Revised defective blocks standard finally acknowledges pyrrhotite as primary cause of crisis

After almost six years in gestation, the National Standards Authority of Ireland (NSAI) has finally published its revised IS 465, the testing protocol that underpins the State's defective blocks grant scheme.

The new standard, which for the first time acknowledges pyrrhotite as a primary cause of degradation in defective blocks, came into effect at the end of May.

100% Redress Party TD Charles Ward has welcomed the new standard, praising the efforts of years of campaigning by affected homeowners alongside engineers, geologists, scientific experts and public representatives. He paid particular tribute to homeowner and scientist Professor Paul Dunlop, together with Swiss academic Dr Andreas Leemann, for their important contribution to advancing research and understanding of the root causes of the defective blocks crisis.

Read more: Parts of the defective blocks scheme are back-to-front says TD Charles Ward

The NSAI says the revised standard, which was ordered by the Government in November 2021, is the product of detailed examination of evolving scientific and engineering evidence, alongside extensive engagement with a broad range of stakeholders.

While the original IS 465, drawn up in 2018, focused on mica and pyrite as the causes of defective concrete, the 2026 revision acknowledges that iron sulfide minerals such as pyrrhotite cause cracking in blocks and concrete.

Once the presence of iron sulfides is detected in samples taken from affected homes, the engineer shall recommend the demolition and rebuilding of all affected concrete block elements, as this is the only effective solution.

Mica remains on the list of problematic minerals. The protocol acknowledges that its presence on its own can adversely affect the strength and durability of concrete, but its role as an accelerator of internal sulfate attack causes the most severe and rapid degradation of blocks.

Significant emphasis is also placed on the potential for future degradation of concrete blocks, something that was not provided for in the original protocol.

However, the revised protocol is less certain on the extent of damage caused to concrete foundations where mica, pyrite or pyrrhotite are present, either alone or together. It says more research is needed on foundations as, being buried beneath the ground, the deleterious minerals are not oxidised (exposed to the air) and are therefore not liable to the same damage as blocks above ground. However, it does allow for the removal of foundations on a case-by-case basis where recommended by an engineer who has obtained further expert support.

“I also note the sections relating to foundations, where the standard acknowledges that uncertainty remains regarding long term performance in some circumstances,” Deputy Charles Ward said in a statement. “It is important that a precautionary and consistent approach is applied where risks are identified.”

Deputy Ward acknowledged that the testing protocol relies on the judgement of professionals - engineers, geologists and scientists - and said it is important that the process is transparent and subject to independent oversight.

“Because these decisions can have major consequences for homeowners, consistency, transparency, and independent oversight will be extremely important in how the standard is applied in practice,” he said. “Ultimately, affected homeowners need confidence that the system will deliver fair assessments and durable long term solutions.”

One final change of note is that IS 465 replaces the term 'dwelling' with 'building' throughout. While the entire focus of the defective blocks crisis to date has, rightly, centred on homes, all types of buildings - whether schools, car parks, farm buildings, commercial premises or sports clubs - are also among the tens of thousands of structures affected.

The implication is that the new protocol will, when the time comes, be valid for the assessment of non-dwellings.