Achieving good quality surface finishes
There are three main factors required to produce a good quality concrete surface:
1. The correct quality of concrete, which has been designed to achieve its ‘finishability’.
2. The use of the correct type and quality of form face material and release agent suitable for the finish specified.
3. Workmanship, both in producing the formwork and mixing, placing, compacting and finishing the concrete.
Most specifications and Bills of Quantities take into account the second requirement for the right quality of formwork. Generally there is a separate item in the Bill of Quantities for the formwork to produce specific finishes. Similarly, all experienced contractors and formwork sub-contractors are aware of the requirements for good workmanship in production of the formwork and the placing and compacting of the concrete. However, very few specifiers and formwork contractors seem to be aware that the concrete should not only have a characteristic strength as specified, but should be suitable to achieve the required finish. Visual concrete: design and construction and Concrete Advice No. 17, Achieving good quality as struck in situ concrete surface finishes, give guidance on suitable materials and mix proportions to achieve the required finish.