How to Lay a Patio

Laying a patio is one of the most achievable DIY garden projects, but it is also one of the most frequently done badly. Sunken slabs, cracked pointing, and puddles that sit on the surface for days after rain are almost always caused by the same three mistakes: inadequate sub-base, no drainage fall, or bridging the damp-proof course (DPC) of the house wall. Get the groundworks right and the surface will last 20 years with minimal maintenance.

A competent DIYer working alone on a 20m² patio can expect to spend two to three weekends on the project. Hiring a landscaping contractor for the same area typically takes two to three working days.

Tools and Materials

Tools you will need:

• Spade and/or mini-digger (hire: £100–£180/day)
• Plate compactor (vibrating plate, hire: £50–£80/day)
• Wheelbarrow
• Builder’s line and pegs
• Tape measure and spirit level (1.8m or longer)
• Rubber mallet
• Bolster chisel and club hammer (for cutting slabs)
• Angle grinder with diamond blade (safer for cuts: hire £25–£40/day)
• Pointing trowel and margin trowel
• Mixing board or electric cement mixer (hire: £35–£50/day)
• Safety glasses, gloves, and dust mask (P3 rated when cutting)
• Knee pads

Materials per m² of finished patio:

Waste allowance: add 10% to slab quantities for cuts and breakages. Add 15% for complex patterns or layouts with diagonal cuts.

Step 1: Mark Out and Excavate

Mark the patio area with pegs and builder’s line. Check the line is square using the 3-4-5 method: measure 3 units along one edge, 4 units along the adjacent edge, the diagonal should be exactly 5 units. Scale this up (e.g., 900mm, 1,200mm, 1,500mm) for accuracy over larger areas.

Calculate the total excavation depth:

• 100mm compacted MOT Type 1 sub-base
• 40mm sharp sand mortar bed
• Slab thickness (typically 20–50mm depending on type)
• Total: typically 180–200mm below finished level

The finished surface must be at least 150mm below the DPC of any adjoining house wall. The DPC is usually visible as a thin band of engineering brick, slate, or a physical membrane near the base of the outer leaf, typically 150mm above ground level. Bridging the DPC is a common cause of rising damp and is contrary to Building Regulations (Approved Document C).¹

Excavate to depth and remove all vegetation. Do not simply bury turf, organic material decomposes and causes uneven settlement.

Step 2: Lay and Compact the Sub-Base

The sub-base is the most important part of the build. MOT Type 1 (crushed limestone or recycled concrete aggregate, maximum particle size 40mm) compacts to a dense, stable load-bearing layer. Do not substitute building sand or topsoil, they compress under load and cause slabs to sink.

Pour Type 1 to a loose depth of approximately 130–140mm (it will compact to around 100mm). Rake level, then compact with a plate compactor in overlapping passes. Compact a second time after damping lightly with water, this helps the aggregate bind. The surface should feel solid and not move underfoot.

For areas where heavy vehicles will occasionally mount the patio (a side access, for example), increase the sub-base to 150mm compacted.

Step 3: Set Your Falls and String Lines

A patio must drain. The minimum gradient away from the house is 1:80 (12.5mm drop per metre run). For a 3m deep patio, the outer edge should be 37.5mm lower than the edge adjacent to the house. This gradient is almost invisible to the eye but is sufficient to move water off the surface.

Set your datum (reference level) at the house wall, typically the DPC line minus 150mm. Run builder’s lines across the patio at the finished height, accounting for the drainage fall. These lines guide both the sand bed and final slab heights.

If the patio meets the edge of a lawn or planted border, the outer edge can drain freely. If it is enclosed by a wall, fence, or step, you must either continue the fall to a drainage point or install a linear drain channel at the lowest edge.

Step 4: Mix and Lay the Mortar Bed

The standard mix for a patio mortar bed is 5 parts sharp sand to 1 part Portland cement by volume, this is a semi-dry mix, meaning it holds shape when squeezed but does not slump. It should not be runny. A wetter mix makes levelling easier but reduces strength and increases the risk of slabs sinking during installation.

