The aesthetic possibilities of in situ concrete have long been recognised by the architects of churches and other public buildings, but the use of in situ concrete in domestic interiors was, for many years, confined to a handful of individually designed private dwellings.
Now, however, thanks largely to the efforts of award-winning architects such as Azman Owens and Jamie Fobert, in situ concrete as an interior finish is perceived by a wider public as being not only über-fashionable, but also achievable and affordable.
Yet many architects, according to architectural concrete consultant David Bennett, fail to understand what they can achieve with in situ concrete.
Even with the practically limitless range of bespoke colour combinations and finishes, says Bennett, they remain reluctant to incorporate the material in their designs. This is despite the fact that it could potentially offer considerable cost savings over, for example, terrazzo tiles when it comes to providing large areas of attractive and extremely durable flooring.
While quick to describe the technical challenges of casting such a floor, Bennett is even quicker to dismiss the need for specialist concrete contractors.
He says contractors only have to be aware of the need to avoid excessive surface tamping (which brings sand, cement and water to the surface), and the importance of surfaces being absolutely true to enable effective cutting and polishing. Laying a terrazzo floor in situ, he maintains, requires little more than 'a competent contractor with the right equipment'.
What is important when working with in situ concrete, whether on floors, walls or other surfaces, is how contractors are instructed. 'Architects need to give information directly to the people who are actually doing the work, ' Bennett insists. Contractors have not been challenged enough in this area, he adds, nor have they been given enough help and guidance to extend their abilities beyond carcass-grade in situ concrete.
The reason? People turned their back on concrete, Bennett says, 'after the Modernists and Brutalists did it to excess, and developers exploited it badly for cheapness'. Consequently, in situ concrete is both misunderstood and underused.
He laments the UK's 'poor craft skills', asserting that a good joiner is the secret of good in situ concrete work. This, and the quality of wood - or indeed other materials - used for formwork.
He urges architects to think of formwork as furniture; it is, after all, reusable and that justifies its often high cost.
Despite the UK skills shortages, Herzog & de Meuron is pleased with the quality of in situ concrete it has managed to achieve at the Laban dance centre in Deptford. The Swissbased firm is a prolific user of in situ concrete, having pioneered a number of finishes and applications.
It was, says associate Michael Casey, the first practice to incorporate glass in concrete as well being a pioneer of screen printing concrete. 'We use concrete in a way that's responsive to the contractor, ' he explains, 'and while we can produce very beautiful concrete in Japan, it's easier here to work with lesser tolerances'.
A growing number of architects in the UK are beguiled by the unpredictability of in situ concrete, says Bennett. They regard it as the closest thing to a natural, manufactured product.
The scatter of stones in an in situ cast terrazzo floor has, he says, 'the randomness of pebbles on a beach'. And it is this randomness, he adds, which gives in situ concrete its unique form, beauty and character. But here, too, there is another stumbling block: 'The fact that it is monolithic - one solid slab with no joints - means the only sample you can do is the entire thing.'
And without samples, architects are reluctant to specify in situcast concrete.
Bennett describes how he was brought in as a 'concrete doctor' halfway through a recently completed contract to build RIBA's London Building of the Year 2003, a four-unit apartment at No 1 Centaur Street, close to the Eurostar viaduct at Waterloo Station.
In addition to prescribing the successful grit blasting of honeycombed in situ concrete walls, he provided a 'simple-to-follow recipe' for the terrazzo flooring specified by architect de Rijke Marsh Morgan (dRMM) for the building's communal circulation areas. A local building firm laid this floor successfully, Bennett claims, by adhering closely to his instructions.
Michael Spooner, an associate with dRMM, admits that this project was 'a steep learning curve', and that he learned a great deal in terms of controlling the concrete process on site, including strategies for constructing formwork. 'We realised that we had to be hands-on and work very closely with the chippie.'
Bennett praises the 'excellent' joinery skills of London-based contractor Varbud, and its positive contribution to Azman Owens' RIBA Award-winning concrete house in Aberdeen Lane, Islington. A general building contractor, Varbud had worked with Owens on a number of projects before this one, but none that required such large amounts of in situ concrete.
Joyce Owens says that she decided to employ David Bennett as concrete consultant early on in the project, 'because it included the casting in situ of load-bearing walls'.
Bennett sent the contractors on a training course and showed them how to use a special poker to remove air bubbles. The combined expertise and close working relationship of the various parties involved in this project resulted in a stunning testament to the beauty and versatility of in situ concrete. The silky internal walls were poured behind birch-faced formwork panels that had been lightly oiled with a high-performance chemical release agent. Everything was screw-fixed from the back of the panels, says Bennett, ensuring that the contact face was free of potential blemishes or splits.
While Owens admits the clients on this project were initially suspicious of in situ concrete, fearing that it might appear cold, they were happy to proceed once they had seen some other buildings with concrete interiors.
And the finished house is very warm in appearance, she says, 'thanks to the unbelievable contrast between the rich reddish timber and the concrete'.
Owens insists that what she likes most about in situ concrete is its unpredictability - 'the fact that you never know quite what you're going to get'. And unlike the uniform finish of pre-cast, she adds, 'it's so organic'.
'I like the fact that concrete is fluid, as oppose to all other materials, which are unit-based, ' says Jamie Fobert, of Jamie Fobert Architects, whose quirky and spatially sensitive Anderson House, an entirely concrete building with no exterior walls, clinched this year's 2003 Award for Building in an Historic Context.
The client approached Fobert after seeing his concrete-dominated interior for Cargo, a restaurant/club in Shoreditch, and the concrete furniture his firm has created for several Aveda cosmetics shops.
According to Fobert, the client liked the polished effect his team had achieved on in situ concrete walls at Cargo by using polythene sheeting inside the formwork.
'We developed this further, ' Fobert explains, 'acknowledging that a domestic scheme needs to be at a more human scale.' Fobert used neither concrete consultants, nor specialist contractors on this project. 'What we were not looking for was something monolithically flat.'
He explains how the idea of lining formwork with plastic came about by accident when, on a job in south London, plastic sheet-lined foundations were inadvertently left protruding from the ground, and he realised that polythene can imbue poured concrete with a glassy, reflective quality.
Fobert's free-form, experimental approach certainly paid dividends with the Anderson House, and his practice seems well and truly hooked on the further use of in situ concrete, for domestic and commercial interiors. His advice to nervous architects considering the same is to find a brave client. 'You can't force concrete on someone who doesn't want it, ' he insists.
Joyce Owens, on the other hand, has successfully proved that sceptics can be made to appreciate the virtues of in situ concrete. Her unequivocal advice to architects is to get in an expert: 'Someone like David Bennett - he gave us a seminar and made us understand the possibilities and pitfalls of working with in situ concrete.'