Visual concrete is once again being appreciated and used
expressively by architects. Partly this is due to the wish to use
the thermal mass of concrete in buildings
to reduce the heating and cooling loads. The latest version of the
National Structural Concrete Specification
(NSCS) from Construct, the concrete frame contractors’ trade
association, now makes the specification of visual concrete much
easier. The previous specifications found in BS 8110 have now been
replaced by four different classes of formed finish: basic,
ordinary, plain and special. Normally either ‘plain’ finish or
‘special’ finish should be used for concrete which is to be visible
during the lifetime of the building.
A plain finish is for use where visual quality is of some
importance such as areas occasionally seen or to be directly
painted. Joints between formwork panels will show and the step may
be up to 3mm. Tie-bolt holes should ideally be recessed and panels
and bolt holes should be in a regular pattern. The colour might
change with the concrete delivered and the re-use of the forming
material. A project example should be produced as one of the first
areas of concrete poured on the project and used as the benchmark
for the rest of the concrete.
To achieve visual concrete, a special finish should be specified
where the visual quality is of great importance. Sample panels
should be specified using the formwork system, the concrete and the
typical reinforcement to be used on the project for producing the
particular finish. The size and complexity of the sample should be
agreed to test the project detail and confirm that the execution
can produce the finish on a repetitive basis.
Where a project example or a sample panel is specified, the
viewing distance should also be agreed. The normal viewing distance
is assumed as 3m. The appearance of concrete is affected by the
concrete mix, the formwork and the workmanship on site.
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How to Achieve Visual Concrete
Concrete Structures 10