IS465 – AOCA Experts in Pyrite/Mica

Pyrite/Mica in block-work has, and is, causing serious damage to numerous properties all over the country, with most of them in the North West.  Due to the extent of the problem, the NSAI set up an expert committee to produce a standard to deal with it.  Aidan O’Connell, a Fellow of Engineers Ireland and Managing Director of AOCA Engineering Consultants, and Colin Scott, a Chartered Engineer, MSc. LLM C.Eng, MIEI, AMI StructE, MICE, MCIArb and Associate Director of AOCA Engineering Consultants, were both asked to sit on an expert committee and were heavily involved in the compilation of the new standard IS465.

The Expert Panel was of the opinion that: “the reason for the widespread pattern cracking in private dwellings in Counties Donegal and Mayo is primarily due to the excessive amount of deleterious materials in the aggregate used to manufacture the concrete blocks.  The deleterious material in County Donegal was primarily muscovite mica, while in County Mayo it was primarily reactive pyrite.”

Concrete blocks manufactured from aggregates containing certain potentially deleterious materials, and subject to substantial ingress of moisture and or freeze thaw conditions, can have reduced strength and durability, resulting in disintegration.  Concrete masonry which remains in a dry state will not suffer from freeze thaw effect.

Click on the Link to view the full standard.

While the primary locations of the problem have been identified as Donegal and Mayo, AOCA has been involved in cases in numerous other counties including ones in the South West and South East. It is clear therefore that the problem is a national one rather than a regional one.

AOCA are perfectly situated in the centre of the country to service the entire island – and we would be more than happy to assist you in any queries that you may have in relation to this issue.


Aidan O’Connell        –           057 8663244 or via email at

Colin Scott                  –           01 4243035 or via email at