Cladding on Brisbane's Princess Alexandra Hospital will be removed after testing revealed it was more combustible than previously thought.

The cladding, which measures two-and-a-half times the size of the Lang Park playing surface, will begin to be removed in about four weeks.

Public Works Minister Mick de Brenni said it could take 18 months to remove and replace the cladding.

For an amount of time, the hospital will not have external cladding.

He assured the public the hospital was safe and would continue operating during the works, adding the hospital had 13,000 fire sprinklers.

Mr de Brenni said there had been a systematic failure of Australia's building regulation system.

"I have made this a priority of regulators at a state and territory level, and Queensland will make sure there is comprehensive reform to the building codes system including the Australian Building Codes Board, the National Construction Code and building standards," he said.

The hospital was tested following London's Grenfell Tower inferno, with Mr de Brenni assuring the public at the time that the hospital "remained safe".

Entire panels from different sections of the hospital, equating to 80 square metres — or 20 king-sized beds — was sent to Melbourne for extreme testing under real fire conditions.

Nurses union doesn't want health budget cut

Queensland Nurses and Midwives Union Secretary Beth Mohle said there was going to be some loss of shading as a result of the cladding.

"But issues like that will just have to be managed," she said.

The union did not want the Health Department to be totally financially responsible for the clean up, saying the Public Works Department should also be chipping in.

"It should not result in any cuts to health budgets."