Can You Lay Paving Slabs on Soil?
No — paving slabs should never be laid directly on soil, which settles, holds water and moves with frost. The correct build-up is ~150mm excavation, compacted ground, at least 100mm of compacted MOT Type 1 sub-base and a full mortar bed. A sand-bed, cement-free variant exists for light-duty paths.
No — slabs laid directly onto soil will sink, rock and crack, usually within a season or two. Topsoil compresses under load, swells and shrinks with moisture, and heaves in frost; any slab on it follows. Every lasting patio sits on the same stack: excavated, compacted ground → at least 100mm of compacted MOT Type 1 sub-base → a full 30–50mm mortar bed → the slab.
The correct build-up, in one paragraph
Excavate about 150mm below finished level (deeper for driveways), removing all topsoil and roots. Compact the exposed subsoil. Lay MOT Type 1 in thin layers, plate-compacting each, to 100mm+ compacted depth. Bed each slab on a full semi-dry mortar bed (sharp sand:cement ≈ 4:1) — priming the back if the slab is porcelain — to a fall of at least 1:80, then fill the joints. Step-by-step detail: the full guide.
The no-cement version (light duty only)
For garden paths and stepping stones, slabs can be bedded on 25–30mm of screeded sharp sand over the same compacted sub-base, with kiln-dried sand joints. It's easier to relay but settles more and invites weeds — legitimate for foot-traffic paths, wrong for patios with furniture or any vehicle. It is still not "slabs on soil": the sub-base does the work.
Why the shortcuts fail
- Slabs straight on grass/soil: uneven sinking within months; trip hazards, ponding, frost cracking.
- Slabs on a thin sand layer over soil: the sand migrates into the soil and the slabs follow it down.
- Mortar dabs instead of a full bed: voids collapse, slabs rock and crack — the most common professional-looking failure.
Sizing the job
Use the coverage calculator for slab and pack quantities (it adds a cuts-and-breakage allowance), and see the Kandla Grey hub or the full range for slab options.
Common questions, answered straight
Can I lay paving slabs straight onto soil?
No — soil settles, holds water and moves with frost, so slabs on it sink and crack. Build up from compacted ground with at least 100mm of compacted MOT Type 1 and a full mortar bed.
Can you lay paving slabs on soil without cement?
For light-duty paths only: compacted sub-base, a 25–30mm screeded sharp-sand bed and kiln-dried sand joints. More settlement and weeds than a mortar bed — never for patios or vehicles.
What do you put under paving slabs?
From the bottom: firm compacted subsoil, at least 100mm of compacted MOT Type 1 sub-base, then a full 30–50mm semi-dry mortar bed (with a priming slurry on the slab back if it's porcelain).
How deep do you dig for a patio?
About 150mm below finished level for foot traffic — enough for the sub-base, mortar bed and slab — and 150–200mm of sub-base for driveways.
Pave Direct Ltd · Blue House Farm Yard, Deeping St Nicholas, PE11 3DH · 01778 343999