A decision by the contactor to accelerate the project means the $13 million makeover of the Makatote rail viaduct will be finished three months ahead of schedule.

The historic viaduct on the North Island Main Trunk line a few kilometres south of National Park has been sandblasted, repainted and strengthened in some places by the contractor, TBS Farnsworth.

They started work in October 2014 and according to KiwiRail project representative Mike Keenan the last of the scaffolding will be removed by the end of this month.

"Apart from some minor touch-up painting the job's done," Mr Keenan said.


He said TBS Farnsworth decided to speed up the painting and sandblasting programme to avoid any problems with wet weather. Both the remote location of the viaduct and changeable weather posed special challenges for workmen on the job and that was the main reason to get the job done sooner.

This week the scaffolding on the tallest central pier was being removed.

"The thing is the blasting and painting of the bridge has been done and that was the major part of the project," he said.

Mr Keenan said KiwiRail was "thrilled" with the job the contractor had done.

"Regular train services continued across the viaduct throughout the project. We had a temporary speed restrictions in place but there were no disruptions at all," he said.

A TBS Farnsworth spokesperson said stripping lead-based paint off the 296-metre long and 80m-tall viaduct was the one of the most complex jobs the company had undertaken.

The viaduct is more than 100 years old and was last painted in 1959 and the project also involved the Department of Conservation, Heritage NZ, local councils and iwi.

A key requirement was protecting the environment in and around the Makatote River beneath the structure. It's an area that is home to the rare whio (blue duck), kiwi and rainbow and brown trout.

While the old paint was sandblasted off the steelwork, the waste had to be collected inside plastic wrapped around the structure and then vacuumed up to a storage site about 100m south of the bridge for later disposal.