What goes under patio slabs and what sub-base is needed?

Patio slabs may be made from concrete, natural stone, wood, plastic or rubber granules. An even, firm and frost-resistant sub-base is required beneath every type. How much preparation is needed depends on whether the slabs are rigid or elastic and whether the patio already has a hard surface.

Rigid paving slabs made from concrete, natural stone or porcelain are heavy and liable to crack where support is uneven. They are laid on a levelled laying course of grit over a compacted sub-base, fixed with tile adhesive to a concrete base or set on adjustable pedestals. Decking boards and interlocking composite decking tiles are installed on decking joists or adjustable pedestals.

Rubber paving slabs made from PU-bound rubber granules are elastic and do not break. Deflection can occur over individual adjustable pedestals, so continuous support is required. On a patio already surfaced with concrete, asphalt, block paving or natural stone paving, the slabs can be laid loose without a mortar bed, tile adhesive or jointing compound.

If no such hard surface exists, a sub-base of gravel grids, also known as grass grids, is installed beneath the rubber slabs. The cells are filled right to the top with grit. The result is an even, water-permeable support for the patio slabs. No concrete is needed.