Pyrite (FeS2 Iron Sulphide) is a mineral that can be found in very small amounts in sedimentary type rock used to make crushed stone for backfill. Backfill is often placed under concrete floor slabs.

The presence of pyrite in the backfill can cause cracking in houses causing vertical heaving or upward pressure within the floor slabs and through the floor slabs at ground level resulting in the bulging and cracking of floors, partition walls and door frames.

These chemical reactions are usually a slow process; it may take up to ten years before damage occurs cases of pyritic damage have taken as little as three years to appear. In some cases in Dublin and Ireland signs of pyrite heave have appeared in less than a year after the dwelling was completed. It should be noted that the presence of pyrite alone does not directly lead to pyritic heave. It is the responsibility of the home owner to prove a case of pyrite heave.

Call 01 491 2415 today or email if you are concerned about potential pyrite problem in your property. We will provide you a quote for a visual building condition assessment with level survey and detailed report of findings.

What are the symptoms of pyrite heave?

  • 1. Lifting (heaving) of a ground bearing concrete slab causes star, cross or web shaped cracks spreading across the concrete slab. There is also an occurrence of small white crystals mixed with the concrete near the cracks.
  • 2. Bulging and cracking of floor tiles. Floor tiles sloping and cracking along its joints.
  • 3. Timber floors bulging and sloping. Timber floor joints opening up.
  • 4. Internal doors sticking and catching on the floor slab.
  • 5. Continual opening up of filled in cracks and new cracking.
  • 6. Cracking and bulging of internal partition walls.
  • 7. Cracking above windows if walls are internally drylined.
  • 8. Cracking at wall junctions.
  • 9. Horizontal cracking at ceiling wall junction.
  • 10. Cracking and bulging of wall tiles.
  • 11. Crack between external wall and slab at external door threshold. Top of floor slab projecting up above door threshold level.
  • 12. Kitchen worktop, cupboards and fitted wardrobe units separating from walls and/or becoming deformed due to the upward pressure from pyrite heave.
  • 13. Horizontal cracking at or near ground floor level in external walls with some lateral movement The above symptoms are indicative of pyrite heave but may also be associated with normal settlement or other problems ie subsidence.

The damage caused by pyrite heave is progressive in nature and as a result will become more exaggerated and visible over time.

What to do if I suspect I have a pyrite heave problem?

If you are experiencing the above symptoms you should engage competent structural engineer like PKT Consulting Engineers Ltd (Call: 01 491 2415 or Email: who has knowledge and experience of pyrite problems to carry out a detailed survey. If the cracking is caused by pyrite heave and all other possibilities of the cause of the cracking have been ruled out, then samples of the backfill (hardcore) should be taken. This involves coring a hole through the floor slab and removing the backfill for chemical analysis testing.

What type of repairs may need to be carried out?

Set out below is a brief summary of the steps required for carrying out repairs:

  • 1. Damage assessment and repair specification including program of works.
  • 2. Remove concrete floor slab, insulation and DPM to expose backfill. Temporary propping may be required for the upper floors.
  • 3. Remove all backfill aggregate so that pyrite heave will not occur again. Clean rising walls of contamination.
  • 4. New backfill material reinstated to current standards.
  • 5. New DPM and insulation placed on top of compacted backfill.
  • 6. New concrete slab poured.
  • 7. Remedial works carryout internally, all fixtures and fittings returned. Repainted and decorated.
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