Why are playground safety mats or terrace slabs better installed on grass grids or gravel grids rather than on gravel?

Whenever rubber playground tiles or terrace slabs made of rubber granulate are to be permanently installed on natural or filled ground – for example, on a lawn, in a park, on a playground, or in an equestrian arena – using grass grids or gravel grids made from recycled plastic provides the most optimal and cost-effective base.

Grass grids or gravel grids used as a support layer offer only advantages compared to a conventional bedding of gravel (sand or small stones):

- In many cases, an additional sub-base of crushed stone can be omitted.

- The earthworks are often significantly reduced, with much less excavation required.

- Mechanical compaction is usually unnecessary.

- Generally, no slope or drainage is needed, as the entire surface is permeable.

- Playground safety mats or terrace slabs lie much better without the risk of depressions forming.

For any type of surface, including rubber granulate tiles, the supporting layer must be capable of permanently carrying the loads generated during use without deforming or settling. It is evident that the load on a terrace is lower than on a driveway.

In addition to the expected surface load, the nature and composition of the underlying soil play an important role. Less stable soils (for example, loose or cohesive soils) require a more robust support layer than stable soils with a low fine-grain content.

The appropriate construction of the support layer beneath the slab surface always depends on the local conditions. When using grass grids or gravel grids, three installation methods are possible:

A – Direct installation on the prepared ground:

In particularly good soil conditions and with low surface loads, it is sufficient to remove the topsoil (4 cm for the grid plus the height of the rubber tiles), carefully level the area, lay the grass or gravel grid on the leveled surface, and fill it up to the top edge with paving gravel or similar material. The tiles are then laid on top of the grid.

B – Installation in a gravel bed without an additional support layer:

Under good soil conditions and with low to moderate surface loads, it is sufficient to install the grid into a gravel bed. First, the topsoil is removed – 2–5 cm for the gravel layer plus 4 cm for the grid plus the height of the tile surface. The area is then carefully leveled. The crushed stone layer is compacted and smoothed on the levelled surface. The grid is laid on the gravel layer and filled up to the top edge, but not beyond, before the slabs are installed.

C – Installation on a gravel sub-base with a gravel topping:

In cases of unfavorable soil conditions, frost protection requirements, or high loads (e.g. vehicular traffic), a conventional sub-base of crushed stone should be installed. The thickness of the crushed stone layer after machine compaction is 10 to 40 cm, depending on the local conditions. During excavation, the following layer thicknesses must be considered: 10–40 cm of crushed stone, 3–5 cm of gravel, 4 cm for the grid, and the tile surface on top.

After excavation, the area is leveled, the crushed stone sub-base is carefully installed and mechanically well compacted, and a 4–6 cm layer of gravel is applied. The grid is then laid on the gravel bed and filled up to the top edge, but not beyond, before the surface is installed.

The major advantages of using grass grids or gravel grids are:

- A load-stable and firm support capable of handling up to 400 t/m².

- The entire surface is highly permeable and facilitates water infiltration.

- The gravel remains securely in the grid, preventing displacement or floating.

- Playground safety mats or terrace slabs remain level and secure for many years without the risk of depression formation.