Finishes

The range of finishes that can be produced on precast cladding can be summarized according to their method of production as:

- surfaces cast direct from the mould, e.g. smooth centre, board-marked concrete, grooved or serrated, including reconstructed stone finishes;

150 mm proprietary channel for adjustment parallel to edge

Packing for adjustment

150 mm proprietary channel for adjustment parallel to edge

Slotted hole for vertical adjustment

Packing for adjustment

1.32 Method of adjustment with cleat fixing offering movement in x, y and z axes.

- finishes in which the cement surface is removed to expose the aggregate in the concrete;

- applied finishes, such as tiles, stone facings and bricks;

- surfaces textured by tamping or shaping.

The various methods to produce these finishes are dealt with by Gage (I 974) in his guide to exposed concrete finishes. In addition, examples of various exposed aggregate finishes can be seen in Oram (1978). Most precast concrete cladding panels use such exposed aggregate finishes, and their colour and texture are largely affected by the type of aggregate used. The use of applied finishes affects the type of casting used (Fig. I. I 0).

Many buildings incorporate natural stone-faced cladding fixed with dowels or retention angles, and it is clear from examples of failures seen recently that there is a need to detail the fixings of stone panels to avoid spalling of the stone facing. Manufacturers normally advise the minimum thickness of limestone as 60 mm and of granite as 50 mm. Fixing dowels must not penetrate the stone to more than two-thirds of its thickness.

The incorporation of stone into curtain walling has promoted an interest in lightweight stone cladding consisting of a thin layer of natural stone (granite, marble or limestone) bonded to a unidirectional glass filament and phenolic resin skin bonded either side of an aluminium honeycomb core. Panels can be typically produced to a maximum size of 2400 mm x 1200 mm, 25 mm thick. Typical weight is 25 kg/m2 compared with 50 mm thick granite, which weighs I 35 kg/m2, and 60 mm thick limestone, 144 kg/m2.

1.33 Ribbed concrete panels.

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