Defective concrete blocks in Donegal ‘not caused by mica’, study claims

Research published in leading international journal suggests issue has been caused by pyrrhotite

Defective concrete blocks in homes in Co Donegal are failing because of pyrrhotite and not mica, according to a study published in leading international journal Cement and Concrete Research.

There could be 2,000 legal actions, with a total value of €550 million, concerning mica-affected concrete blocks before the end of the year, it has been claimed in High Court proceedings. Some 1,100 cases have already been issued.

They are suing over damage from concrete blocks and similar products containing mica that were used to build their home between 2005 and 2008. Mica is naturally occurring in rocks but, when used as an aggregate, makes concrete weaker over time.

However, a study conducted by researchers at Empa, Switzerland, Ulster University, UK, and the TA Group suggests that defective concrete blocks in Donegal are failing because of pyrrhotite and not mica.


The peer-reviewed article entitled The Mica Crisis in Donegal, Ireland – A Case of Internal Sulfate Attack “confirms that the geological mineral mica is not the primary cause of failure of defective concrete blocks in Donegal homes”.

It instead suggests it “is the mineral pyrrhotite present in the aggregate found in defective blocks”.

The mica diagnosis was proposed by a government report published in 2017 and incorporated into the National Standards Authority of Ireland (NSAI) testing and remediation standard.

Ulster University’s Prof Paul Dunlop, one of the authors of the research, said: “This new scientific evidence is important for the for Government officials and policy makers who are dealing with the defective concrete block crisis to ensure science based solutions are at the heart of government solutions for affected homeowners.

“Its publication is also timely for the NSAI who have been calling for rigorous, independently peer reviewed scientific data for their ongoing review.

“In addition, it provides scientific information for the National Building Control and Market Surveillance Office who are tasked with market surveillance about the obvious risks for concrete failure when aggregates containing pyrrhotite are used and reinforces the need for robust surveillance of the extraction industry and concrete manufacturers.”

The researchers say they have uncovered “robust scientific evidence” and accurately accounts for the phenomenon of concrete failure manifested in Donegal homes build from defective concrete blocks.

“The paper uses rigorous scientific methodologies to investigate and describe this failure mechanism for the first time in detail and outlines why mica cannot be the cause of concrete block failure in Donegal homes,” they add.

The Department of Housing has been contacted for comment.

Colin Gleeson

Colin Gleeson

Colin Gleeson is an Irish Times reporter