How to Lay a Patio

What you need

Slabs, a sub-base of crushed stone, sharp sand or mortar for bedding, a spade and wheelbarrow, a tape measure, string lines and pegs, a spirit level, a rubber mallet, a plate compactor (hired for the day) and knee pads.

Step 1 — Set out and dig

Mark the patio's outline with pegs and string, and check the diagonals are equal so it is square. Dig out to the depth of the sub-base plus the bedding plus the slab thickness — typically 100 mm of sub-base, a 50 mm bedding layer and the slab on top. Slope the finished patio gently away from the house (about 1 in 60) so rain runs off.

Step 2 — Sub-base and bedding

Spread the sub-base and compact it in layers — a plate compactor is worth hiring. Then spread the bedding: a full mortar bed for heavy slabs, or a sharp-sand bed for lighter ones. Screed it level with a straight edge. The paving calculator gives you the bedding volume along with the slab count, so you can order both at once.

Step 3 — Lay the slabs

Start from a straight edge — the house wall or a string line — and lay the slabs with even joints, tapping each one level with a rubber mallet. Check the level across several slabs, not just one: a single level slab in a wavy patio is still a wavy patio. Work outwards and cut the edge slabs last.

Step 4 — Joint and finish

Brush jointing sand or mortar into the joints and compact the whole patio lightly so the slabs settle. Keep off it until the joints have set, and do not wash it down with a pressure washer in the first few weeks.

Worked example

A patio 10 ft × 8 ft is 80 ft² (7.43 m²). With 24 × 24 in slabs, 3 mm joints and 10% wastage, that is 22 slabs. The bedding for the same patio — 2 in deep — is 13.33 ft³ (0.49 yd³, or 0.38 m³). Those are exactly the numbers the paving calculator gives you.

Common mistakes

• Skipping the sub-base. Slabs laid on bare soil sink within a season. A compacted sub-base is not optional.
• No fall away from the house. A flat patio ponds water against the wall. Slope it gently away — about 1 in 60.
• Uneven joints. Joints that wander make the whole patio look crooked. Use spacers or a consistent gap and check the line as you go.

Safety

Check for underground utilities before you dig — in the US call 811, in the UK use LinesearchbeforeUdig. Slabs are heavy: lift with your knees, work in pairs, and wear steel-toe boots. Cutting slabs makes fine dust — wear a dust mask and eye protection, and keep others clear.

Try these calculators

• Paving Calculator — slabs and bedding for any patio.
• Sand Calculator — sand volume and weight for the bedding.
• Gravel Calculator — volume and weight for the sub-base.