Defective infill led to structural problems, says geotechnician

SWELLING IN defective infill created “hummocks and mounds” underneath hundreds of north Dublin houses and led to cracking and other structural problems, the Commercial Court has been told.

Dr Michael Maher, a geotechnical engineer with Golder Associates, described the presence of fine-grained pyrite mineral in the infill as a “cause for concern”.

He was giving evidence on the fourth day of a case taken by four construction companies owned by housebuilder Séamus Ross against three companies in the Lagan Group, which supplied the infill used to build up to 750 houses in north Dublin.

Mr Ross’s companies allege that the infill was defective in that it swelled up after use and caused heaving under the houses, with resultant structural damage.

Mr Ross is seeking indemnity of up to €60 million against actions for damages from the householders whose homes developed defects.

Dr Maher, the first technical witness to be called by the plaintiffs, said he had examined up to 50 houses which were undergoing remedial works to deal with the defects. There was no evidence of any movement or other problems with the foundations underneath the houses and the infill. There was no evidence of cracking in the foundations or settlement, or of inadequate compaction of the aggregate, or crushed rock.

He showed slides and produced rock samples for the court which he said showed the presence of gypsum in the infill. Mr Ross’s companies claim that pyrite in the material oxidised, turned to acid and reacted with calcite to form pyrite and produce the swelling.

Dr Maher said his samples were dotted with little mounds of crystals. As the gypsum crystals grew, they got fatter and caused expansion. He said the material used under the houses in three estates – Drynam Hall, Beaupark and Myrtle – contained up to 3 per cent pyrite throughout.

Further, this was in a fine-grained form and a certain amount had already oxidised.

Pyrite was very common, he continued, but usually it came in a chunky, coarse form and could be seen physically. The fine form of the mineralwas a cause of much greater concern by its use as a construction material.

Dr Maher also dismissed a claim by the defendants that polystyrene insulation used under the houses would have absorbed any swelling. The presence of polystyrene would only buy some time before the swelling in the infill manifested itself.