How do I lay rubber tiles on stone chippings or gravel?

Rubber tiles can remain permanently level on stone chippings or gravel where the loose aggregate is first stabilised with plastic honeycomb grids. These honeycomb grids are also sold as gravel grids, lawn grids or gravel cells.

Within each cell, the stone chippings can no longer move. A typical stone chippings layer consists of particles of broadly uniform size and lacks the fine material that would fill the voids between them. Stone chippings therefore cannot be compacted effectively and remain mobile. This movement is of little consequence beneath a rigid concrete slab, but mobile stone chippings beneath a rubber tile can form hollows that show through on the tile surface.

Installation starts by removing the topsoil and trimming the substrate to formation level. A thin stone chippings layer is then spread over the formation level and levelled with particular care before the gravel grids are installed. Fill the grids precisely to their upper edge. Angular stone chippings are more suitable for filling than rounded gravel because the particles interlock more effectively. The rubber tiles are then laid on the filled gravel grids.

Where the substrate has limited bearing capacity, a compacted crushed-stone sub-base is installed beneath the stone chippings layer and compacted. The same sub-base is required where frost protection is needed.

WARCO approves only specified ranges with a flat underside for direct installation on a stone chippings bed without gravel grids. This method always requires a compacted crushed-stone sub-base. A mixture of crushed sand and stone chippings is levelled over the compacted sub-base and compacted with a plate compactor. Unlike stone chippings alone, this mixture contains fine sand and therefore becomes firm.

A layer below the minimum thickness cannot be levelled and compacted properly. A layer above the maximum thickness leaves too many loose stone chippings beneath the patio tiles. Under a three-metre straightedge, the final surface must have no more than the specified tolerance of clearance at any point.

Every step across stone chippings or gravel produces a crunching sound, and movement in the loose material can be felt underfoot. Beneath rubber tiles 2 to 5 cm thick, mobile stone chippings can form hollows that show through on the tile surface.

For this direct-lay construction, level a 2 to 3 cm laying course of crushed sand and stone chippings (0/5) over the compacted sub-base. A layer under 2 cm cannot be levelled and compacted properly; a layer over 3 cm leaves too many loose stone chippings beneath the patio tiles. Under a three-metre straightedge, the final surface must have no more than 0.5 centimetres of clearance at any point.