In October, Waverley Borough Council approved an additional £1.4m after more problems with the building were unearthed.
Concerns have been raised over the increasing costs of the project, with Jane Austin, leader of the Conservative Group, saying it was the third time in two years it had come back for more money.
Funding for the project has been provided by the National Lottery Heritage Fund, Arts Council England, Farnham and District Museum Society, alongside local authorities.
“Willmer House is a building of enormous historical and cultural significance,” said councillor Kika Mirylees.
“Coming out of the wealth generated from the hop trade, Willmer House is noted in particular for its brickwork, rated as one of the finest examples of Georgian brickwork in the country,” said Simon Bradbury, vice chairman of The Farnham Society.
The event is free to attend, but places should be booked in advance, the council says.
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