Pyrite damage is caused when the hardcore material (stone under the concrete slab) swells causing subsequent upward and sideways expansion which “lifts” internal walls, floors, causes doors to stick and cracks to develop.

The process which causes the swelling is a chemical reaction however can be summarised as follows:

1. Pyrite containing hardcore material is placed under your ground floor concrete slab
2. When the hardcore is subjected to oxygen and moisture it oxidizes causing sulphuric acid to be produced.
3. The acid reacts with limestone found in the hardcore.
4. The chemical reaction forms gypsum within the stone layers which causes swelling under huge pressures.
5. These pressures lift the concrete slab, internal partitions, pushes out walls etc causing cracking and other damage.

If you are experiencing sticking doors, persistent opening of cracks and new cracking, lifting floors etc the first thing to do is to assess the damage to determine if it is consistent with pyrites. This is done visually in the first instance and if the damage is consistent with pyrites then the next step is to take a physical sample of the hardcore which involves coring a hole through the floor slab and removing 15kg of stone for chemical analysis.

Once the presence of pyrites, or not, is established the process of entire removal will begin. There is no simple solution except entire removal of the ground floor and hardcore back to soil and then reinstating the floor, internal walls, kitchens etc. This process will take between 9 – 12 weeks.

At Building Surveying Solutions we provide the initial inspections and a reasonable cost and if our findings suggest the possibility of pyrites Golder Associates will undertake the sampling.

Depending on the age of the property, if the original building contractor is still solvent, if the property is under warranty etc the costs of the works may be covered or the costs may be borne by the house holder. We can advise on the likely hood of successful pursuit of the contractor or whether legal advise should be sought.

Should you wish to speak to a building surveyor about this further please contact us on (01) 884 7928 for further information.