Treacle-black plastic oozes from a nozzle at the base of a small tower in Amsterdam, depositing layer after layer of glistening worms in an orderly grid.
With a knot of pipes and wires rising up to a big hopper, it looks like a hi-tech liquorice production line. But this could be the future of house building, if the architects have their way.
On this small canal-side plot in the north of the city, dotted with twisting plastic columns and strange zigzag building blocks, the firm Dus Architects has started work on what it says will be the world's first house produced by a three-dimensional (3-D) printer.
"The building industry is one of the most polluting and inefficient industries out there," Dus official Hedwig Heinsman said. "With 3-D printing, there is zero waste, reduced transportation costs, and everything can be melted down and recycled. This could revolutionise how we make our cities."
Working for three weeks, the architects have produced a three-metre-high sample corner of their future house, printed as a single piece weighing 180kg.
It is one of the building blocks that will be stacked up like Lego bricks over the next three years to form a 13-room complex, modelled on a traditional Dutch gabled canal house, but with hand-laid bricks replaced by a faceted plastic facade, scripted by computer software.
At the centre of the process is the KamerMake (room builder), a giant version of an open-source home 3-D printer, developed with Dutch firm Ultimaker. It uses the same principle of extruding layers of molten plastic, only enlarged about 10 times, from printing desktop trinkets to chunks of buildings up to 3.5 metres by 2 metres by 2 metres.
For a machine-made material, the samples have an intriguingly hand-made finish. In places, it looks like bunches of black spaghetti; in others, like a fine corduroy. There are lumps and bumps, knots and wiggles, seams where the print head appears to have paused or slipped, spurting out a little more black goo than expected.
"We're still perfecting the technology," Heinsman said. The current material is a bio-plastic mix containing 75 per cent plant oil and reinforced with microfibres. They have also produced tests with a translucent plastic and a wood-fibre mix, like a liquid form of MDF that can later be sawn and sanded.
For now, these plastic blocks, which are printed with a honeycomb lattice within for reinforcement, are back-filled with lightweight concrete, for structural strength and insulation, which would make recycling difficult.
More than 2,000 people have already visited the site, from building contractors to architecture students, and United States President Barack Obama was shown the prototypes when he was in Amsterdam last week.
"It's an experiment," Heinsman said. "We called it the room maker, but it's also a conversation maker. This is only the beginning, but there could be endless possibilities."
Since 2008, researchers at the University of Southern California have been developing a technology, known as contour crafting, that uses a computer-controlled gantry to print structures in quick-setting concrete.
A new dimension
What can be 3-D printed?
The world's first 3-D printed skull transplant was recently carried out at a hospital in Utrecht in the Netherlands, replacing a 22-year-old's malformed skull with a plastic cranium.
US start-up Modern Meadow has printed artificial raw meat using a bioprinter - but a printed hamburger costs about £200,000 (HK$2.58 million).
Developed by open-source firm Defense Distributed, the plans for the Liberator handgun were released online last May, and downloaded more than 100,000 times in two days, before the US State Department had them removed. The Victoria & Albert Museum has a copy of the gun in its collection.
Dutch designer Iris van Herpen has brought 3-D printing to the catwalk, with complex geometrical outfits developed using a multi-material printer, and clothing customised to individual body scans.
3-D printing in space
Nasa is developing technology to print satellite parts in orbit and build objects on the moon, while private firm Deep Space Industries has a project to print spacecraft parts using materials mined from asteroids in a "microgravity foundry". Architect Norman Foster has been working with the European Space Agency to design a moon research base printed from lunar soil.
US adult novelty company the New York Toy Collective gives customers the chance to "scan your own", while Makerlove offers open-source files for people to customise their toys.