Failed building boss and departing Senator Bob Day has gone to ground as the fallout continues over the liquidation of his building group which has left hundreds of contractors and home buyers counting the cost.

Debts to contractors and suppliers are reported to top $12.5 million but the construction union has warned that most are likely to get nothing once Senator Day’s Home Australia Group is wound up.

In a statement to staff and contractors, the Family First Senator apologised for the “pain, stress and suffering” the failure of his group will cause.

He’s confirmed he will quit the Senate and has detailed some of his group’s financial issues but has made no further comments.

He has not tweeted since problems with his businesses emerged last month and his Facebook page has been taken down.

A meeting of creditors will likely be held next month, but already there are fears other smaller companies, which relied on work from Home Australia, will collapse.

The Construction, Forestry, Mining and Energy Union says once contractors become creditors, “that generally means they get nothing”.

“For many of those contractors, we’re talking about mum and dad businesses with maybe an apprentice,” CFMEU state secretary Aaron Cartledge said.

“For them to be owed $20,000, it’s a lot of money and it’s devastating for their families.”

The union has questioned Home Australia’s extensive use of contractors, which prevented them getting access to protected entitlements, including redundancy payments and superannuation, despite being “quasi-employees”.

The union has also raised concern for the 200 or so families who had been left with partially-built homes, including an estimated 70 in SA.

Mr Cartledge said while insurance was in place, many would find themselves out of pocket because of delays, questions over the quality of work and pricing going forward.

South Australian Treasurer Tom Koutsantonis urged any home buyers with unfinished projects to move quickly on an insurance claim.

“This is devastating news for families who, in many cases, have put everything on the line to build their dream home,” Mr Koutsantonis said.

The treasurer has also expressed concern for the hundreds of building contractors who are out of pocket because of the collapse, hoping Senator Day could find a way to repay those debts.

“Our small contractors are critical to our economy so Mr Day needs to make good on these debts so we don’t see further damage to the economy as a result of this liquidation,” he said.

It looks like a two-horse race to replace Senator Day in the Senate with South Australian Family First MP Robert Brokenshire and party staffer Rikki Lambert vying for the vacancy.

Mr Brokenshire, who holds a seat in SA’s Legislative Council and is a local dairy farmer, said it was important the Family First executive had ample choice while Mr Lambert said after 10 years working for the party, he felt he was “just getting started”.

Also on Tuesday, a number of the departing Senator’s parliamentary colleagues praised his contribution while the Greens questioned the large donations made by Senator Day’s company to Family First, something the liquidators are likely to look into as they examine the group’s finances.