The natural riven surface is the peculiarity of Trentino stratified porphyry and is considered the added value of this stone, as the absence of surface transformations allows to keep the natural chromatic prerogatives of the stone completely unaltered as it was excavated from the quarry face. It also allows to retain the natural roughness with excellent anti-slip properties.
Therefore, the minimal, but inevitable irregularities present on the walking surface, are however perfectly compatible for use in outdoor pedestrian and vehicular environments, as recognized by the EN 1341: 2012 standard. In facts, the EN standard contemplates at point 3.14 the natural riven porphyry as a HEWN FINISH surface, because it is obtained by splitting or flaking action with all the relative tolerances of the case.
The hewn finish of the natural quarry top should not be confused with other artificially obtained finishes such as sandblasted and flamed (coarse textured) or polished (fine textured) surfaces.
Furthermore, as stated in point 4.6.1 of EN 1341: 2012, the hewn finish (natural quarry surface) is considered capable of guaranteeing a satisfactory degree of anti-slip without having to verify the circumstance through the specific test method adopted for the other superficial finishes.
Below are the above-mentioned extracts of EN 1341: 2012 as follows: