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The production of a good quality ‘as struck’ finish is not an easy task and one of the biggest problems is the subjective interpretation of a written specification. An added complication is the differences between the various specifications in common use in the UK, see Plain formed concrete finishes. Certain blemishes (see separate entry Defects and deterioration) such as blow-holes and colour variation are inherent in concrete although they may be reduced by use of the correct type of formwork, release agent, concrete, and good workmanship, but will not be totally eliminated. Other blemishes are avoidable and can be eliminated by the use of the correct form face material, release agent, concrete mix and good workmanship. The perception of features and characteristics of surfaces depends, to a large extent, on the distance from which they may be seen. For example, small blow-holes may not be noticeable from much more than 3 m away. On the other hand, colour differences will be noticeable from afar. The sensible approach is to assess the quality of the surface at the distance from which it will be most frequently seen. It should be noted that lighting can have an important effect on the appearance of surfaces.
Concrete Advice No. 16, Assessing as struck in situ concrete surface finishes, gives further information.
For advice on achieving good quality finishes see separate entry.
Acknowledgement: The Concrete Society
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