Pyrrhotite Foundations in Trois-Rivières: Recognizing the Cracks, Testing the Concrete and Replacing the Foundation

Recognizing pyrrhotite damage

Pyrrhotite damage does not look like ordinary settlement cracking. It starts as fine map-pattern or crazing cracks across the foundation walls, inside and out, that widen year by year; the walls bulge outward and the concrete at the surface becomes friable; white or rust-coloured deposits appear along the cracks; and in a finished basement the drywall cracks and the floor slab heaves. Ordinary shrinkage cracks are single, vertical and stable. The damage appears years after the pour, typically ten to fifteen, which is why it kept surfacing long after the quarry stopped supplying.

If the house was built in the Mauricie between the mid-1990s and 2008, assume it is possible until a test says otherwise. Sellers in Quebec must disclose known pyrrhotite, and buyers routinely make an offer conditional on a test.

Testing and what the result means

The test is a core sample drilled from the foundation wall and analysed by a qualified laboratory for pyrrhotite content, expressed as a percentage of the aggregate; the courts and the programs have used thresholds to decide whether a foundation is considered affected and must be replaced, and the current program terms state them. A test costs a fraction of a replacement and is the only way to know; a visual inspection cannot rule pyrrhotite out. Keep the lab report; it is the document the program, an insurer, a buyer and a court will ask for.

The Coalition d’aide aux victimes de la pyrrhotite, based in Trois-Rivières, has guided owners through testing, the programs and the litigation for more than a decade and is the first call for anyone who suspects a problem.

• Year the foundation was poured and, if known, the concrete supplier
• Photos of the cracking pattern, inside and out
• Core test ordered from a qualified lab
• Lab report kept with the house documents
• Program eligibility checked with the current terms

What a replacement involves

A foundation replacement is the largest job a house can have short of demolition. The house is lifted on cribbing and steel beams, the old foundation and slab are demolished and hauled away, a new foundation is poured with certified aggregate, the house is lowered and reconnected to its services, and the basement is rebuilt; the family lives elsewhere for weeks. The work needs a structural engineer’s design, a City of Trois-Rivières permit, and an RBQ-licensed contractor with experience in lifting houses, of which the Mauricie now has several. Get the engineer’s design first and the contractor quotes against it.

Programs, liability and who to hire

The Quebec government, with federal contributions, has funded a program administered through the Société d’habitation du Québec and the City that has covered a large share of the replacement cost for eligible owners, with conditions on the test result, the property and the contractor; the terms and the funding have changed several times, so check the current program before planning anything. The court rulings against the quarry, the concrete suppliers and the geologist established liability for many homes built in the affected years, and owners of some homes have recovered through those judgments. Hire an RBQ-licensed contractor with pyrrhotite replacements to show you, a structural engineer registered with the Ordre des ingénieurs du Québec, and keep every document.