About natural stone

For flooring, especially in public spaces, 2 selection criteria are essential: slip resistance and abrasion (“wear”) resistance.

Slip resistance is measured using the friction coefficient, which depends on the type of stone, the finish, moisture on the surface, and installation. There are also factors that affect slipperiness independent of the flooring itself (walking speed, traffic level, the material on the sole of footwear). Today there’s a unification of concepts, with the stone industry adopting ceramic tile standards. Under the DIN 51130 standard, the following slip-resistance classes are defined:

R9 (slip angle 6°-10°): entrances and stairs accessed from outside; restaurants; shops; clinics; hospitals; schools.

R10 (10°-19°): shared restrooms and showers; small kitchens in restaurants and cafés; garages and basements.

R11 (19°-27°): food production facilities; medium-sized restaurant and café kitchens; work environments with lots of water and sludge; laboratories; laundries; hangars.

R12 (27°-35°): production facilities for fat-rich foods (dairy products, cooking oils, meat); large kitchens; industrial areas with slippery substances.

R13 (>35°): where large amounts of grease are used; food processing areas.

Slip resistance for barefoot areas is divided into categories A through C.

A – dry areas (walking barefoot, changing rooms).

B – showers, bathrooms, pool surrounds, children’s pools, shallow pool floors.

C – pool entry areas, swimming lane slopes.

In the natural stone industry, slip resistance is measured using the friction coefficient (traditionally static, now more commonly dynamic). A dynamic friction coefficient of 1 indicates a slip-resistant surface, while 0 indicates a very slippery surface. Recommendations tend to apply: in semi-damp areas (kitchens), the coefficient should be around 0.6, and the same for outdoor surfaces. A coefficient between 0.3-0.6 (for dry, clean surfaces) indicates a sufficiently low level of slipperiness.

What really matters is how slip resistance is improved. For granite, flaming the tiles is common practice. Brushing travertine or marble surfaces increases friction. All mechanical surface treatments (bush-hammering, sandblasting, etc.) improve underfoot safety. Anti-slip chemical treatments (e.g. chemical sandblasting) are also effective. Balancing the need for walking safety against maintenance costs makes choosing stone for exterior and wet-area flooring an ongoing challenge.