How slip-resistant are water-permeable walkway slabs in the rain?

Water-permeable walkway slabs are slip-resistant in the rain, provided that their pores remain clear and the surface is free from deposits. Water-permeable walkway slabs made from PU-bound rubber granules achieve slip resistance rating R10 and drain rainwater through their porous structure. Slip resistance is measured to BS EN 16165 on an inclined plane using test footwear and a lubricant; depending on the range, the mean angle of acceptance is between 12 and 17 degrees. For dry conditions, classification DS is also declared to BS EN 14041.

Slip-resistant is the appropriate description, as no surface provides grip in every condition. The granular, open-pore surface creates traction because the shoe sole moulds around the individual granules and deforms as the wearer steps down; most friction results from this deformation. The rubber tile also yields, increasing the contact area between the shoe sole and the surface.

In rain, water permeability also supports traction. An accredited institute measured more than 1,100 litres per square metre per hour to BS EN 12616. Rainwater therefore does not remain on the tile surface: it passes through the rubber tiles and drains away through channels on their underside. As long as the pores are clear, no continuous water film forms between the shoe sole and the surface.

Deposits on the surface behave differently from ordinary wetness. Damp leaves, snow, ice and a thin algae film after a mild winter can sit between the shoe sole and the surface, preventing the structure of the rubber tile from engaging. Keeping the area clear of leaves, sweeping regularly and removing oil or grease promptly helps to maintain traction over the years.