Off-form concrete elements are most commonly produced using grey cement. The high quality of the moulds and the quality assured manufacturing techniques used by National Precast Members mean that the quality of finish is extremely high and generally requires no additional finishes to be applied, other than perhaps stain or paint. For variation, false joints and rebates can be incorporated into designs, or alternately many precast manufacturers are able to include colour pigment into the concrete mix.
The Australian Standard AS3610.1 – 2010, Formwork for Concrete describes the benchmarks for off-form grey concrete. It defines in detail the characteristics of the classes of surface finish with Class 1 being the highest standard and Class 5 the lowest. Class 1 is only recommended for use in very special features of buildings of a monumental nature and must not be specified for whole elevations. Class 2 is the most common specification for high quality architectural precast concrete.
Whilst AS3610 can be used to evaluate the quality of surface and tonal colour range of grey concrete cast against the mould, the standard cannot be directly applied to trowelled surfaces, applied finishes or coloured concrete. For evaluation of these surfaces the Standard requires that samples of the finish and colour are made to manage the quality of finish and the acceptable variations in colour for the project.
For more information regarding this finish please refer to 10.6.2 of the Precast Concrete Handbook (click here to buy the Handbook), National Precaster Issue 56 or talk to one of our Members.