Introduction

The main benefits of precast concrete over other cladding materials are its good strength-to-weight ratio, its mobility and, because it is a non-combustible material, its fire performance.

Precast concrete came into its own for use in cladding during the 1950s and early 1960s with the development of high-rise housing. British architects quickly followed the examples of Le Corbusier's Marseilles Unité block, built between I 947 and 1952, although manufacturers such as Trent Concrete and Empire Stone had been manufacturing high-quality cladding elements in the 1920s and 1930s. Morris (1966) has described the history of the development of precast concrete in Great Britain, France and the USA up to I 964. One of the most famous examples is the LCC flats at Roehampton Lane (facing slab manufacturer Modular Concrete), which marks the beginning of the continuous use of concrete cladding in the UK.

Precast concrete has been used for both non-loadbearing and loadbearing cladding units. Both Morris (I 966) and the Pre-Stressed Concrete Institute (1973) describe the Police Administration building in Philadelphia, built in I 962, as a major step forward in the structural use of precast concrete wall panels.

The three main advantages of using precast as against in situ concrete are:

- speed of erection;

- freedom from shuttering support on site;

- better quality and variety of surface finish, because panels are manufactured in controlled factory situations.

The economics of precast concrete panel production are a function of standardization of mould shape. Similarly, rationalization of panel size and the means of fixing is important for reducing the cost of transportation and assembly. However, obsession with standardization of mould size and lack of research into applied finishes have hindered development of the variety of size and finish now demanded by the architectural profession.

I. I Construction of precast and in situ concrete at the Les Espaces d'Abraxas, a monumental housing scheme near Paris (architect: Ricardo Bofill).

I. I Construction of precast and in situ concrete at the Les Espaces d'Abraxas, a monumental housing scheme near Paris (architect: Ricardo Bofill).

The industry has relied for too long on the range of finishes possible with aggregates. Much of the precast concrete cladding in the UK is in natural stone, granite or brick. However; times are changing. Examples of more sophisticated finishes from Europe, such as epoxy coating in Holland and Germany, and the work of Ricardo Bofill in Paris and Spain (Fig. I.I), have shown the exciting possibilities of the material.

Some projects are now being built in the UK that exploit the use of decorative precast concrete units. A recent example is John Outram's work at Sir William Halcrow's pumping station for the London Docklands Development Corporation and the Thames Water Authority, using painted precast concrete fins. These units, manufactured by Diespeker Marble andTerrazzo, are finished in bright colours, using Icosit paint with a clear lacquer top finish (Fig. 1.2). In this case, intricate curves were formed in the timber mould using two 3 mm layers of laminated plywood.

One of the reasons for the previous lack of research by the industry to provide finishes of this type has been the lack of research into the methods of bonding of the finishes to the concrete surface. Developments in penetrating sealer and primers now allow a smooth non-porous surface to the concrete, thus providing a good base onto which the paint coating can be applied.

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