Why do safety tiles and rubber patio tiles sit more evenly on gravel stabilisation grids?

Safety tiles and rubber patio tiles sit more evenly on gravel stabilisation grids because the layer of angular grit is confined within individual cells. Once enclosed, the grains cannot migrate sideways under load or be washed out during heavy rain. The bedding beneath the tiled area therefore remains more stable over the years.

A loose bed of crushed, angular grit is usually single sized, with few or no fines to fill the voids between the grains. It can therefore remain mobile even after compaction. This movement does not affect the seating of a rigid concrete slab, but elastic safety tiles and rubber patio tiles made from rubber granules distribute imposed loads less evenly across the sub-base. Grit may gradually be displaced towards the tile edges. Bearing is then lost beneath the centre, which can settle, while the displaced grains accumulate under the perimeter and raise the edges. The result is a tile with a sunken centre and upturned edges.

With gravel stabilisation grids in place, the loose grit is divided into small compartments and forms a stable sub-base. These components are also described as gravel grids, grass grids or plastic honeycomb grids. Every cell is filled flush with its upper edge, so the enclosed grains remain in position under load and during heavy rain. The stated load capacity of the filled grids is up to 400 t/m². The completed area remains permeable to water, and where the ground allows rainfall to soak away, a fall and separate drainage are usually unnecessary.

Ground preparation can also be reduced where the soil is firm and the area is only lightly used. Once the topsoil has been removed, the grids can be placed on a thin levelling bed of angular grit. This requires less excavation than a conventional construction. A sub-base of compacted crushed stone is only required where the ground is weak, a frost-resistant build-up is needed or the area will be exposed to higher imposed loads.