Behind the elegant brick facade of The Hotel Britomart lies a feat of structural engineering that blends heritage, modernity and more than a little artistry.
Like many of the refurbished heritage buildings of the nine downtown waterfront blocks that make up Auckland's Britomart precinct, The Hotel Britomart is made of brick. But unlike its 140-year-old neighbours, The Hotel Britomart’s brick walls weren’t laid by hand, one-by-one, but were constructed in a factory in Auckland in a feat of engineering, manufacturing and artistry.
Karen Wrigley is a project manager at Wilson Precast, one of New Zealand’s most prominent concrete panel manufacturers. In a vast hangar in East Auckland, she led the construction of the dozens of brick-clad concrete panels that form the 10-storey structure of the hotel.
Although brick-clad concrete buildings are found throughout America and Europe, The Hotel Britomart is the first time the construction technique has been used in New Zealand. Creating the panels meant working with a demanding new system, from the hefty steel reinforcing cages inside, to the elegant brick exterior.
“It came with its challenges,” says Karen, who is prone to dry-humoured understatement. “The cages, for example, are heavier than some panels this factory makes. They’re so dense you can’t even get a finger between the bars in some places. That meant we couldn’t use a standard concrete mix – we had to use a finer mix so the largest pieces of aggregate would pour between the bars.”
Each panel was constructed by laying bricks on a wax-lined rubber tray with indentations to hold each brick in place. Once laid, Karen would inspect the layout, ensuring that the colour mix looked right. “Sometimes, because I came in fresh, straight away I could see a patch of the same colour all together, so I got the guys to move them around. There is a bit of art to it.”
Next, the steel reinforcing cages were suspended above the panels – a job that could take a full day in itself. Then timber formwork for the panel sides and window cut-outs was installed, and the concrete poured. Afterwards, the panels were cleaned, checked for cracked or tilted bricks to replace, left to cure, and given final surface touch-ups before delivery to site.
It was slow work. Small panels were made at a rate of two a day, but the large panels, which could weigh up to 20 tonnes, took the team a day or more to get to the week-long curing stage.
What’s more, the margin for difference between the panels – known as ‘tolerance’ – was incredibly low. Because the panels stack and lock together between storeys, they had to be virtually identical in size, with window cut-outs that could not vary by more than a couple of millimetres in order to seal correctly. Given that panels were constructed anew every time, the engineering accuracy achieved was phenomenal.
Throughout construction, Karen travelled between the factory and site, double-checking measurements as each storey was installed every three weeks. “It’s one thing for me to do it all correctly on computer. It’s another to install it all as per the computer,” she says. “Human nature is human nature and things move and sites change. That’s tolerance.”
The seamless finished result belies the intricacy of the engineering. “The irony is that because Karen and the team at Wilson have done an amazing job, you’ll never notice it,” says Tom Webster of Cheshire Architects, who worked closely with Karen on the execution of the design. “All that complexity and hard work is hidden; you’d only notice it if something was slightly off.”