'Superglue' saves heritage structure

Spray-on cement has brought the 38m brick chimney at Victoria Park Market in central Auckland to near New Building Standard for strength.

The 38m brick chimney at Victoria Park Market was considered a liability if Auckland was ever struck by a large earthquake. But it is now nearly unbreakable thanks to a New Zealand-made innovation which has glued it together from the inside.

Building and Construction Minister Maurice Williamson says it is an example of how new technology could help salvage quake-prone heritage buildings within the Government's new earthquake-proofing deadlines.

Most of New Zealand's earthquake-prone heritage buildings must be either strengthened or demolished by 2033. The most precious structures, classed as Category 1, have another 10 years to be upgraded to more than 33 per cent of the new building standard (NBS).

The 105-year-old Victorian chimney in Freemans Bay was made of unreinforced brick, and fell below this NBS threshold, which meant it could collapse in a moderate earthquake.

Glenfield-based company Reid Construction Systems used a hydraulic hose to pour flexible concrete into the inside of the chimney, which has now brought the structure close to 100 per cent of the NBS. The technology was developed with help from the University of Auckland engineering school.

Mr Williamson said: "They've got this spray-on cement which they spray on the back of any facade of these buildings. When you try to pull the bricks off it, the bricks would snap rather than let go, the adhesion was so strong. You could bend the whole wall out of shape by a 45 degrees and still all the bricks would stay in place because this stuff [is] almost like a superglue."

During the consultation on earthquake-proofing deadlines, Auckland Council and other local authorities expressed concern about what the new policy could mean for its heritage buildings, some of which would require costly and complicated upgrades.

Mr Williamson said the Victoria Park rebuild showed that even unreinforced masonry buildings could be earthquake-proofed without crippling costs.

"There're a lot of smart engineering brains finding solutions to these things. So I'm not as pessimistic as some people that this means a huge amount of our heritage buildings won't survive this and will have to come down."

He pointed to other engineering initiatives such as the "tightening" of unreinforced masonry walls in Wellington, where rods were drilled through walls at a 45 degree angle, then screwing mechanisms used to strengthen the building.

This procedure was estimated to have cost the owner of an $800,000 building around $20,000.

The total cost of restoring the chimney was believed to be around $600,000. Similar technology has been used to upgrade other brick buildings in Freemans Bay, Ponsonby, Karangahape Rd, and some University of Auckland buildings.

Unreinforced masonry killed 40 people in the Christchurch earthquakes.