Slice of inspiration

That's because concrete specialist John Doyle isn't using formwork, and there's hardly any steel fixing. The walls are formed from a sort of sandwich panel, with precast reinforced concrete on the outside and a light filling of lattice girders. Once in place, in-situ concrete stitches the panels to the starter bars and fills the central space.

General foreman Mick Stynes reckons it cuts between 60% to 75% in time. The previous day two joiners had erected 108m of wall. One steel fixer then ties the L-shaped bob bars along the top of the panels to key into the floor slab. On a job like this, Stynes would normally have three fixers on the walls.

The panels have come to the project, an apartment by the River Thames in London, all the way from Germany. John Doyle technical director Peter Goring came across the system when the Concrete Society sent him information from a firm looking to market a similar product in the UK.

"This was one of the few things that came across the desk that we liked the look of straight away," says Goring, who exudes enthusiasm for all things concrete.

A visit to Germany, where he witnessed a 120 sq m house basement go up in seven-and-a-half hours with six men, convinced him it was as good as it looked. It is a common form of construction in Europe with perhaps 50 factories making the panels, many of them in Germany.

The first time John Doyle used the panels was to construct five storeys of flats over a ground floor retail space. Despite a few teething problems which included breaking a panel, the contractor cut the 15 week's programme time to 11. After the slow start on the first floor, the tradesmen were achieving a floor a week, so without the hiccups the construction time could have been eight weeks.

Fancy a quickie?
The great thing about this system is all the simple but clever little details. The outer skin can be cast longer than the inner one, so you have a readymade shutter for the floor slab above. It sits 30mm above the floor slab on plastic shims, so if your site tolerances don't match factory ones it doesn't matter. There are plastic-plugged holes (called 'quickies') that you unblock to attach your acro-props to in order to get the wall vertical. And unlike some precast systems, there's no interesting connection details – just starter bars the same as with any traditionally built wall.

Depending on the application, walls can arrive on site with electrics installed, or points for fastening handrails to be attached pre-lift. That eliminates scaffolding and it's good for safety.

Perhaps most surprising, conditioned as we are in the UK to believe that only repetition can make offsite economical, there is no problem in each panel being different. This is because of the highly mechanised German factories that see huge production lines where robots mark out panels, and sometimes place stop ends and rebar as well before the concrete cures in huge ovens. The shape and size can vary, and the wall thickness, from 200mm up to 420mm.

There was a little resistance from the joiners the first time they used the panels, but that has passed. Goring puts it down to fear that their jobs were in danger. But you need to use a chippie rather than a labourer for this job, says Stynes, because the line and verticality have to be right.

This is the fifth job for John Doyle with the panels and there have been lessons to learn on the way. For example on the first couple of projects they allowed 10mm tolerances for the joints, but that was too tight. Now they have 20mm, which allows you to pull back any creep along the way.

The panels can't replace traditional concrete everywhere. For example, on the current job John Doyle will only use them to construct the basement. Another point to consider is that you need good technical preparation. "You have to do a lot of work in the office to get the holes and the dimensions right," says Mo Hurch, contracts manager.

And then there is the transport to consider. Costs are significant, because panels come all the way from Germany, and their dimensions mean there is the additional cost of a movement order, required for loads more than 2.4m wide in Germany and Belgium, to pay for. Goring has a plan to eliminate the movement order fee once the firm is using sufficient panels. He will invest in a toaster-like rack to transport the panels vertically, as they do in Germany.

But if it's such a great system, why is no one making it in the UK? The mechanisation required makes it expensive. It would take an investment of some £8m to set up a factory.

So with the substantial transport costs, savings aren't huge yet. The first couple of jobs, reckons Goring, were cost neutral. Now they might be saving around 10%. But for that you're getting a beautiful and consistent concrete finish, so good it can be just painted in, say student accommodation, together with shorter times, and a safer working environment.

There are more savings to come, says Goring. John Doyle is pricing up future projects such as PFI hospitals and prisons, hotels and student accommodation. "We are finding more and more applications," says Goring with glee.