22 EXTERNAL WALL FINISHES
The versatility of architectural precast concrete
By Stephen Maddalena, Chairman of the Architectural Cladding Association
AS A RULE OF THUMB, CONCRETE THAT IS NEVER GOING TO BE SEEN ARRIVES ON SITE READY-MIXED WHEREAS CONCRETE THAT WILL BE PERMANENTLY ON VIEW IS GENERALLY PRECAST. CERTAINLY THIS IS SO FOR ARCHITECTURAL CLADDING, WHICH COULD BE DESCRIBED AS THE VERY ACCEPTABLE FACE OF MODERN ARCHITECTURE.
S
uch cladding can be found across a range of projects, from commercial and civic office schemes, residential, retail
and leisure developments, to hospitals and schools. The reason is not hard to find, for the direct and incidental advantages of precast cladding construction enhance quality and safety, improve efficiency and productivity, and help provide programme and price certainty. Furthermore, innovations in production methods combined with significant investment in labour and plant resources enable architectural precast concrete panels to be provided in an ever- widening range of finishes and facings, shapes and sizes to meet the needs and aspirations of the most ambitious architects.
Fresh concrete is an extremely mouldable material allowing complex shapes to be formed. Panels can economically incorporate cill, coping, soffit, window reveal and special sections, especially where repetitive. Large panels avoid the need for a secondary structure for vertical support and lateral restraint, and grid-width units can reduce mid-span loadings on the structural slab edge. In addition, reduced wall thicknesses with precast cladding panels can increase net lettable floor area.
Finishes range from lightly textured reconstructed stone and polished concrete to coarser washed exposed aggregate surfaces. Though it may take a little research, it is today possible to select aggregates and cements to suit colour preferences. At the same time, precasting allows natural stone, granite, brick and terracotta tile facings to be assembled with a reinforced concrete backing, a single panel perhaps incorporating more than a 1000 bricks.
The low-energy production of precast concrete also scores well in terms of sustainability. Its use produces negligible waste, just enough concrete being batched to fill available moulds at the factory.
And at the end of the economic life of a building, the precast panels may be refurbished for re-use or crushed as hardcore. Each stage of manufacture is inspected in accordance with an independently certified quality system, and finish and dimensional accuracy are checked before delivery. The rider, of course, is that these many advantages can be attained only by early involvement of the specialist precaster.
Produced in accordance with BS CP 8297:2000, precast concrete cladding can be expected to last considerably more than 60 years and generally with no need of maintenance. In addition, it is an inherent sound insulator, non-combustible and fire- resistant. Dense concrete is also air- and watertight, and insulation can readily be incorporated, achieving U-values of 0.30W/m2
the thermal mass of concrete serves to reduce peak heating and cooling loads.
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