The strength of concrete used in the ill-fated Tongaat mall was in places less than a third of what it should have been, an inquiry heard in Durban on Wednesday.

"This concrete failed to reach even half of what is required. That is a catastrophe. It means collapse," the labour department's occupational health and safety manager Phumudzo Maphaha said.

He heads a three-man commission investigating the collapse.The weak concrete was used in the portion that collapsed on November 19 last year, killing two people and injuring 29.

t failed to achieve the required strength of 30 megapascals (MPa) after 28 days of curing.

"The concrete could not even reach one third of what was required," Maphaha said.

He was speaking during testimony of Roderick Raw, the Durban laboratory manager for Contest, a company which tested the concrete at the mall while it was under construction.

Maphaha asked why Raw's laboratory had not raised the alarm over the test results.

Raw said the results would be sent to the builders, Gralio Precast (Pty) Ltd, and he assumed the person receiving them would take action.

He said Gralio never queried the test results.