Fairfax Media revealed last month Anthony Steve was being hit with tens of thousands of dollars in unexpected costs, after the bricks were unearthed on his Griffith block.

The Steves went halves with their friends the Jeffcotts in the $1.6 million block, and had planned to build a duplex for their families to live in.

But builders dug up the footings of the old house, which were covered in a grey substance, which put their project on hold indefinitely.

Laboratory testing showed it was Fluffy asbestos, despite the block being tested and signed off on.

The government blamed old building practices, where demolition rubble was used as fill in backyards.

The sales contract for former Mr Fluffy blocks gives no guarantees the remediated block is asbestos free, a clause which has been heavily criticised by Canberra's legal fraternity.

In his response to the Steves and Jeffcotts on Tuesday, Mr Gentleman pointed to this clause, and said anyone concerned about their exposure should seek medical advice.

Mr Steve said hiding behind the clause was "unconscionable".

He questioned why special care was not taken to remove all contamination from the site, given the demolition company knew the home had been extended, which increased the risk that contaminated rubble had been buried on site.

However Mr Steve pointed out the bricks were found in the footprint of the original home, where footings had been left in-tact and only uncovered by deep excavation.

"We are extremely alarmed and disappointed with the response from the ACT government regarding our situation," Mr Steve said.

"At its core, the ACT government did not remediate our block as they were required to do under the Loose Fill Asbestos Insulation Eradication Scheme.

"To leave Mr Fluffy asbestos on a block that had supposedly been remediated shows poor management, lack of oversight, substandard quality controls and an inadequate execution of services."

He said Mr Gentlemans "careless" response to seek medical advice showed no concern "with the public safety of the people they serve, their voters".

The revelation failed to deter buyers eager to get their hands on one of the rare blocks at the year's first mass Fluffy auction earlier this month.

However, legal experts have warned potential Fluffy block buyers to get legal advice before bidding on a block, while the CFMEU even suggested the new owners should undertake an asbestos training course.

However Environment, Planning and Sustainable Develoment Directorate's deputy director-general for sustainability and the built environment Geoffrey Rutledge tried to assure buyers the sites were suitable for residential reuse.