Laying a Patio

A patio is a groundworks job wearing a decorative surface. The slabs everyone sees are the quick part; the dig, the sub-base and the falls underneath decide whether the patio is still flat and dry in ten years. Almost every patio failure (rocking slabs, pooling water, damp walls, frost-cracked corners) traces back to a shortcut below the surface.

This page is a working template for the whole job: the task order, what you will be ordering, the drainage and damp rules that apply, and the calculator that serves each step. The three decisions worth making before any digging: where the finished level sits relative to the house damp-proof course, which way the water falls, and where it goes when it gets there.

Work in this order

1. 1

   Plan the level, the fall and the drainage

   Three decisions come before any digging: the finished patio level must sit safely below the damp-proof course of the house, the surface must fall away from the building so rainwater drains, and the water must have somewhere acceptable to go. Get quantities early with the Patio Paving Calculator, and check for underground services near the house before committing to a dig line. The planning rules around impermeable surfaces and drainage are covered in our patio guide; permeable designs are quantified by the Permeable Paving Calculator.

2. 2

   Excavate for the full build-up

   The dig has to make room for the whole sandwich: sub-base, mortar bed and slab thickness, all below your finished level. Estimate the spoil volume and disposal with the Groundwork Excavation Calculator, and compact the exposed ground before anything goes on top of it.

3. 3

   Lay and compact the sub-base

   Type 1 MOT crushed stone goes down in layers, each compacted with a plate compactor: the sub-base carries the patio, and slabs laid on soil or bare sand sink and rock within a season. Tonnage and bulk bags come from the Type 1 Sub-Base Calculator.

4. 4

   Set the falls with lines and pegs

   String lines at finished slab height establish the fall away from the house before the first slab is bedded. Checking the gradient as you go is far easier than correcting it after the mortar has stiffened: our patio guide gives the fall to work to.

5. 5

   Bed each slab on a full mortar bed

   Slabs are laid on a full bed of sharp sand and cement mortar, not on dabs: dot-bedding leaves voids that fill with water and crack slabs in frost. Quantities for the bed come from the Paving Slab Calculator (it includes the sand and cement) or the Mortar Calculator. Work away from the house, keep the joints consistent, and check every slab against the line.

6. 6

   Cut the edges, then restrain them

   Edge slabs are cut with a diamond blade (eye, ear and dust protection on), and the perimeter is then locked in place: haunching mortar or a fixed edging stops the field of slabs creeping sideways over time. Edging options are quantified by the Garden Edging Calculator and Kerb Edging Calculator.

7. 7

   Joint, clean and let it cure

   Jointing waits until the bedding mortar has set, then the gaps are filled with a jointing compound or a dry sand and cement mix, and the faces are cleaned before anything stains. The patio then needs its cure time before furniture goes on. The full method, including timings, is in our step-by-step patio guide.

What you will be ordering

The heavy deliveries are Type 1 MOT crushed stone for the sub-base, sharp sand and cement for the bedding mortar, and the slabs themselves, ordered with a margin for cuts and breakages and from a single batch so the colour is consistent. Porcelain slabs need a priming slurry or specialist adhesive on top of the standard bed; natural stone and concrete lay on the traditional mortar bed.

The small items decide the finish: jointing compound or kiln-dried sand for the gaps, edging or haunching mortar for the perimeter, and an optional membrane on soft ground. Plate compactor hire is part of the real cost of the job. Each calculator above returns the order quantities for its own layer.

The rules that touch a patio

Every calculator, by job stage