The satisfactory production of large areas of smooth concrete is difficult due to variations in colour and the inevitability of some surface blemishes, which can be improved, but not eradicated by remedial work. Externally smooth concrete weathers unevenly due to the build-up of dirt deposits and the flow of rainwater. Therefore, if concrete is to be used externally as a visual
material, early design considerations must be given to the use of textured or profiled surfaces to control the flow of rainwater. Generally the range of finishes and quality control offered by precasting techniques is wider than that available for in-situ work, but frequently construction may involve both techniques. The use of external renderings offers an alternative range of finishes for concrete and other substrates. Figure 3.17 illustrates the range of processes available in the production of visual concrete.
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