Unique design challenges faced the structural engineer responsible for the safety and stability of a ‘melting house’ art installation in London’s Southwark Street
Artist Alex Chinneck - fresh from his well received ‘floating market building in Covent Garden - will reduce his latest exhibition to a mound of wax by 18 November.
At first sight a conventional two storey brick-built house on a 9.4m x 4.7m footprint, the structure is actually made up of a wax skin topped with a lightweight roof.
Speaking to AJ sister-title NCE. structural engineer Smith and Wallwork principal Simon Smith said the first challenge was ‘how to build it so it didn’t fall down’.
He added: ‘The walls are more than 5m high and only 75mm thick, and there was very little available information how the wax would behave.
‘We were particularly concerned about elastic deformation and creep, as well as the effect of ambient temperature variations. And some sections of the walls would be more exposed to sunlight than others – even in late October this could have been a problem.’
Preliminary estimates based on internet data suggested the walls might shorten by less than 10mm under self weight. More information from the wax manufacturer on the likely softening at higher temperatures highlighted the need for some basic research. Operating on a tight budget, Smith opted to carry out tests in his own garage.
These produced more realistic predictions.
‘We were looking at something more like 25mm settlement. But this could rise to 75mm if the wall got really warm.’
There was never any intention of supporting the roof directly off the single skins of wax bricks, Smith adds. This would have made the melting of the house very unpredictable and potentially catastrophic. Instead, the roof sits on six manually operated Genie SuperLift Advantage telescopic lifting platforms, which lower the roof as Chinneck melts away the brickwork with a high powered hot air gun over a four-week period.
Chinneck has been responsible for a number of art installations requiring serious structural engineering input. He worked with wax supplier Darent Wax – whose main product is pellets for leg waxing – to develop a blend of paraffin wax and ethylene vinyl acetate (EVA) polymer that could be cast in beds of terracotta sand to produce a brick that mimicked the real thing convincingly.
‘We needed nearly 8,000 bricks, which we produced at a rate of 200 a day,’ Smith reports. ‘To speed the re-use of the moulds, we transferred them to a mobile cold room as soon as the wax was poured.’
Brick size is 65mm x 75mm x 215mm, and each has 25mm-diameter holes drilled into it to create mortar plugs. Door, window frames and glazing are all wax as well. In all, some 85m3 of the substance was needed for the installation.
Many normal building design loads, such as snow on the roof, could be ignored due to the short design life, and fire resistance is not a factor. Wind loads are another matter. The building’s city centre location meant turbulent conditions could be expected, although design loads could be reduced as there would be no exposure to winter gales.
Wall stability comes from diagonally braced 50mm x 150mm timber wind posts at 900mm centres connected to the wax brick skin by cavity ties.
As these posts have to reduce in height progressively as the walls melt and the roof is lowered, Smith first experimented with telescopic carbon fibre fishing poles, but these turned out to be far too flexible. These wind posts also have to stabilise the roof during its descent.
Connecting the roof to the wind posts are steel angle plates with slotted holes. As melting proceeds, the roof descends in 200mm stages, the wind posts slide through the fixings and the surplus timber is cut away.
At their feet, the wind posts are fixed to angle brackets welded to the 150mm x 150mm x 10mm SHS base frame that carries the walls, which in turn is shimmed off the existing hardstanding.
‘We had to keep the weight of the roof as low as possible, so it’s very lightly built,’ Smith says. ‘In total it’s around 1t. The very realistic ‘slates’ are in fact made of plastic and hand painted by scenic artists.’
Low roof weight is essential as the construction process was the reverse of the norm. The entire roof had to be lifted 5m into the air first and stabilised there by temporary timber props at the corners while the walls were built underneath.
A team of professional bricklayers from Laing O’Rourke enjoyed themselves learning how to adapt their skills to deal with the wax bricks, Smith reports. They first had to come up with an effective mortar. As the wax bricks draw no water out of the mortar, unlike conventional bricks, a normal mortar was reluctant to adhere to the wax. A much stiffer, high cement content mix had to be used.
Once Chinneck’s destructive work is complete, most of the 8t of wax will go for recycling as firelighters, and the Smith/Chinneck team will turn its creative skills to even more extreme challenges.
An eye for the unusual
Enigmatic titles are a trademark of much of artist Alex Chinneck’s recent work. Officially the ‘melting house’ is known as ‘A Pound of Flesh for 50p’, and is part of the award-winning Merge Festival at London’s Bankside.
It celebrates the history of an old candle factory that operated in the Bankside area two centuries ago, and is the fruit of a 12-month collaboration between the artist and structural engineer Simon Smith, along with wax producers and chemists.
Another recent high profile collaboration with Smith resulted in ‘Take My Lightening But Don’t Steal My Thunder’ in London’s Covent Garden, where sections of the famous Market Building appeared to hover in mid-air. (NCE 3 10 14).
And at last year’s Merge Festival, ‘Miner on the Moon’ featured an upside down house and attracted a lot of attention.
“Many of my ideas need serious structural engineering input,” Chinneck says. “Working with Simon is great – he’s never once told me that what I’m asking is impossible.”
Current projects include a ‘house full of fish’ in Belgium, another optical illusion, and Chinneck is also seeking funding for a ‘fallen windmill’, where the sails are stuck in the ground but the tower rotates.
He has another vision, potentially the most eye catching so far.
“I’d love to rebuild one of Battersea Power Station’s iconic chimneys full scale – but with a knot in it!”
Sponsorship is the vital element in such projects. For the melting house, the funding came partly from Merge curator Illuminate Productions, business improvement district Better Bankside and the Tate gallery.
Laing O’Rourke supplied labour, Select Plant Hire loaned equipment, and there was further support from across British industry.
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