How should slabs and paving blocks be laid on soil?

Patio slabs, paving slabs and paving blocks must not be laid directly on undisturbed or made-up soil. Each requires a laying course.

Topsoil is not load-bearing. Cohesive soil can heave in frost, causing laid slabs and paving blocks to settle or lift unevenly. This applies to both natural ground and made-up ground.

Topsoil is removed, then the ground is trimmed to the formation level and compacted. Fill is placed and compacted in layers. The required thickness of the sub-base depends on the intended use, the soil type and frost conditions at the site. A garden walkway carries less load than a driveway, and a sub-base on cohesive soil is made thicker than one on sandy soil. For frost protection, the total build-up thickness from the surface to the formation level is decisive.

Resilient slabs are not normally laid on a loose bed of sand, grit or gravel. They are generally laid on plastic gravel grids, also sold as lawn grids or gravel honeycombs. Gravel grids should be filled with grit to their upper edge and screeded level.

On load-bearing, non-frost-susceptible ground and under light loading, gravel honeycombs are laid on a carefully prepared formation level with a 2 to 5 cm thick, smooth-screeded grit laying course. On unfavourable ground or where loads are high, an additional compacted crushed-stone sub-base is placed on the formation level beneath the laying course and compacted in layers.

Paving blocks and rubber tiles with plug-in connectors require edge restraint.