Why do playground safety tiles sit more evenly on gravel grids than on grit?

Playground safety tiles sit more evenly and remain stable for longer on gravel grids than on a loose grit bed. The honeycomb cells hold the aggregate in place, with the material contained within each individual cell. It can neither move sideways under load nor be washed out during heavy rain, so the tiled surface remains stable and safe over the years.

In a loose grit bed, the particles are broadly the same size and lack the fine material that would fill the voids. Even after compaction, the grit remains mobile. This movement is irrelevant beneath a rigid concrete slab, but an elastic playground safety tile or patio tile made from rubber granules does not spread loads evenly through the substrate. Over time, the grit may be pushed towards the tile edges. The rubber tile then loses support in the centre and sinks there, while displaced grit accumulates beneath the edges and lifts them. This pattern of damage is known as dishing.

Gravel grids are also sold as grass grids, gravel cells or plastic honeycomb grids. They turn a loose grit bed into a stable sub-base. When filling the cells, the aggregate is levelled exactly to the top edge. The contained material stays in place under load and in rain, leaving the tiled surface stable and safe. Filled grids can support up to 400 t/m², while the whole area remains water-permeable. Where the ground is permeable, a gradient and drainage are usually unnecessary.

On load-bearing ground subject to low loads, it is sufficient to remove the topsoil and lay the grids on a thin levelling layer of grit. Less excavation is required than for a conventional construction method. A sub-base of compacted crushed stone is only needed where the ground has limited load-bearing capacity, where the construction needs to be frost-proof, or where the area must carry higher loads. This limited amount of work is an argument in favour of gravel grids.