Communications Minister Malcolm Turnbull has entered the fray over Australia's superannuation system, declaring any attempt to allow first home buyers to use their super savings for a deposit to be a "thoroughly bad idea".

"That is not what the superannuation system is designed to achieve," Mr Turnbull said following a speech in Brisbane on Wednesday.

"Housing affordability is a big issue in Australia but, as we have demonstrated over many studies over many years, this is a supply side problem."

Former Liberal treasurer Peter Costello and former Labor prime minister Paul Keating have criticised Treasurer Joe Hockey's idea but Mr Turnbull is the first senior government MP to publicly cast doubt on the merits of using superannuation for home deposits.

His position is also in direct contradiction to that of Prime Minister Tony Abbott, who, on Monday, said that allowing first home buyers to tap into their superannuation was a "perfectly good and respectable idea".

"I can remember back in the early '90s when I was helping John Hewson to draft the Fightback statement, putting in a suggestion to this effect," Mr Abbott said.

Mr Hockey has been undeterred by the criticism and continues to promote the idea that young people could use their superannuation savings to  help buy their first home or pay for job retraining.

Asked about Mr Turnbull's comments, Mr Hockey told Lateline host Tony Jones there were a range of views on the issue.

"Ultimately, Malcolm Turnbull was absolutely right; the best thing you could do for the housing market is to increase supply," Mr Hockey said.

Jones persisted: "No, but let's stick with what Malcolm Turnbull actually said. He is talking about your plan. He said it's a thoroughly bad idea."

Mr Hockey replied it was "not my plan" but one "floated by numerous people in the community".

"I raised the idea in relation to superannuation, arguing the point that we have to, in the context of a longer life span, think about how we can maintain a reasonable quality of life throughout our life, with various points in our life when we're in and out of work," Mr Hockey said.

"Now, at various points when we are in and out of work and we are changing careers, we may go back to study or to retrain. During those periods, we still have to pay the bills. We still have to pay the mortgages. We still have to pay to raise families and so on."

During his speech to the Brisbane Club on Wednesday, Mr Turnbull said the federal government's biggest misstep was failing to make the case for a tough first budget.

And the former opposition leader, who many in and outside the Liberal Party regard as Mr Abbott's chief undeclared leadership rival, cited his own reforms of Australia Post and the National Broadband Network as examples of how to make a case for change.

- with James Massola