The centrepiece of the Port Arthur Historic Site is in serious decay and it may be, in part, because of the convicts who built it.
The chairman of the site's management authority Barry Jones says at least $6 million is needed to restore the penitentiary.
Mr Jones has told a government business hearing in Hobart the towering 182-year old building is crumbling and a new frame must be built to hold it up.
Part of the problem could be because of the convicts who helped build it.
Mr Jones says there are stories of sabotage in which convicts mixed salt water with the mortar to undermine its strength.
"Parts of the building only meet 30 per cent of the engineering loads that we regard acceptable in domestic building; some parts only 10 per cent," he said.
"So clearly something major has to be done and sooner rather than later." The State and Federal Governments are yet to commit funding to cover the entire cost of the repair work.
Heritage Minister Brian Wightman says the State Government has contributed about $500,000 and further funding requests will be considered in the budget process.
The authority's chief executive Stephen Large says the board will be fundraising elsewhere.
A fundraising foundation is being proposed for emergency repair work.
"We have to raise the money as soon as we possibly can, not tomorrow, but I think over the next 12 to 18 months we need to be in a position where we commence that work and do that," he said.
Port Arthur is a world heritage-listed site.