Buying a House in a Mica County: Defective Concrete Blocks and the Scheme

Thousands of Irish homes were built with concrete blocks that crumble as they weather. In the counties the State scheme covers, the question is not whether the problem exists but whether this house has it — and the answer costs the seller a test, not you a mortgage.

What went wrong, and where

From the 1990s, some block manufacturers supplied concrete blocks containing excessive mica or pyrite. Over years the blocks absorb water, swell, crack and lose strength; walls craze, render falls away and, in the worst cases, houses have to be demolished and rebuilt. The problem is concentrated where the affected quarries supplied: Donegal and Mayo first, then Clare, Limerick and Sligo were added to the Government’s Defective Concrete Blocks grant scheme.

The enhanced scheme grants up to €420,000 towards remediation, with the work graded from re-rendering to full demolition and rebuild depending on the damage. Being a scheme county does not mean every house is affected — it means a house of the right age there deserves the question.

What to ask for before you bid

The test is a core sample of the blockwork analysed under the national standard, I.S. 465, by an engineer. In scheme counties, a seller of a 1990s-to-2010s house should expect the question, and a clean report is a selling point. A surveyor will also look for the tell-tale signs — map cracking, cracks radiating from window corners, render blowing off at ground level.

A house already approved under the scheme can be bought, but the grant and the works have rules: check which remediation option was approved, whether the grant transfers, and what has actually been done. Your solicitor needs the paperwork, not the story.

Beyond the five counties

Blocks were sold across county lines, and defective blocks have been reported in homes outside the scheme area; proposals to extend the scheme have been debated more than once. The county flag is where the problem is established and where the State has stepped in — it is not a promise that a house just over the border is sound. The age of the house and the look of its walls apply anywhere.

Pyrite in hardcore under floors is a separate, older problem, concentrated in the Dublin, Meath, Kildare and Offaly commuter belt and handled under its own remediation scheme. Heaving floors, cracked tiles and doors that no longer close are its signature, and the same rule applies: ask whether the house has been tested and remediated, and read the certificates.

How a VeriSale report grades it

VeriSale resolves which county the property sits in and checks it against the counties the Defective Concrete Blocks scheme currently covers.

• Scheme county (Donegal, Mayo, Clare, Limerick, Sligo)Flagged mid, with the ask: “ask whether the home has been block-tested before committing.”
• Not a scheme countyGraded well — a county-level flag, not a statement about the house.

This is one of 39 checks in the report, each graded A–F with a plain-language summary. The report compiles public data; it is not a survey or legal advice.

What to ask before you bid

• When was the house built, and who supplied the blocks?
• Has the house been tested to I.S. 465, and can the seller provide the engineer’s report?
• Has the house been accepted onto the Defective Concrete Blocks scheme, under which option, and what works have been completed?

Frequently asked questions

Where this matters most

County guides that single out defective blocks (mica) as a check to read closely:

Other checks explained