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A brushed finish is obtained by pulling a brush over the surface of the fresh concrete, after the surface has been levelled. The type of finish obtained will depend upon the coarseness of the brush bristles and the length and shape of the tufts. Coarse texture is given by stiff-bristled brooms, softer bristles giving medium and light textures. Brushes can have plastic bristles or steel tines of varying gauge and density. Normal manual sweeping brooms produce an unsatisfactory texture for finishing concrete surfaces and should not be used; rather, a purpose-made brush should be used. Such brushes generally have steel bristles or tines and long heads to reduce the number of passes.
A commonly used piece of equipment for producing a brush finish is the combined skip float and brush. In use, the skip float is pushed across the bay using the long handle. When the skip float has reached the bay edge the handle is turned which lifts the skip float and lowers the brush head onto the concrete. The brush is then drawn back across the bay. Care is needed with the timing of the use of this equipment. If it is used too early bleed water can be worked into the surface, thus weakening it, and pieces of coarse aggregate may be ‘plucked’ out of the surface by the brush.
Brushed finishes are suitable for areas trafficked either by vehicular or foot traffic and are also suitable for many types of mechanical handling plant. Brushing transverse to the direction of the traffic either by hand or machine using a stiff brush has been used widely. Its disadvantage is that it is difficult to control the frequency of the striations and the profile of the texture. Hand or mechanical brush finish usually gives striations which are 1.5–3mm deep.
Many of the above comments on the difficulty of obtaining a uniform finish apply particularly to brush finishes. Therefore it must be appreciated that the aesthetic appearance of a brushed finish on large areas may be disappointing.
The National Building Specification requires a brushed finish to produce a “lightly textured surface”. The Highways Agency Manual of contract documents for highway works requires the surface macro-texture to be measured using the volumetric patch technique described in BS EN 13036-1.
Brushed finishes are relatively shallow and may quickly wear away under service traffic.
Acknowledgement: The Concrete Society
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