Upgrades to the King Street building, which opened in 1929, included repairs to the clock tower and the building's iconic sandstone facade - some of which had to be hand-completed by stonemasons.

Governor-General David Hurley will visit the city next Friday to celebrate the completion of the works at a ceremony with a commemorative plaque unveiling and performances by the Australian Army Band Newcastle, the Marching Koalas youth marching band and the University of Newcastle Choir.

The works, which were partly-funded through the council's special rate variation, were initially slated for completion in April 2020, but were delayed due to inclement weather and unexpected repairs.

The intricacies of the project also meant it wasn't a simple, straightforward task.

The upgrade was completed in three stages following a trial restoration to the eastern side of the building in 2009-2010.

"The building was in quite a state of disrepair particularly on the outside," Lord mayor Nuatali Nelmes said.

"Studies and trials found that the metal rods that were holding the faade of the sandstone in place were actually corroding, and that was a very large issue."

Most of the facade had to be removed and replaced. The 'yellowblock' sandstone used in the original construction was understood to have originated from a quarry in Sydney's North Bondi, which is now closed.

In order to investigate and complete the upgrades properly, City of Newcastle worked with the NSW Government Architect's Office and specialist heritage engineers and stonemasons.

"It's exceptionally specialised work and a lot of the work was done by stonemasons by hand, so you can see the time that it's taken," Cr Nelmes said.

"Newcastle City Hall is a rich part of our city's history and is one of our most unique and prestigious buildings."

Mr Hurley said he was delighted to be officially reopening City Hall next Friday.

"Congratulations to the City of Newcastle and all organisations involved in the successful refurbishment of this state heritage-listed building, in which the form, detail and appearance of its iconic faade have importantly been retained," he said.

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