Patio slabs sinking on gravel or chippings: what to do?

On balconies and flat roofs, concrete or stone slabs are often laid in a bed of gravel or chippings. Once that bed shifts under load, individual slabs sink and the surface becomes uneven. Before any refurbishment, the first decision is what happens to the existing slabs. Four approaches can be considered.

Relaying the old slabs involves the least work. They are lifted, the bed is raked level and the slabs are relaid. To hold the gravel or chippings in place, suitable gravel grids can be installed.

In the second approach, the old slabs stay where they are and serve as the base for the new patio surface. This requires the existing slab surface to be level or to be realigned as described above. Rubber granule patio tiles are suitable as the new surface. They add only about 2 to 3 cm in height and are water-permeable, so drainage works as before.

In the third approach, only the concrete or stone slabs are taken up and the bed stays in place. The rubber tiles are laid straight onto the bed once suitable gravel grids have stabilised it. The build-up height is adjusted with a thicker bed or with polystyrene boards laid on the bed. Where polystyrene boards are used to adjust the level, the surface must still be able to drain.

In the fourth approach, the entire old covering and the bed are removed. Depending on conditions on site, the rubber tiles can then be laid straight onto the existing waterproofing membrane. The waterproofing membrane can equally be renewed or insulation can be added, with the rubber tiles laid on top of that.