The structure is an example of ecologically sensitive design – it is a naturally ventilated, low-energy building – but its real claim to individuality is those bricks: they are the first in Britain to be stuck together with resin-based glue rather than mortar. What the students will not be aware of is the difficulty encountered by the project team. Although it is a splendid thing to be at the cutting edge of innovation, getting the ideas to work in practice can be another matter.
The 2300 m2 three-storey building is rectangular in plan, and split by a central street that lets light deep inside. It has a number of green features, such as exposed concrete surfaces to increase the thermal mass, automated windows to draw air in through the studios and staff rooms at night and prefabricated panels containing straw bales (see "The last straw", overleaf), and the services and steel structure are exposed for examination by the students. But the stars of the show are the stack-bonded brick wall panels, which span from the ground to the roof. The brick panels alternate with full-height windows along the long north and south elevations, creating a vertical effect that is given further emphasis by the strong shadow lines of the unpointed joints. These brick panels form the face of a conventional cavity wall.
Stack bonding is inherently weaker than the more common stretcher bond with its staggered courses, and it usually requires reinforcement set into the horizontal mortar joints. But the beauty of glued joint brickwork is that it removes the need for this reinforcement. Not only that, it is much stronger in tension than conventionally bonded bricks, so openings in the wall do not need lintels. The resin-based adhesive is waterproof, making pointing unnecessary and, when it has been used on the Continent, has speeded up laying time. What is more, the panels can be prefabricated – which the team considered, but eventually decided against on the grounds that the learning curve was too great.
The procedure for laying the brick on site is simple. Adhesive is piped on to an existing course using a hose attached to a special mixing machine. The ends of the brick are buttered with the adhesive, it is placed in position – and that's it. It is known as a "thin-joint" system as the joints between the bricks are only 3 mm wide. The method has been used in Belgium and the Netherlands for more than 10 years, but multinational materials giant Hanson Brick has only just tried to market it in the UK.
Willmott Dixon was the contractor with the job of making the system work at Bristol. It had no experience of the technique to work from, so it sent three bricklayers to Belgium for a week to learn the technique from scratch. However, it wasn't until they started on site that the real learning began.
For a start, the adhesive is trickier to use than it first appears. "The mix has to be just right," comments Eddie Willmott (no relation), one of the team of bricklayers. "If it's too stiff, the adhesive doesn't flow properly, and if it's too wet the bricks sink." These problems were exacerbated by the weather. Between November and March the mixing machine needed cosseting in a heated tent to keep the adhesive flowing freely. "They don't lay bricks in Belgium at that time of the year," says Willmott. "They didn't tell us that."
The mixing machine has changed site practice. For one thing, it needs to be next to the bricklayers as they work, which means that the scaffolding has to be wider. At the end of the day, the machine has to be hoisted off the scaffolding, dismantled and power-washed to get rid of all traces of adhesive. In the morning, it is flushed through with clean water again; this whole rigmarole takes an hour each day. The team also found that they were at the mercy of the machine's reliability, as replacements are not available in the local hire shop.
These complications mean that glued brickwork is not exactly the cure for the skills crisis. Because the joints between the bricks are smaller than normal, and stack-bonded bricks have to be laid absolutely plumb in two directions, the method requires a greater degree of skill than usual. The bricklayers have found it slower too. Willmott reckons he could lay up to 1400 bricks a day using traditional methods; with glued brickwork that is down to about 800. He concedes that he could up this figure to 1000 a day if the mixing machine worked perfectly, if there was a bit more leeway with the precision of laying and if there had not been so many chipped bricks – a problem that the team has had to contend with through the project.
So the technique is not about to replace conventional brickwork – but that might not be the point. What White is happy about is the visual effect: it is like miniaturised terracotta rainscreen cladding, but "a lot cheaper". Despite the steep learning curve, Willmott is also converted: "I am happy to carry on with this method, it's easier." The men in the site hut – Chris Buley, senior building manager, and Marshall Morris, design-and-build co-ordinator for Willmott Dixon – would also use the system again, although they both stress the importance of finding skilled bricklayers with a positive attitude. Even Hanson Brick concedes that the system is not a mass-market product that would appeal to, for example, volume housebuilders.
It is aiming it at commercial projects where the appearance and the consistent quality the adhesive affords gives glued brickwork the edge.
The technologies trialled on this project are already catching on elsewhere. Work has started on a project at Edgbaston cricket ground in Birmingham using glued brickwork, and it will be employed at an art college in Wimbledon.
As for Bristol, it all worked out fine in the end. Hanson can press ahead with their projects having had their UK development work done for them, White has got a striking building, Willmott Dixon has added an extra string to its bow, and the university estates department got their brick building after all.