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 that has no lateral restraint is not sufficiently stable beneath the surfacing. A suitable base is formed with gravel stabilisation grids, also known as gravel grids. With these components, the area is divided into many small cells in which the filled angular aggregate is restrained from moving sideways or being washed out during heavy rain. The tiled surface can therefore remain level over time.
Without cellular confinement, loose grains move sideways when pressure is applied. Water entering the layer can wash out fines and carry loose aggregate away, leaving voids beneath the surface. Because an elastic tile follows the depression below, its centre can subside while its edges curl upwards.
An existing loose layer of gravel or chippings does not provide a sound formation. Angular crushed aggregate may be screeded to the required profile and compacted, but rounded aggregate must be removed. Sand must be excavated until firm ground is reached. In a former loose-fill sand play area, excavation may extend several spade depths. A crushed stone sub-base is then built up and compacted in layers to formation level.
The gravel stabilisation grids are laid at formation level or bedded into a layer of angular aggregate. Where 4 cm anchoring spikes project from the underside, this layer must be at least 6 cm deep, allowing the spikes to be fully embedded and the grids to rest evenly. Angular crushed aggregate is used for the fill because the particles interlock within the cells, whereas rounded particles remain mobile. The fill is brushed into the cells, mechanically compacted, topped up and screeded flush with the upper edges of the grids. The result is even bearing beneath the entire tile area rather than contact only along the grid ribs.
The safety tiles are laid in accordance with the relevant installation instructions. The product range determines whether edge restraint is needed. Certain ranges are also approved for laying over a thin layer of angular aggregate. Both points are specified for each product on the WARCO website.