Architecture: Cementing the future

UNTIL RECENTLY, anyone who took on the preservation of an old, reinforced concrete building faced growing and often unpredictable maintenance bills. In the UK, concrete repair contracts mainly for Local Authority owners of high-rise housing are now worth pounds 139 million per year, according to the Concrete Repair Association. This lucrative market has fuelled intensive research and produced new concrete treatments that take some of the guesswork out of ownership.

St Anne's Court at Chertsey in Surrey is a reinforced concrete private house that was finished in 1936 by the Australian born architect, Raymond McGrath, for a stockbroker friend, AL Schlesinger. The house stands in 25 acres of parkland on the south slope of St Anne's Hill and has a Grade 2-star listing. Conservation work on the structure was completed last month (August 1998) and an authentic refurbishment of the interior should be finished by Christmas at a total cost of around pounds 1 million.

Reinforced concrete attracted Thirties architects because it combined the compressive strength of concrete with the tensile strength of steel. It allowed radical departure from the gravity-stabilised forms of bricks or masonry.

McGrath took the opportunity to open up the building to light and to the landscape in the way that has become a cliche of the Thirties. The house has a partly cylindrical plan, with a segment removed; so it resembles a large cheese. Enormous, thin-framed, flush-mounted steel windows and a third-floor roof terrace give spectacular views over the garden and the distant countryside. The surface of the concrete retains the marks of the pine boards used in the concrete moulds.

What McGrath didn't know was that, without further treatment, reinforced concrete is programmed to self-destruct. Jimi Fadayomi of the concrete protection company, Sika, says the problem is now well understood. When concrete is made, water in the mix reacts with limey chemicals in cement to produce a very alkaline artificial rock in any shape you want. Steel reinforcing in the concrete adds tensile strength and allows designers to use very slender shapes.

Bare steel does not rust in this strongly alkaline environment and, if that were the end of the chemical story, reinforced concrete would last for ever. But a much slower process, taking decades rather than hours, is a lethal threat to the steel. Carbon dioxide from the air - an acid gas - slowly works its way into the concrete. It neutralises the alkalinity. This process - called carbonation - further hardens the concrete but removes the rust-preventing chemicals from around the steel. The steel rusts, swells, bursts the concrete, the weather gets in, the rusting accelerates, and before long the structure is at risk. Until recently, the best tactic was a regular chipping away and replacement of broken and rusted areas. It was an expensive and, ultimately, hopeless process.

St Anne's Court was bought in 1977 by Phil Manzanera of Roxy Music. By 1997, when he sold it to its present owner, the deterioration had begun. Specialists in concrete restoration, Building Performance Group, decided to use a brand new treatment. They employed specialist contractors to clean the building and repair gross damage - including the hand-replication of board marks on the concrete surface. Then the concrete was soaked with a state-of-the-art steel protection fluid, Ferroguard. The makers of Ferroguard, Sika Ltd, say provided the surface is properly maintained every 20 years, the structure can be expected to last indefinitely.

The Conservation Surveyor for Building Performance Group, Brenda Major reckons they got there just in time. "Because we had access to the new treatment, the structural part, making it weatherproof and structurally sound was a relatively small part of the cost, around pounds 130,000, in a total refurbishment budget exceeding pounds 1 million."

But is St Anne's Court worth the effort? The approach from the road is disappointing. The eaves-less cylindrical frontage and huge flush windows have an industrial look. Brenda Major explains, "In its present state it doesn't quite ring true. There were no windows in the circular part of the third floor when it was built. They were put in in the Seventies."

Whatever the aesthetic compromises on the street side, the south side is a graceful compliment to the vast garden.

The house was designed for a bachelor household and its retainers. The main accomodation and quarters for servants were separate. Subsequent modifications have united the two living areas and brought light into otherwise sunless third-floor rooms. But St Anne's Court will never be an easy-to-occupy family house. Some features do not meet modern standards; like the barely-guarded external spiral staircase. It delighted architects but poses a serious danger to children. The concrete swimming pool is too chilly for modern bathers and will be replaced by a heated, modern pool. Original Crittall window frames will not take double glazing and the listing requires that they be retained. The heating bills will be colossal.

Brenda Major says, "McGrath got some things wrong, like detailing and weatherproofing, and he couldn't work out how to route the rainwater pipes from the roof. I quite like that. It's part of the charm. But St Anne's Court is magic. Its great that there are people prepared to preserve important buildings like this."

Mike Harrison 1998