Whistleblower video shows more cracks in Opal Tower

A video filmed during construction of the Opal Tower has led to condemnation from industry experts, after it appeared to expose more flaws in the building.

The damning footage was captured by a whistleblower three years ago, and aired on A Current Affair tonight.

It shows a massive concrete slab between the 10th and 11th floors that has had multiple cracks patched up with filler.

"We could see daylight from floor to floor, you could drop a two-inch nail straight through, right through to the floor below," the whistleblower, who chose to remain anonymous, said.

"We thought the actual floor should have been cut out, because it wasn't two-three metres square, it was 20 metres long as the vision shows.

"It's not just a square for one unit, it goes across the entire floor."

However, he claimed, the problem area was not cut out and replaced.

Instead, a filler was used to plug up the cracks while another 25 stories were being built on top.

Builders Collective of Australia president Phil Dwyer said the incident could be described as a "cover-up", depending on who had seen it while it was being done.

"It's not just a matter of using a poxy resin to fill up cracks, it's more serious than that," he said.

Images also showed a support pillar on the 10th floor had a huge plastic sheet stuck in it.

Workers had to jackhammer away a large portion of the pillar to remove the sheet.

A tube was then wrapped around the column and workers tipped in concrete by hand to try to repair it.

Construction industry veteran Craig Walker said the integrity of the column, and the of the cracked slab, had been "compromised".

Steel props are also in use throughout the tower, from the basement up.

A Current Affair can reveal props had to be brought in from overseas because the size of the job exhausted local stocks.

Mr Walker said it was only ever a matter of time before industry shoddiness was exposed.

"There is a large proportion who don't have the skills to meet Australian standards," he said.

"If you've got people who don't speak or understand English, they are not understanding orders being given to them, they are not reading plans correctly. If they are misreading steel placement plans, this is the end result."

The private certifier who cleared the tower for residents says it relied on getting the okay from the engineers.

The structural engineer on the job was WSP, the same firm now involved in the investigation into what's gone wrong.

"How can you have an engineering firm undertaking an investigation into their own work?" Mr Dwyer said.

"For heaven’s sake, that's quite inappropriate and out of order."

A Current Affair approached Opal Tower builder ICON, WSP, developer ECOVE and the NSW Planning Minister for comment, but all declined.