale, a recent test or a past replacement warranty is disclosed and shown; at purchase, the test is a common condition on the South Shore.
Pyrite (iron sulphide) is present in some shales quarried in the Montreal region. Crushed into backfill under the concrete slab of the basement or garage, it slowly oxidizes on contact with air and moisture, produces gypsum that takes more room, and lifts the slab from below. Symptoms take ten to twenty years to appear: star or map cracks in the slab, floor doming in the middle of rooms, basement partitions pulling away from the ceiling, white powder in the cracks, doors that stick. The foundations (the walls) are not affected: it is a slab and backfill problem, which distinguishes it from pyrrhotite, which attacks foundation concrete in the Mauricie and Centre-du-Québec.
Houses built between the mid-1980s and the early 2000s in sectors supplied by the quarries concerned: South Shore (Brossard, Longueuil and Saint-Hubert, Saint-Lambert, La Prairie, Candiac, Sainte-Catherine, Saint-Constant, Delson, Châteauguay), southwest of the island (LaSalle, Lachine, Pierrefonds, Dollard), and parts of Laval and the North Shore. After 2000, the backfill standard (DB-certified stone, with no swelling potential) solved the problem for new builds. A 1995 bungalow in Brossard with an intact slab may have no problem at all: the only way to know is the test.
An accredited lab cores the slab in two or three spots, samples the backfill, analyzes its composition and calculates the petrographic index of swelling potential (IPPG), a score expressing the share of at-risk particles and their state of oxidation. The Régie du bâtiment classifies quarries by this index: the lower the IPPG, the less the backfill is likely to swell; high-index backfills are the ones that caused damage. The report also states backfill thickness and whether swelling is under way. Count $500 to $1,500 depending on the number of cores and the lab (2026 market), and one to three weeks. A test under ten years old with a low IPPG is a document buyers generally accept.
When the backfill swells, the only lasting repair is to break the slab, remove the backfill (often 30 to 60 cm), replace it with certified stone and pour a new slab, with under-slab plumbing, the floor drain and sometimes the French drain redone. The 2026 market puts a bungalow basement between $15,000 and $40,000, with an attached garage extra. A repair done with an invoice and a DB stone certificate sells as an asset; a slab "repaired" by resurfacing solves nothing and shows in the test.
The seller discloses what they know: test done, results, work done, claims. A replaced slab with documents reassures; a low-IPPG test reassures; no test in an at-risk sector generally costs a 10 to 15 day offer condition and, if the result is bad, a renegotiation around the cost of the work. The buyer requires the test as a condition, reads the report with the inspector and, in case of a high index without symptoms, weighs a credit against a warranty clause. Some title insurance and new-home warranties (GCR) covered pyrite for limited periods; recourse against quarries and contractors is mostly time-barred. Our pages buying a house in Brossard and living in Brossard flag the sectors where the test is the norm.
The lab report interprets it: low-index backfills are considered low swelling potential, high indexes at risk. Read the report's conclusion rather than the number alone, because the state of oxidation and the backfill thickness matter.
Yes, when it causes damage not apparent at the time of the sale and a prudent buyer could not detect it; a test or a seller's disclosure changes the analysis. A buyer who waived the test in an at-risk sector will have a harder time complaining.
Not for pyrite. The SHQ aid program targeted pyrrhotite (foundation concrete in the Mauricie) and has been suspended since April 1, 2025.
Very rarely: since the early 2000s, backfills certified free of swelling potential are the norm; the risk mainly concerns 1985-2000.
These problems are easier to settle before listing than after the buyer's inspection: see the pre-purchase inspection in Quebec, latent defects in Quebec and renovating before selling.
The Loaa & Manseur team, led by Lotfi Manseur and Loaa Al Daow, is the number 1 team at RE/MAX Platine in 2024 and 2025, 6th RE/MAX team in Quebec, 15th in Canada and in the global top 50 of large residential teams according to the official RE/MAX ranking, computed on actual transactions. Its Google profile counts 221 reviews with a 4.9 rating. Its offices are at 55 avenue de l'Équinoxe in Brossard, one bridge from the island, and every broker's licence can be checked in the OACIQ public register. Three things to verify yourself before calling us, and to demand of any other broker.
Also available in French: version française de ce guide.
Published September 7, 2026 by the Loaa & Manseur team, the number 1 team at RE/MAX Platine in 2024 and 2025, 6th RE/MAX team in Quebec, 15th in Canada and in the global top 50 according to the official RE/MAX ranking. Tell us about your project.
Quebec runs on civil law, so several French terms have no direct English equivalent: hypothèque is a hypothec and not a mortgage, vices cachés are latent defects, and the taxe de bienvenue is legally transfer duties. The full list is in our Quebec real estate glossary. See also this term explained.
Équipe no 1 de RE/MAX Platine en 2024 et en 2025, 6e au Québec, 15e au Canada et dans le top 50 mondial au classement officiel RE/MAX. Réponse en moins de 24 heures, sept jours sur sept.