Mica Homes Ireland: Counties Affected, Warning Signs, and What Buyers Must Check

Buying a property in Ireland that turns out to have defective concrete blocks is not a minor inconvenience. It can mean a house that is structurally unsound, uninsurable, unable to be sold, and requiring complete demolition and rebuilding. The Enhanced Defective Concrete Blocks Grant Scheme covers remediation up to €462,000 — but affected homeowners still face funding gaps, years of disruption, and in some cases the discovery that insurance and warranties explicitly exclude these defects.

If you're buying a property in an at-risk county and it was built between 2000 and 2010, you need to understand this before you sign anything.

Two Separate Problems: Mica and Pyrite

Ireland has two distinct concrete defect crises, affecting different regions and caused by different minerals.

Defective concrete blocks (mica/pyrrhotite): Affects the west and northwest of Ireland. The primary counties are Donegal, Mayo, Clare, Sligo, and parts of Limerick. Some properties in Cork and Kerry have also been identified.

Pyritic heave: Affects the east of Ireland. Primary counties are Dublin, Fingal, Meath, Kildare, and Wicklow.

They have different causes, different visual symptoms, and different remediation approaches — though both originated in the construction boom of the early 2000s when building materials were not subject to adequate quality control.

Defective Concrete Blocks: The Mica Problem

Muscovite mica is a soft, sheet-like mineral. When present in aggregate used to manufacture concrete blocks, it absorbs moisture and disrupts the concrete's internal bonding. During winter freeze-thaw cycles, the absorbed water expands, further degrading the block structure from the inside.

The statutory limit for muscovite mica content in concrete blocks is 1%. In affected homes in Donegal and Mayo, mica concentrations of up to 17% have been found — far beyond anything the blocks were designed to accommodate.

In Mayo and parts of Sligo, the primary cause of block failure is slightly different: reactive pyrrhotite (a form of iron sulfide) rather than mica. Pyrrhotite oxidizes when exposed to moisture and oxygen, forming gypsum, which expands and causes internal cracking and spalling of the blocks.

The visual symptoms are similar regardless of whether it's mica or pyrrhotite:

• Stair-step or horizontal cracking along mortar joints in external rendered walls
• Spalling render — patches of the outer finish detaching in sheets
• External walls that look "bubbled" or irregular when viewed at an angle
• Internal cracks following mortar joints, typically visible at corners
• Damp patches inside walls despite no obvious roof or plumbing issue

A property in Donegal or Mayo that shows these signs needs a building condition assessment from a chartered engineer before you sign any contracts. The assessment costs €500 to €750 — refundable if the local authority validates the application to the Enhanced Defective Concrete Blocks Grant Scheme, but not refundable if the result is negative.

Full core testing and laboratory analysis of blockwork from suspected properties can cost up to €5,000. This is not optional for any serious purchase in an affected county.

Pyritic Heave: The East of Ireland Problem

In Dublin, Meath, Kildare, and Wicklow, the defect is in the sub-floor hardcore — the crushed stone aggregate used beneath ground floor concrete slabs during construction. If that aggregate contained reactive iron pyrite, it oxidizes over time when exposed to moisture and oxygen, forming gypsum.

Gypsum has a larger molecular volume than pyrite. This chemical expansion causes the sub-floor to swell — creating "heave" — which pushes upward on the concrete floor slab with enormous force. The result is:

• Cracking of internal walls in a distinctive spiderweb pattern
• Floors that slope or feel uneven underfoot
• Doors and windows that stick or no longer close properly
• Gaps appearing between skirting boards and the floor
• Cracks running from the corners of internal door frames

Standard home insurance policies do not cover pyritic heave. The HomeBond structural warranty — which covers new builds for ten years — also typically excludes pyritic heave. Buying an affected property without knowing its status can expose you to full remediation costs with no insurance or warranty coverage.

The Pyrite Green Certificate

When purchasing a second-hand property built between 2000 and 2013 in Dublin, Meath, Kildare, Fingal, or Wicklow, your solicitor should specifically request a Pyrite Green Certificate as part of the due diligence on the property.

A Pyrite Green Certificate confirms that the property's sub-floor aggregate has been laboratory-tested and declared pyritically inactive, or that full remediation has been completed under the Pyrite Remediation Scheme. Without this certificate, a structural survey alone cannot rule out the presence of reactive pyrite — the hardcore is beneath the concrete slab and cannot be visually inspected.

If no certificate exists, the next step is core testing. A core drill is made through the concrete floor slab to extract a hardcore sample, which is sent to a laboratory for analysis. This costs approximately €2,500.

The Pyrite Remediation Scheme: Deadline November 2026

The Pyrite Remediation Scheme, managed by the Pyrite Resolution Board, covers 100% of remediation costs for properties demonstrating significant pyritic damage. However, the scheme is entering its final wind-down phase. Applications must be received by 30 November 2026. After this date, no new applications will be accepted.

If you're purchasing a property in an at-risk area and the pyrite status is unknown, the timeline matters. A purchase that takes three to four months to close could leave you as the owner of a pyritic property after the application window has closed.

The Enhanced Defective Concrete Blocks Grant Scheme

For properties in the designated counties affected by defective blocks, the Enhanced Defective Concrete Blocks Grant Scheme provides:

• Up to €462,000 for full demolition and rebuild
• 100% of validated remediation costs within this cap
• A refundable building condition assessment (€500–€750) if the application is validated

The gap between the grant and actual remediation costs has widened. Grant rates were set based on construction costs from March 2024, and current market rates from building contractors have exceeded those benchmarks due to materials and labour inflation. Some homeowners face an unfunded gap even with the grant.

What to Do as a Buyer

Do not rely on the seller's representations. In Ireland, property is generally sold under caveat emptor — buyer beware. The vendor has no obligation to proactively disclose structural defects they're not legally required to disclose.

Always commission an independent structural survey. For any second-hand property in an at-risk county, this is non-negotiable. Brief the surveyor specifically to examine for mica or pyrite symptoms and to advise on whether further testing is warranted.

Check the structural survey findings against the property's location and construction era. A property built in 2005 in Letterkenny deserves more scrutiny than one built in 1980 in Cork.

Instruct your solicitor to request a Pyrite Green Certificate on any east-coast property built between 2000 and 2013.

Factor remediation timelines into your decision. A property with suspected but unconfirmed pyrite is not automatically a dealbreaker — but it needs to be priced accordingly and the purchase timed to allow for an application to the Pyrite Remediation Scheme before the November 2026 deadline.

The Ireland First-Time Home Buyer Guide includes a county-by-county risk guide for defective concrete block exposure, a structural survey briefing template, and guidance on how to interpret a surveyor's findings before committing to a purchase.

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