The original surface of the GRC can be subsequently treated to produce an even greater range of finishes. Surface finishes vary from very smooth and glossy to flat matt and a wide array of textured and patterned surfaces with or without pigments.
In addition to textures and patterns that are generated by spraying or casting into appropriate shaped moulds, sometimes with liners, surfaces of GRC / GFRC can also be treated chemically or mechanically, either when the product is freshly de-moulded or when it is already cured.
Water washing away a freshly set, but not yet fully hardened, cement paste is sometimes assisted by applying a coating of a retarder onto the mould surface prior to the facing mix being applied. In a typical treatment, the thin top layer is removed by a water jet or scrubbing to reveal a specially selected decorative fine aggregate (“exposed aggregate” process) on the external surface of a panel. This washing out by water is sometimes augmented by a treatment with a weak acid (usually hydrochloric) to dissolve the thin top layer of the cementitious paste.
Strong acids can also be applied to the demoulded surface to expose the decorative sand or fine aggregate. This is usually done immediately after demoulding, as the surface of the GRC / GFRC rapidly becomes impervious and difficult to penetrate.
Mechanical treatments aim to produce a surface with a texture simulating natural materials, such as either a rough, or polished, stone. This can be achieved by wire brushing, grit blasting or grinding / polishing at a suitably early age.
Surfaces of GRC / GFRC can be painted. The paint is often applied onto a pre-pigmented GRC / GFRC of a similar base colour (see also Colours). There are a number of suitable proprietary paints and penetrative stains now on the market which can be used to finish the appearance of a GRC / GFRC product.
Special surface finishes can also be created by using the GRC / GFRC as a substrate carrying an attached “veneer” of a decorative material, such as ceramic tile, sheets of terracotta, or slices of clay bricks, polished stone and similar materials.