Restoration experts Dave and Robyn Barkman and Steve Martin, from Waitahuna, are carrying out the work for the Nicol's Blacksmith Charitable Trust which has raised about $200,000 to pay for it.
Progress will depend on weather and how much work is uncovered as the weatherboard building is restored.
The forge and all its contents were bought in 1975 by a group of five local farmers, who transferred ownership to the trust in 2006 to plan its restoration and raise the funds.
Before work could start, more than 1600 items had to be catalogued and moved out to a former bus depot.
The builders then moved in to start replacing rotten timber and ensure the building would be structurally sound. The new timber would be stained to match the old.
A fire sprinkler system was also being installed.
The trust planned to turn the forge into a living museum.
