How to Lay a Patio: The Steps, Base Depths and Falls That Make It Last

To lay a patio that lasts, you dig out the area, lay and compact a crushed-stone sub-base, set string lines to a fall away from the house, bed each slab on a full bed of mortar, then fill the joints once the bed has set. Most of the work is below the slabs. Patios fail because of what happens underneath, not because of the slabs themselves.

Below is the sequence our team follows on a typical garden patio, with the measurements that matter and the mistakes we're most often asked to put right.

What you need

• A plate compactor (hired), spade, mattock and wheelbarrow

• MOT Type 1 sub-base, sharp sand and cement (or a ready-mixed bedding mortar)

• Pegs, string line, a long spirit level and a rubber mallet

• For porcelain: slurry primer and a diamond blade suited to porcelain

• Jointing compound or grout suited to your slab

• A skip, or a plan for the soil you dig out

Step 1: Plan the size, levels and fall

Mark the patio out with pegs and string. Decide the finished level first: it should sit at least 150mm below the house's damp proof course. Then set a fall away from the house, usually 1:60 to 1:80, so a 4m-deep patio drops roughly 5 to 7cm to its far edge. Knowing where the water will end up is part of this step, and our guide to patio drainage covers the options.

Step 2: Dig out

Excavate to allow for the sub-base, the bedding layer and the slab. For a garden patio that's typically 150-200mm below the finished level, more on soft ground. Remove all topsoil and roots; organic material rots and sinks.

Step 3: Lay and compact the sub-base

Spread MOT Type 1 in layers and compact each one with the plate compactor. Around 100mm compacted is typical for a patio that only takes foot traffic. Shape the sub-base to the same fall as the finished surface, so the mortar bed ends up an even thickness.

Step 4: Set the string lines

Run string lines at finished slab level, with the fall built in. These lines, not the eye, decide the levels. Check them against the spirit level every few metres.

Step 5: Bed the slabs on mortar

Mix a bedding mortar (a common mix is around 4 or 5 parts sharp sand to 1 part cement, workable but not sloppy). Lay a full bed, typically 30-40mm deep, under each slab. Tap the slab down with a rubber mallet to the string line, checking level along and across.

For porcelain, brush a slurry primer onto the back of each slab immediately before it goes down; without it the slab won't bond. Our post on porcelain paving explains why.

Work from a fixed edge, usually the house side, and keep joints consistent with spacers.

Step 6: Cut and fit around edges

Cut slabs with a suitable blade, with water suppression to control silica dust (HSE guidance is clear that dry cutting stone and concrete produces harmful dust). Plan cuts so small slivers end up at the least visible edge.

Step 7: Point the joints

Once the bed has set, usually after a day or two, fill the joints. Brush-in jointing compounds are quick and neat; a traditional wet mortar joint is still common on sandstone. Keep cement off the slab faces, especially on porcelain and light sandstone, where stains are hard to remove.

Step 8: Leave it to cure

Keep off the patio for at least 24 hours and avoid heavy furniture for a few days. Don't lay mortar if frost is forecast.

Can you lay a patio on soil?

Not if you want it to stay flat. Slabs laid straight onto soil sink unevenly as the ground settles and softens in wet weather, and weeds come up through the joints. Even a light-use patio needs the topsoil removed and a compacted sub-base.

Can you lay a patio without cement?

You can lay some slabs on a compacted sand and grit bed, which is how block paving works, but most patio slabs are better on a full mortar bed. Without it, individual slabs rock and shift, and the joints open up. Porcelain in particular needs a mortar bed and primer.

How to lay block paving

Block paving is laid differently. After the sub-base, a layer of sharp sand around 30-50mm is screeded flat (not compacted first), the blocks are laid in pattern on top, edge restraints are fixed in concrete, then the whole area is compacted with a plate compactor fitted with a protective mat, and kiln-dried sand is brushed into the joints. The edges matter most: without solid edge restraints, block paving spreads. For anything a car will drive on, the sub-base goes deeper, which is the kind of job our driveways team handles.

Where DIY patios go wrong

The faults we see most on patios we're asked to redo:

• Too little sub-base, or none, so slabs sink within a year or two

• Spot-bedded slabs that rock and crack

• No fall, so water ponds, or a fall towards the house

• Patio too high against the house wall, bridging the damp course

• Unprimed porcelain lifting off its bed

• Cement stains on the slab faces from careless pointing

When to call a professional

A small, flat patio with good access is a reasonable DIY job if you have the time and hire the right kit. It's worth bringing in a contractor when the garden slopes, when steps or retaining walls are involved, when there's no obvious place for the water to go, or when the patio runs up to new bifold doors where the levels have to be exact.

We lay patios in Kettering and across Northamptonshire, and we'll gladly come and look at the levels, access and drainage and give you an itemised quote. Get in touch if you'd like us to take it on.