Pyrite is a very common mineral found in rock used to make crushed stone for back-fill under concrete slabs in garages and basements. Pretty sexy eh? By itself pyrite is not normally an issue, but when combined with moisture and oxygen in a confined space it can potentially cause some big problems.
So what is the problem?
The presence of reactive pyrite in the back-fill can result in a section or the entire floor slab to lift and heave several centimeters, causing star-shaped cracks in the slab that are often accompanied by white mineral deposits. The greater the concentration of pyrite and thickness of back-fill, the higher the risk of structural damage to foundation walls.
Pyrite issues have been identified in 91 cities in the Greater Montreal area. As a homeowner, you should be aware that high-risk areas in the West Island include Lachine, Dorval, Dollard-des-Ormeaux, Pointe-Claire, Kirkland, Pierrefonds-Roxboro, and Beaconsfield.
Most concrete floor slabs will develop curing and settlement cracks. This is normal. As concrete dries, it shrinks. These long, thin cracks are most likely not caused by swelling due to the presence of pyrite.
If your inspector suspects pyrite he or she will recommend a pyrite test be done by a laboratory. A sample will be collected from under the concrete slab and a report will be issued, detailing the potential for swelling of the backfill found in your home. The pyrite swelling potential index ranges from 0-100.
0- 20 is generally considered minor and non-problematic.
20-40 is considered moderate and may be problematic depending on a few factors.
40-100 is considered high and will most likely need to be removed in order for a lender to grant a loan for the purchase of the property.
You can visit our YouTube channel to watch a video showing how a sample is collected.
Do you have any questions about pyrite or any other issues that could affect the value of your home? Would you like to know what your home is worth in today's market? How about some advice on which updates, renovations, or repairs would have the biggest impact on your resale value?
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