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The Painted House

With greater public awareness of the problems of swelling attributable to
pyritic backfill, the phenomenon has raised anxiety bordering on panic among
owners of buildings in the most affected sectors. And the same applies to the
real estate market.

The pyrite problem raises a lot of questions— scientific, technical, and legal.
Since the fall of 1998, agencies have received thousands of calls from
citizens concerned by some aspect of the problem, especially on the South Shore of Montréal.

Numerous cases of garage and basement concrete slab distress at various
levels of heaving and deterioration were noticed early after construction in the
Montreal south-shore area . The use of clayey sedimentary rock containing
pyrite as aggregates for granular subbase is responsible for most of the
observed distress. The heaving of the slabs is related to the oxidation process
of the pyrite, followed by sulphate crystallization causing the swelling of the
compacted granular subbase. A first inspection survey was carried out in the
summer of 1999 in an attempt to assess the extent and magnitude of the
damage caused by pyritic rockfills. More than 200 houses showing distress
associated with pyrite were investigated in three localities. Damage of the
garage floor slab seems to occur earlier after construction and to be more
severe likely due to the subbase thickness and to the lower quality of the
rockfill. Five houses at various stages of reaction process were monitored.
The results suggest that the rockfill swelling is quite fast and continuous

Removing pyrite can be very costly. It is important to verify for the existence
of pyrite. We do not test for pyrite.