How to lay a patio: complete materials list
A patio is four layers, and each one has its own quantity to work out. Miss one and the job stops while you drive back to the merchant. Here is the full list for a typical 4m × 3m patio.
Layer 1 — the sub-base
Dig out to around 200mm and compact 100mm of MOT Type 1 for a foot-traffic patio (150mm if a car will ever cross it). At 2.1 t/m³, a 12m² patio needs 12 × 0.1 × 2.1 = 2.5 tonnes — three bulk bags.
Lay a weed membrane on the dug-out subsoil before the Type 1 goes down.
Layer 2 — the bedding
Slabs are bedded on a 40mm full mortar bed, mixed roughly 5 parts sharp sand to 1 part cement. For 12m² you need about 0.48m³ of bedding, which is around 0.8 tonnes of sharp sand and eight to ten 25kg bags of cement.
Never spot-bed slabs on five blobs of mortar. Voids underneath crack slabs and hold water that freezes in winter.
Layer 3 — the slabs
Work out slab numbers from the slab size and add 5% for cuts and breakages. 600 × 600mm slabs cover 0.36m² each, so 12m² needs 34 slabs including waste.
Lay to a fall of about 1 in 80 away from the house, and keep the finished surface at least 150mm below the damp-proof course.
Layer 4 — the joints
Brush-in jointing compound covers roughly 5–8m² per 20kg tub at a 10mm joint width, depending on slab size. Two tubs is usually right for a small patio. Alternatively point with a dry 4:1 sand and cement mix, but resin compounds are far quicker and far less likely to stain.
Sundries people forget
Edging or haunching for the open sides, a weed membrane roll, a sharp sand top-up, a bag of cement more than you think you need, and a skip for the spoil. Hire a plate compactor for the day — it costs less than the slabs you will crack without one.