Concrete finishes – general
A great variety of colours, textures and finishes can be obtained from in situ or precast concrete. The finished profile is an exact reflection of the surface of the mould. The casting process produces laitance, the very thin layer of fine aggregate and cement particles that migrate to the surface of the unit during casting, and masks the underlying aggregate/cement matrix. Various techniques are used to remove the laitance to expose the aggregate in its natural state or change the appearance physically by abrading or fracturing the surface. Within each technique the degree of exposure can be varied, with the result that a considerable variety of effects can be achieved, some of which are more suitable for precast than for in situ concrete. Various preparation techniques are described in separate entries, see Acid etch finish, Retarded surface finish, Grit blasted surface finish, Tooled surface finish and Polished surface finish.
There is always a risk that removing the laitance from the surface of the concrete may expose previously unseen blemishes, cracks or colour variations. Texturing of concrete should therefore only be performed on good quality fully compacted concrete.