News > In focus: Pyrite and Mica

In focus: Pyrite and Mica


In Ireland, there is a serious problem regarding the materials used on residential and commercial buildings. Having worked on a project dealing with this, our assistant building surveyor Christopher Williams was perfect to help us understand more about this issue…


Pyrite, also known as Iron Sulphate (FeS¬2), is a naturally occurring mineral that is commonly found in sedimentary or carbonaceous rocks. For a period in the 2000’s in Ireland, rocks containing pyrite were used for sub flooring material in buildings. Where some forms of pyrite are exposed to moisture and oxygen, a series of chemical reactions can occur within the rock, leading to oxidisation, which then forms sulfuric acid and other products. The acid then reacts with other minerals in the rock if there is calcium carbonate present, it will react with the sulfuric acid and create gypsum. Gypsum has a significantly greater volume than the source pyrite and the growth of its crystals, and will prise open cracks causing further expansion, including the cracking concrete slabs internal partitions and external walls, and/or warping of doorframes.


Mica is a mineral that is found in rock, often taken from quarries. The rocks from these quarries were used in construction before it was known to cause problems in buildings. Their main use was for hardcore or concrete blocks for walls however, Mica can absorb and store water in high quantities so defective blocks that contain high levels of Mica absorb water and cause cracking to external and internal walls, posing a major health and safety risk.

Some of the symptoms of Mica are listed below:

  • Vertical cracks at corners of the building
  • Cracks primarily affect the outer leaf
  • De-bonding of external render
  • Extensive cracking in exposed parts of chimneys
  • Horizontal displacement at window & door opening reveals
  • Cracking typically more prevalent on more exposed elevations

There are similarities between the two. The way in which these minerals impact concrete construction can be a serious issue in terms of structural integrity and in a building’s appearance.

Trident’s Dublin team is overseeing a remedial project for an industrial estate in Dublin where pyrite is having an impact on some of the units. This has led to the floors in a couple of the units lifting in areas and needing to be replaced. To permanently eliminate pyrite, all the contaminated backfill under the concrete slab must be replaced. The work primarily consists of clearing the entire area across the concrete slab, breaking and removing the concrete slab currently installed, removing all the backfill and replacing it with new certified crushed stone.

In Ireland, a green certificate is awarded to a property that has been formally tested and deemed pyrite free. The certificate will be completed and signed by the chartered structural engineer and by the contractor who undertook the works shows how the pyrite was removed from some of the units.

If you are experiencing issues with your properties that may benefit from surveying, please get in touch with Christopher on 0830984179 or at