How do I lay rubber tiles on grit or gravel?

Rubber tiles keep a level surface on grit or gravel over the years when the loose fill underneath is stabilised with plastic honeycomb panels, known as a gravel stabilisation grid or a gravel grid. The grit inside the individual cells can no longer travel.

The reason lies in the grit itself. In loose grit every grain is roughly the same size, and the fine grain that would fill the gaps is missing. Grit therefore stays mobile even after compaction, and it is pushed aside by every footstep. Beneath a rigid concrete flag such a hollow is still bridged, whereas under a rubber tile 2 to 5 cm thick it works its way right through to the surface.

The build-up begins once the topsoil has been stripped. The ground below is trimmed to formation level and compacted, and a thin laying course of grit follows, which only evens out the height differences that remain. The grid is then set out and filled to the top edge of the cells, no higher. Angular grit works better as a filling than rounded gravel, because it interlocks. The rubber tiles are laid loose on top.

Where the natural ground has little bearing capacity, or where the build-up has to be frost resistant, a sub-base of compacted crushed stone is placed and compacted beneath the laying course.

For laying straight onto grit without a gravel grid, WARCO approves only the ranges that have a flat underside. A compacted sub-base of crushed stone is needed in every such case, and a crushed 0/5 mix that runs from angular grit down to dust is screeded over it 2 to 3 cm thick and compacted with a plate compactor. Unlike grit on its own, that mix carries fine sand, which is what makes it set firm. Anything under 2 cm can no longer be screeded cleanly or compacted, and anything over 3 cm leaves too much loose grit beneath the tiles. A check with a 3 m straightedge at the end should find no gap over 0.5 cm anywhere, because nothing can be put right once the tiles are down.