Q&A: What is mica and why are people protesting over it?

Mineral found in rocks used in building blocks has caused defects in properties

A protest is due to take place while the Dáil sits at Dublin’s Convention Centre on Tuesday amid calls for a mica redress scheme for thousands of homeowners in the northwest. What is the controversy about?

What is mica?

Micas are types of minerals found in the ground and in rocks excavated in quarries. Muscovite, biotite and phlogopite are the three most common mica group minerals found in rocks, and consequently in building blocks.

And what is the issue with this mica?

Muscovite mica has led to apparent defects in building blocks used in at least 5,000 homes in the northwest, causing cracks to open up in thousands of buildings. Videos posted online show load-bearing blocks crumbling in homeowners’ hands.

How does this happen?

From experiences recounted by the Mica Action Group and the Report of the Expert Panel on Concrete Blocks published in 2017, it seems mica attracts moisture from the environment, with external walls in some cases absorbing moisture from the ground like a sponge. The presence of mica affects the strength of the blocks and they eventually crumble, seemingly after about five years.


Why are only some blocks affected?

External walls are most exposed to the elements, internal walls are better protected, but not immune to problems.

Is this the same as pyrite, which caused

problems with homes in Leinster?

For practical purposes it is similar. Pyrite or Iron pyrite (FeS2) is a common mineral found in sedimentary and low grade metamorphic rocks.

What does an affected house look like?

Walls get web-like cracking, crumbling blocks and plaster cracks, which in the early days looks like minor subsidence or “settling”. But over time many homes have vertical cracks close to the corners that extend from ground to roof.

How can this happen?

Statutory Instrument number 288 of 1949 set a 1 per cent at total limit for impurities such as pyrite and mica in concrete blocks. The Expert Panel on Concrete Blocks consulted the National Standards Authority on this for its 2017 report to government. The clear view of the authority – and expert panel – was that the 1 per cent limit still applies.

And that was breached?

An impurity/mica level in the region of 17 per cent has been found in blocks in a number of the affected houses in Co Donegal.

Who polices this and has the testing or inspection regime on building supplies changed since these problems emerged?

The Department of Housing said since 2013, on foot of an EU regulation, there is “a suite of harmonised standards covering most construction products including aggregates, and concrete blocks”. This is called the the Construction Products Regulation.

However the department said: “It should be noted that primary responsibility for demonstrating a construction product’s compliance with the requirements of the Construction Products Regulation rests with the manufacturer of the product.”

What about builders’ insurance?

The Construction Industry Federation (CIF), through HomeBond Insurance Services, offers an insurance policy for home builders. These offer protection for problems such as “latent defects” and “ structural issues” among others. It is not known how many, if any, of the builders of the affected homes had taken out such policies. Questions were put to the CIF on Monday and a reply is expected.

But it is a moot point according to campaigners as many of the homes were one-off, self-build housing, with the number of “estate houses” thought to be small.

So are we looking at just a few one-off houses in the north west?

Not exactly. The numbers reported recently have been in the order of 5,000 homes in Donegal and Mayo. But there are more reports of homes in Clare, Sligo and Northern Ireland being affected. The final figure could be closer to 10,000 houses.

But are we just talking houses?

The Mica Action Group campaigners claim building blocks from the same supplier were used in public projects over many years. A spokeswoman said the fear was that these blocks may be in shops, schools and even hospitals.

What will it cost to repair?

The last government announced a scheme before the 2020 election to support householders affected and pay for 90 per cent of renovation costs. Recent reports citing Government sources have mentioned a figure of some €1 billion.

What is the Government doing?

Tánaiste Leo Varadkar said the Government was “keen to find a solution” to the issue. Minister for Housing Darragh O’Brien said he and his department have been working through submissions from the action group “which we received five weeks ago and we are liaising with other departments and agencies to figure out how best to address some of the concerns raised”.

How was the pyrite problem resolved and is the mica redress scheme different?

The pyrite problems were resolved after homeowners were granted 100 per cent of the costs involved in repairing their properties. The current Defective Concrete Blocks Grant Scheme was introduced last year and covers 90 per cent of rebuild costs, but there are snags.

Homeowners must pay for tests, sampling and certification which can cost up to €5,000. There are exclusions including windows and kitchens and for demolition and rebuild planning and architect fees are not covered. The scheme provides for repair costs from €50,000 for a partial rebuild to a maximum of €275,000 for demolition and a complete rebuild.

Many of those affected claim this is not enough. The scheme opened for applications last June and so far less than 500 people in Donegal have started the process. Many of those disaffected will make their feelings known when they march in Dublin on Tuesday.

Tim O'Brien

Tim O'Brien

Tim O'Brien is an Irish Times journalist