How to Lay a Patio

Plan, measure and set the fall

Set out the patio area with pegs and string. Drive the pegs at the corners and the edges, then run string lines across the area to mark the finished patio level — remember to allow a 17mm-per-metre fall (1:60) running away from the house. Lay the strings first; everything else follows them.

Think about how the patio drains before you dig. The fall should carry water off the surface onto a lawn, a soakaway, or a slot drain — never back towards a wall or building. If the area is larger than about 25m², plan for a channel drain or two along the fall line so a heavy downpour doesn't pool.

Use a long spirit level to check the fall across the strings before any digging. The slope won't be visible by eye, but if you are off by 5mm at the high end you are 100mm off at 6m — too steep and water will run too fast, too shallow and water will pool.

Excavate the area

Strip the topsoil to the depth required for your build. The total excavation equals the slab thickness plus bedding sand (25–50mm) plus sub-base (100–150mm). For a typical 32mm concrete flag you'll be digging down roughly 175mm below finished level.

Mark it out twice, dig once. Use spray paint or a sharp spade to mark the finished patio height on surrounding walls or posts so you can see how deep you need to go as you dig.

Keep the base flat and firm. Remove any soft spots and backfill them with compacted sub-base. If you have tree roots in the way, dig around them rather than chopping through them — paving close to a tree often needs a root-protection membrane and a deeper, lean-mix sub-base.

Lay and compact the sub-base

MOT Type 1 is the standard sub-base for a domestic patio — a graded crushed stone that locks together when compacted. For a permeable build, use MOT Type 3 (open-graded) over a geotextile membrane so water drains through.

Spread the sub-base in two or three layers — never all at once — and compact each layer with a plate compactor. A 50mm-thick layer of uncompacted Type 1 will compact down to roughly 35–40mm; lay your layers that thick and you'll hit the right finished depth.

Hire a plate compactor for a day. Hand-tamping a patio sub-base is the slowest way to a problem patio.

Stop compacting when the surface is firm underfoot and rings with a solid thud rather than a dull thud when you tap it. Loose, soft sub-base is the leading cause of paving sinking within a year.

Add the bedding layer

Two main options, depending on what you're laying:

• Sharp sand only (dry laying) — for concrete flags of uniform thickness. Lay 25–40mm of sharp sand, screed it level with a timber straight-edge, then bed the slabs directly.
• Mortar bed (wet laying) — for natural stone of varying thickness or large-format flags. A 5:1 sharp-sand-cement mix gives a stiff, workable bed that won't squash underfoot. Lay it slightly proud and tap each slab into the final level.

Only screed as much bedding as you can pave before it dries or gets disturbed — about 3–4m² at a time on a hot day. Walking on a screeded bed leaves footprints that show through the finished patio.

Lay the slabs

Start in a corner — usually against the house or a fixed edge — and work outwards. Lay each slab onto the bedding with a 10–15mm joint between flags (use plastic spacers for consistency) and tap it down with a rubber mallet. Check the level and the fall every slab.

Tip: Dry-lay the first row along the longest straight edge before you mortar anything. It is much easier to correct the layout with no mortar in the way.

Cut slabs with an angle grinder and a diamond blade, or hire a block splitter for thicker flags. For curves, mark the cut with a flexi-curve or a piece of hose laid on the slab, then cut to the line. Wear eye and ear protection when cutting.

Lay the patio in even rows, working from the finished surface back towards the bedding — never step on freshly laid flags. If you do need to access a finished area, lay planks down to spread the load.

Point the joints

Once the slabs are bedded and the bedding has gone off (24 hours for a wet bed, immediately for a dry bed), fill the joints. Two options:

• Dry mortar pointing — sweep a 4:1 sharp-sand-cement mix into the joints, compact it with a trowel or pointing iron, then mist the surface with water to set it.
• Resin jointing compound — sweep in a pre-bagged permeable resin compound (such as Roma or EasyJoint), wet it down, and it cures hard in 24 hours. More expensive but much faster, and it's permeable so water drains through.

Whichever you use, fill the joints to the full slab depth — shallow joints crack and let weeds in within a season. Brush the surface off before the mortar sets hard, otherwise the haze becomes a permanent stain.

Materials and tools checklist

Materials

• Paving slabs — Indian sandstone, concrete flags, or porcelain
• MOT Type 1 sub-base — allow roughly 150kg per m² at 100mm depth
• Sharp sand — both for bedding and for the mortar pointing
• Cement — for the mortar pointing (or pre-bagged pointing mortar)
• Jointing compound — dry sand-cement or resin-based
• Geotextile membrane (optional) — keeps the sub-base clean if ground is clay

Tools

• Spade and wheelbarrow
• Plate compactor (hire)
• Rubber mallet
• Long spirit level (1.2m or longer) and a 4-foot straight-edge for screeding
• String line and pegs
• Angle grinder with a diamond blade (or block splitter hire)
• Soft brush and pointing trowel

When to call a builder

A 15m² patio is a great DIY project for a long weekend; a 60m² patio that drops 600mm across its length is a different scale of work. Get a builder in if:

• The excavation is over 200mm deep or the ground is awkward
• The area needs significant levelling or retaining
• You want large-format porcelain — these are unforgiving and need a full mortar bed
• Time matters more than budget

We supply the full kit — Type 1, sharp sand, slabs, jointing compound, even the compactor hire — delivered next-day across the South East at trade prices.