What To Do If You Find Pyrite in Your Home’s Foundations

When iron pyrite deposits were discovered in Quebec, the first settlers to arrive in New France thought they had found a source of wealth. Unfortunately for them, this “fool's gold” was of little value.

Today, in certain situations, pyrite can be considered a contaminant, notably when it is present in the backfill used for building construction.

But does pyrite-contaminated soil represent a real danger? And if so, how do you get rid of it? Our experts in contaminated soil remediation explain.

What is iron pyrite?

Pyrite is an iron sulphide mineral of the sedimentary rock family. It occurs naturally in several types of rock formations, particularly in Quebec and the northeastern United States. 

Iron pyrite has a slightly golden colour, a bright metallic luster and it is opaque. It tends to crystallize, so its surface reflects light like gold. Its appearance therefore contributed to early settlers confusing pyrite with real gold. However, around the year 50, the Greeks were already using it as a fire stone, hence the name pyrite from the Greek "pyros"

Is pyrite dangerous for your health?

In contact with oxygen, water and humidity, pyrite oxidizes and produces sulphuric acid. The phenomenon of pyrite oxidation also leads to the formation of gypsum crystals, which increases its volume.

Unlike asbestos and lead which can be harmful to human health, pyrite is not considered a hazardous material by law. On the other hand, it can cause other types of significant problems, especially when it is present in the backfill material used under the slab of a building.

How to tell if your home contains pyrite

Performing a pyrite test

Problems associated with pyrite-contaminated backfill

Before pouring a concrete slab, it's common practice to spread crushed stone (backfill) to level the surface. However, due to the chemical properties of pyrite, backfill containing this mineral can create a number of problems.

Fill swelling

When in contact with iron pyrite, the backfill could swell and cause cracking of the basement and garage floor slabs. Damage may also occur to the foundation walls.

This process is quite slow and is sometimes only noticeable 10 years after the building was constructed. In fact, many homeowners may become aware that their residential property is contaminated when star or cross-shaped cracks appear on their concrete floors from which fine gypsum dust emerges.

Cracks in the backfill

In a finished basement, since cracks and damage to the concrete are concealed by the building materials, it is even more difficult to detect a pyrite problem in the backfill. 

However, the danger is still there. Cracks in the slab can allow moisture from the soil to penetrate your home, promoting mold growth and the degradation of floor coverings. In extreme cases, swelling and cracking can even weaken the load-bearing elements of the building. 

A house’s market value will therefore decrease considerably if pyrite problems have been detected and confirmed by a pyrite test. 

What to do after a positive pyrite test ?

Pyrite problems can be solved with a lot of effort, time and resources. For basements or converted garages, it may be especially difficult.

If you're wondering how much it costs to remove pyrite, there are several factors to consider. First, the concrete slab covering the pyrite-contaminated backfill must be broken up, and all contaminated soil removed. Next, it must be replaced by DB crushed stone (DB certification indicates it is non-swelling) before pouring a new concrete slab. 

Removing pyrite from a garage usually costs several thousand dollars. If access to the basement or garage is difficult, costs may rise accordingly. To find out more about rates, contact a specialist.

For all your contaminated soil problems, contact EBI Enviro Urgence

Pyrite-contaminated soils are a nuisance. The longer you wait, the more iron pyrite can grow and cause significant damage to your property. The structure of the house could even be affected, depending on its construction.

Other than property damage, pyrite poses no major health risk to you or the people in your home.

If you ever have questions related to the management of hazardous materials that you do not know how dangerous they are, contact our specialists! They will be able to enlighten you and propose environmentally friendly decontamination solutions.