The refurbishment of Bristol’s Colston Hall will cost “millions” of pounds more than the £52.2m budgeted, according to the city’s Mayor.
The extra cost has come from discoveries of asbestos, old well shafts and unstable building supports.
Marvin Rees said:”Bristol is not awash with money, we couldn’t sit with an unusable concert venue, we had to take the challenge on.”
The rebuild was due to finish in 2021, but coronavirus is likely to delay it.
The hall will have a new name when it reopens after the Bristol Music Trust pledged to sever ties with the slave trader Edward Colston.
Mr Rees has not disclosed the exact cost and said the information will be available to councillors in September.
Discussions are now taking place with the agencies funding the project to ask for extra money.
The hall is a mixture of buildings after fires in 1898 and 1945 led to multiple rebuilds.
The latest renovation to completely redesign the hall’s interior, which was largely unchanged since the 1950s, began last year.
Construction staff working through lockdown discovered Elizabethan wells and Victorian stoves from the building’s original heating system.
Richard David, from Willmott Dixon Construction, said:”Finding the wells was quite exciting.
“There were also rooms in the building that nobody knew existed.”
A report to Bristol City Council, which owns the hall, says the columns holding the building up were found to be hollow and weaker than first thought.
The report also lists rotting joints, wall voids and asbestos as problems that need to be dealt with.
“Some remedial work needs to be done, in many ways this was inevitable,” Mr Rees added.