Planning a patio or paved area

A patio looks like a flat surface, but it is mostly what is underneath: a compacted sub-base, a bedding layer and a fall that sends the water away. Slabs laid on a thin or soft base rock, sink and crack. Time spent on the levels and the sub-base is time not spent re-laying it.

This planner follows the order of work. The same steps cover a patio, a path and a base for a shed or a hot tub, with a thicker base for anything heavy.

Step 1: Decide the size, the position and the levels

Mark the area with pegs and string, and put your table and chairs inside it. Work out the finished level: it must stay at least 150 mm below the damp-proof course of the house, and fall away from the building so that rain runs off. A fall of about 1 in 80 (roughly 12 mm for every metre) is a common aim.

Step 2: Dig out and build the sub-base

Dig out to the depth of the slab, the bedding and the sub-base, remove topsoil and soft spots, and compact what is left. The sub-base is usually MOT Type 1 crushed stone, laid in layers and compacted with a plate compactor. A patio needs about 100 mm, and anything that carries vehicles needs more. Check for buried cables and pipes before you dig.

Step 3: Work out the whole shopping list

The patio calculator gives the slabs with an allowance for cuts, the sub-base, the sharp sand and cement for the bed, and the pointing mix. Slabs are sold by the pack or the pallet, so order a few spares from the same batch, since colours vary.

Step 4: Lay the slabs

Lay slabs on a full bed of mortar or on a bed of sharp sand with a mortar spot, working from a straight edge and checking the fall with a level and a spacer. Tap each slab down, keep the joints even, and cut the edge slabs last with a saw or a cutter. Lay on a dry day, and keep off the slabs while the mortar sets.

Step 5: Point, clean and seal

Fill the joints with a pointing mortar or a jointing compound, brush off the surplus before it sets, and clean the patio once the mortar has cured. A sealer is optional and helps against staining on porous slabs.

Before you start

• The finished level against the damp-proof course, and the fall away from the house.
• Planning rules in a conservation area or where the patio is in the front garden: paving more than 5 square metres of a front garden with a non-porous surface needs permission in England unless the water drains to a permeable area.
• Services under the ground, and the position of drains and manholes.
• Delivery and storage of heavy packs of slabs.
• A plate compactor and a slab cutter, hired for the weekend.

Mistakes that cost people money

• A sub-base that is too thin or not compacted, so the slabs sink and rock.
• Laying the patio too high, bridging the damp-proof course.
• No fall, so water pools against the house.
• Laying slabs on dabs of mortar with gaps underneath, which crack when stood on.
• Ordering exactly the area with no allowance for cuts.

Frequently asked questions