August_1966 — Page 91

A

materials and equipment

PRECAST process which may bring a new approach to industri- alised building has been developed by a British firm, D. A. Models, Ltd., 108 Woodstock Road, London, W.4. The new process is the outcome of several years' work on the use of glass fibre techniques for formwork.

Glass fibre moulds for concrete offer certain advantages over moulds made from more traditional materials such as wood or steel. Although timber formwork is the lowest in initial cost, it is easily damaged, de- teriorates fairly quickly, and so limits production runs. Steel formwork is ideal for long production runs, but it is expensive to manufacture and its weight does not make handling or transportation easy.

Reinforced glass fibre moulds, however, are light and strong and can be used hundreds of times, yet their cost can be recovered after as few as eight casts have been made. Al- though the building up of a glass fibre mould requires skill and experi- ence, the ease with which this ma- terial can be moulded into virtually

any shape allows the architect to make full use of the plastic proper- ties of concrete.

From their first use on portal frame buildings, glass fibre moulds have been introduced to other bran- ches of the concrete construction in dustry and uses have been found for it in producing columns, bridge sup- ports, pre-cast sections for reservoirs, and motorways and coffered and rib-

A typical example of a building using pre-cast concrete units is illus- trated below.

Eight glass fibre moulds were de- signed, which altogether produced. 448 structural concrete units. Each face unit is 14 ft. 111⁄2 in. wide by 10 ft. 3 in. high (4.5 m. wide by 3 m. high), contains three windows and weighs 41⁄2 tons. Corner units are designed differently and contain only. one window.

The building is 15 storeys high, 14 of which consist of pre-cast concrete units, and occupies a ground area 1671⁄2 ft. by 46% ft. (54 m. by 14 m.). Steel reinforcement was fabric- ated and fixed at ground level.

For this building moulds of the contact_moulding type were produc- ed. First a positive replica of the building unit was made from timber or plaster to meet the architect's exact requirements for texture and embellishment.

This "mock-up" was prepared with

GLASS FIBRE MOULDS

bed floors. Flooring in multi-storied car parks and other buildings has utilised reinforced glass fibre rib-span shuttering, and glass fibre pan moulds have been used for the flooring in hospitals and schools.

On columns the column boxes are made of two units, each with vertical flanges: they vary in height up to 30 ft. (9 metres) and in diameter be- tween 9 in. and 6 st. (23 cm. and 1.8 m.).

Close-up of precast corner units show- ing high quality of finish

Assembled

glass

fibre mould for a corner unit

shellac varnish, silicone polishes and a parting agent, and the mould sur- face coat, which is a combination of resin and silicone powders, was ap- plied. Ten laminates of glass fibre were built up over the mould surface coat and further strength was achiev- ed by the addition of resin-bonded plywood, built up as a sandwich con- struction to a thickness of about 14 in. (32 mm.).

Steel angle irons were set into all window surrounds and mould edges and bonded in under six layers of glass fibre. Finally, 6 in. by 4 in. (15 cm. by 10 cm.) timber bearers were bonded to the back of the mould with glass fibre.

To complete the face mould, it was necessary to place into it the shape of the window reveals and piers. Ten separate mould sections were made, comprising four sides, three windows with lower panels attached, and three top panels. The face mould comprised 11 pieces. the bed of the mould carrying the face finish and all features of the front of the building; and the corner unit moulds

Far East Architect & Builder August, 1966

79

79