A protest took place on Tuesday while the Dáil sat at Dublin’s Convention Centre calling 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.