March 31, 2006 | Recommend this Article »

Stone finishes

Stone lives through its haptic. Customers not only want to see a stone, but also touch it – important to know when it comes to marketing finishes.

Whether a stone appears hard or soft is not just a question of petrography. Marble can feel hard, granite silky matt – depending on how the surface has been finished. Almost anything is possible. Coarsely honed or jet-blasted, highly polished or roughened with a microfine finish by a laser beam. The decisive factor is what the stone is to be used for and the visual impact it is to create.

Apart from polished surfaces, marks from the finishing process are now en vogue again. This makes every slab unique. A structured surface shows that the material does not end on the surface, but has depth; in other words, it is matter and not just decoration.

Traditional processing techniques like honing or bush-hammering are still available, but the surface relief is very rough and is mainly suitable for accentuating walls. Honed or bush-hammered floors are non-slip, but difficult to clean. Artificially aged “antiqued” stones are an alternative. The slabs are sanded in a rotating drum by adding quartz or coarse ballast. Distressed edges improve the rustic look. A final coating of wax restores the colour of the material.

Grinding is one of the most frequently used processes. Despite modern machines and abrasives, there is still no standard or simple test facility for surface roughness. Ground surfaces always show grinding marks under opposing light conditions, also differences in gloss depending on mineral content and distribution.
The most attractive side of a natural stone is the polished surface, which brings to light the whole variety of colours and structure. Normally, the surface is polished to such an extent that no more grinding marks are visible. The advantage of the polished surface apart from the appearance is the best possible cleaning, but the necessary non-slip properties are not achieved.

One of the most common forms of finishing hard stones containing quartz is flaming. The flamed surface has particularly good non-slip properties, but is difficult to clean, especially indoors. Not every stone is suitable for flaming and colour changes may occur, depending on material. Yellow granites change to a reddish colour, others turn yellow or grey. To roughen up the surface without changing the colour, stones susceptible to colour changes are blasted using a water jet. The resulting appearance is not comparable with any traditional finishing process. The surface structure varies according to water pressure and throughput speed.

Brushed surfaces are currently experiencing a boom as an alternative to grinding. The surface has a soft velvet touch. Depending on the process, the gloss effects and visual properties are just as variable as grinding. Brushing is often preceded by a coarser finishing process such as flaming. After the coarse roughing, the rough layer is smoothed using brushes with metal or plastic bristles containing abrasive grains. The brushes can be mounted on conventional production plants. The advantage is a soft, living surface structure that is easier to clean than flamed surfaces.