How do I lay rubber tiles on grit or gravel?

Rubber tiles can be laid so that they remain level on grit or gravel where the loose aggregate is stabilised beforehand with plastic cellular grids. These grids are also sold as gravel grids, lawn grids or gravel cells. Within each cell, the grit can no longer migrate.

In a typical grit layer, the particles are broadly the same size and there are no fines to fill the voids. Grit cannot be compacted effectively and remains mobile. Beneath a rigid concrete slab, this movement is of little consequence. Beneath a rubber tile, however, mobile grit creates depressions in the tile surface.

Installation starts with removing the topsoil and grading the substrate to formation level. A thin layer of grit is then spread and screeded with great care, followed by the cellular grids. The grids are filled flush with their upper edges. Crushed grit is more suitable for filling than rounded gravel because it interlocks more effectively. The rubber tiles are then laid over the filled grids.

Where the substrate has limited bearing capacity, or where frost protection is required, a compacted crushed-stone sub-base is installed beneath the grit layer. Only specified ranges of rubber tiles with a flat underside are approved for direct installation on a grit bed without gravel grids. A compacted crushed-stone sub-base is always required for this method.

A mixture of crushed sand and grit is spread over the compacted crushed-stone sub-base and compacted with a plate compactor. Unlike grit alone, this mixture contains fine sand and therefore becomes firm. A layer below the minimum thickness cannot be screeded and compacted properly, while a layer above the maximum thickness leaves too much loose grit beneath the rubber patio slabs. Finally, the gap beneath a three-metre straightedge must not exceed the stated tolerance.

Grit or gravel crunches underfoot, and the movement of the loose aggregate can be felt with every step. Beneath a 2 to 5 cm thick rubber tile, mobile grit creates depressions in the tile surface.

Over the compacted crushed-stone sub-base, spread a 2 to 3 cm layer of crushed sand and grit (0/5). A layer under 2 cm cannot be screeded and compacted properly. A layer over 3 cm contains too much loose grit beneath the rubber patio slabs. Finally, there must be no more than 0.5 centimetres of clearance beneath a three-metre straightedge at any point.