Crystal cement granite (in Dutch kristal-cement-graniet, or kcg) is a thick, cement-bound bonding layer sprayed onto the substrate, into which granules of granite, basalt or glass are then applied while it is still wet. The result is a rough, decorative-render-like finish in which the aggregate sets the appearance.
It is not a brand name but a technique: a surface finish applied mainly to concrete.
Where it is used
The technique is found mostly on facades, viaducts and bridges. The reason is practical: bare concrete surfaces in infrastructure show every stain and every repair, and need maintenance. An aggregate finish hides that patchiness and gives the designer freedom in colour, grain and pattern.
What it offers
- Design freedom — the colour of the cement layer and the type, colour and coarseness of the aggregate can be combined; patterns and panel divisions are possible too.
- Low maintenance — a mineral, cement-bound finish on concrete is durable and generally needs little upkeep.
- Hides irregularities — minor unevenness, pour lines and colour differences in the concrete disappear under the texture.
Points to watch
- The substrate decides the result. The concrete must be clean, sound and rough enough. Laitance, mould oil and loose material have to come off, usually by blasting or high-pressure washing. A layer over a contaminated substrate will let go sooner or later.
- Weather. As with all cement-bound finishes: do not apply in frost or in full sun, and cure it so the layer does not dry out too quickly.
- It is a spray technique. The work needs equipment and experience; it is not a DIY job. Work in areas that can be finished in one go, because a break in the surface stays visible.
- Soiling. A rough, granular surface collects more dust, algae and moss than a smooth one — particularly on north elevations and where water runs down the face.
- Repairs. A local repair always shows, however well it is done. Decide at design stage where joints and panel edges sensibly fall.
Related terms
- Facade finish
- Decorative render
- Exposed aggregate concrete
- Aggregate
- Concrete
- Scraped render
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