Pyrite in Residential Property-What You Need to Know to Avoid a Catastrophic Problem


Pyrite in your property has the potential to break your heart and cause you catastrophic loss.

What is pyrite?

I’m not an engineer but my research has discovered that it is a common mineral that occurs in rocks.

In particular circumstances a chemical reaction, which creates expanding crystals within the material, can occur which causes the pyrite to swell causing the construction material in which the pyrite is present to expand, heave, crack and eventually crumble.

This problem occurs mostly in the floors of houses causing huge problems for the property owner rendering the home virtually unsalable until the problem is resolved.

Indications of Pyrite Damage

Some tell tale signs include:

  • Lifting of the floor slab resulting in cracking
  • Cracking of floor finishes and tiles
  • Doors catching on floors
  • Horizontal cracking externally at damp proof course level
  • Cracking on internal walls over doors
  • Cracking of ground floor stud partitions and cracking of plasterboards.

Most, but by no means all, of the houses in Ireland where you will find problems with pyrite are located in North Leinster and the Greater Dublin area including Meath, Offaly and Kildare.  The reason for this is the use of stone from quarries in this area which contain framboidal pyrite.

IS 398 published by the NSAI in 2013 aims to set new standards in relation to pyrite by providing protocols for testing and categorisation and setting out a methodology for remediation works.

IS 398 provides for 3 certificates in relation to the presence or absence of pyrite in the underfloor hardcore of a house:

  1. Green means it is pyrite free
  2. Amber means the hardcore is susceptible to limited or significant expansion and monitoring of the damage is required
  3. Red means you have a pyrite problem and the stone infill in the floor of the house will have to be removed and replaced. This involves the removal of the floor slab, insulation and damp proof membrane. The replacement stone and remedial works should also be certified in accordance with IS 398.

Buying Your New Home

When buying  a house you should make sure to have a structural survey carried out first. Then, your engineer should be able to advise you whether further investigation is necessary to ascertain the position in relation to pyrite.

You may have to insist that you are provided with a report from an accredited laboratory confirming that the property is pyrite free before proceeding with your purchase, especially if the house is in one of the areas where pyrite is a problem.

This will involve the taking of core samples from the floor of the house and a delay of about 3 or 4 weeks as much of the testing is carried out in laboratories in the UK. But it is strongly advisable if your engineer tells you that further investigation is necessary.

If in any doubt, discuss this with both your engineer and solicitor because the consequences of buying a property with a pyrite problem are very serious.