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The science: what defective concrete is

Help & AdviceReading time approx 1 min

Defective concrete blocks can contain reactive minerals such as pyrrhotite. Over time, exposure to moisture can cause the blocks to expand, crack, crumble and lose their strength.

The relevant Irish standard is IS 465, which sets out how affected properties are assessed. Understanding the science helps you make sense of your assessment and the works that follow.

This page collects reliable references so you can read the evidence for yourself and feel confident in the process.

Sources

  1. Public consultation: draft I.S. 465 (opens in a new tab)NSAI, 31 March 2025 · nsai.ie · checked 24 Sept 2026The revision of I.S. 465, extended to cover internal sulphate attack.
  2. I.S. 465:2018 (standard, free download) (opens in a new tab)NSAI · nsai.ie · checked 24 Sept 2026
  3. Review offered to downgraded defective block homeowners (opens in a new tab)RTÉ News, 6 November 2024 · rte.ie · checked 24 Sept 2026Research pointing to internal sulfate attack from excessive pyrrhotite.
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