Over 100 houses under construction as part of the regeneration of Ballymun in north Dublin are being tested for the presence of pyrite, a substance that when it reacts with water can expand and cause cracks in walls and floors.

Just last month, Ballymun Regeneration Ltd (BRL) announced its ambitious plans to build 5,000 houses to replace Ballymun Towers and apartment blocks will be delayed by at least two years after its funding was cut from €80m last year to €45m this year.

Mary Murphy, spokeswoman for BRL confirmed builder James Elliot Construction has started tests on 124 houses in Ballymun after suspicions were raised that the houses may be contaminated.

Murphy said the same builder started repair work this month on the newly built recreation centre in Ballymun which was confirmed as being contaminated with pyrite.

In the meantime, Elliot has constructed a temporary recreation centre at the back of the damaged building which is used by close to 1,000 residents every week.

The use of pyrite is currently the subject of a separate multimillion euro damages claim at the High Court. Menolly Homes and other developers are suing the Lagan group claiming around 750 houses it built have been structurally damaged after using pyrite-contaminated infill from a Lagan Group quarry in north Dublin.