A full mortar bed is the correct method for patio slabs. Do not use five dabs (one in each corner and one in the centre). Five-dab bedding leaves voids beneath the slab that allow it to flex, crack, and rock underfoot over time. Lay the mortar across the full slab footprint, approximately 40mm deep, raked to the required fall.

For porcelain slabs, a slurry primer (a cement/water/SBR adhesive mix) applied to the back of the slab before laying improves adhesion significantly. Porcelain is non-porous and does not bond as reliably as natural stone to a plain mortar bed.

Step 5: Lay the Slabs

Lower each slab onto the mortar bed and tap firmly with a rubber mallet. Check level and fall with your spirit level against the string lines. Use spacers (5–10mm tile spacers or scraps of ply) to maintain consistent joint width.

Work from a fixed corner outward. Do not kneel on freshly laid slabs, lay boards to spread your weight if you need to reach forward. Allow 24 hours before walking on the surface and 48 hours before loading it. When cutting, score the line first with an angle grinder before cutting through fully; wear eye protection and a P3 dust mask as cutting stone generates silica dust (COSHH Regulations apply).

Step 6: Jointing and Pointing

Allow the mortar bed to cure for a minimum of 48 hours before pointing joints. Pointing too early risks disturbing the slabs.

Dry polymeric jointing compound is the easiest and most durable option for DIYers. Brush the dry compound into the joints with a soft brush, compact it with a pointing tool, remove excess from the slab surface, then activate with a fine mist of water. Polymeric jointing sets hard, is flexible, inhibits weed growth, and does not require the precision of traditional mortar pointing. Cost: £15–£35 per 15kg bag, covering approximately 5–8m².

Traditional mortar pointing (a 3:1 sharp sand:cement mix) is cheaper but harder to execute neatly on large areas. It must be worked into joints firmly without smearing the slab surface. Remove all smears with a damp sponge before the mortar sets, dried mortar stains are very difficult to remove from natural stone.

Costs: DIY vs Hired Labour

Prices exclude skip hire (£200–£350 for a 4-yard skip), which is almost always necessary for excavated material. Groundworks can generate 1.5–2 tonnes of spoil per 10m² at 200mm excavation depth.

Common Mistakes to Avoid

Bridging the DPC. The finished surface must sit at least 150mm below the DPC. Raising ground level against the house wall causes rising damp and can void buildings insurance.

Skimping on the sub-base. A 50mm sub-base over clay will fail within a few years. On clay, increase to 150mm Type 1 and add a weed-suppressing membrane beneath it (not between sub-base and mortar, that breaks the bond).

No drainage fall. A flat patio or one falling towards the house is a damp risk. Check your fall at every stage with a long spirit level.

Five-dab bedding. Voids beneath slabs cause rocking, flexing, and cracking under load. A full bed is always correct and is the standard under BS 7533-102:2025, which replaced the withdrawn BS 7533-4.²

Pointing too early. Allow the mortar bed at least 48 hours before pointing, disturbed joints crack. Surface drainage to foul sewer is also prohibited; keep surface water and foul drainage separate (Building Regulations Approved Document H).³

Planning Permission

Most ground-level patios do not need planning permission within a dwelling’s curtilage. However, laying a hard surface in the front garden has its own permitted development right, Class F of Schedule 2 Part 1 of the GPDO, and it is conditional: an area of more than 5 m² between the house and a highway is permitted only if the surface is porous, or if the run-off is directed to a porous or permeable area within the curtilage. Above 5 m² and impermeable with nowhere for the water to go, it needs planning permission. Use a permeable jointing compound and ensure runoff drains to soft landscaping to stay within permitted development rights. Conservation areas and listed buildings have stricter rules, check with your local planning authority before starting.⁴

The rules in this note are those that apply in England. Scotland, Wales and Northern Ireland have their own building standards and permitted development rights.