How should safety tiles be laid on sand, gravel or chippings?
Safety tiles must not be laid directly on sand, gravel or chippings; loose aggregate alone does not provide sufficient positional stability beneath elastic safety tiles.
To restrain this loose aggregate, plastic honeycomb grids are used. These are also known as gravel grids, grass grids or ground grids. The grids divide the area into many small cells, which hold the infill material laterally in place and protect it from shifting or being washed away. This creates a permanently stable, level and water-permeable sub-base for safety tiles.
Without these cells, sand, gravel and chippings remain mobile under load. Over time, the strongly profiled underside of the safety tiles can press into the loose aggregate, moving material from the centre of a tile towards its edges. Depressions then form in the bedding, which the elastic safety tile follows: it may settle in the centre and lift at the edges. This deformation is known as dishing or cupping.
To avoid such settlement, a level formation with adequate bearing capacity must first be prepared. Unsuitable or easily deformable soil layers must be excavated to the depth required by the local ground conditions and the intended load, particularly where loose-fill impact-attenuating sand is present. Where the ground has low bearing capacity or is cohesive or frost-susceptible, the excavation is backfilled in layers with suitable crushed stone and carefully compacted. Where the ground is stable and loading is low to moderate, an additional crushed-stone sub-base may not be necessary, depending on the installation conditions.
On the prepared formation, gravel grids are laid either directly or on a thin, levelled layer of chippings, according to the substrate. The thickness of the chippings layer depends on the selected construction and local conditions. The ground spikes on the underside of the grids are approximately four centimetres long; they engage with the underlying layer and support the anchoring of the grids. A general minimum chippings-layer thickness of 6 cm is not required.
The grid cells are then filled to their upper edge with suitable chippings or gravel. Crushed, angular aggregate is beneficial because it interlocks well. The infill material is carefully brushed into the cells, topped up where necessary and levelled flush with the grid surface. The safety tiles then rest across the filled honeycomb structure rather than only on the grid ribs, creating a stable and water-permeable sub-base.
On this completed grid, the safety tiles are laid and connected in accordance with the relevant installation instructions. Whether edge restraint is required depends on the product range, the connection system and the installation conditions. Some WARCO products are specifically approved for installation on a thin layer of chippings.