The buttressing, or scaffold supports, will be erected on the western wall of the heritage building following the holiday period.

Wingecarribee Shire Deputy General Manager Operations, Finance and Risk, Barry Paull said the precautionary works were expected to be finalised by mid-February 2020.

"It does mean however that the nine car spaces which directly abut the wall will remain fenced off until the rehabilitation works are complete," he said.

"Our primary focus is to stabilise the building, halt any further deterioration and make the immediate surrounds safe."

Mr Paull said that internal investigations would continue once the external supports were erected.

"Council staff and contractors will begin dismantling the internal ceiling once the internal safety of the building is secured," he said.

"It's then that we'll be able to better assess the structural fault and formulate a plan to fix the problem as soon as practical.

"It must however be reiterated that this is a complex problem exacerbated by the building's age, heritage and previous modifications undertaken over half a century ago."

Mittagong Memorial Hall was built in its present location in 1911. The building comprises of three individual structures that have been combined over the years. These structures include the original School of Arts building, former Mittagong Shire Council Chambers and Mittagong Playhouse.

Building widening and wall removal works were previously undertaken in the 1960's.

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