Laying a patio on a sand and cement bed looks straightforward until the first slab rocks under your heel. Get the sub-base right, keep your falls honest and mix the mortar to the correct consistency, and a DIY patio will comfortably outlast the fence around it. Cut corners on any of those three and you will be lifting slabs again next spring.

What follows is the full sequence for a typical UK garden: digging out, compacting, setting levels, bedding the slabs, cutting, pointing and keeping rainwater away from the house. Work at a steady pace, one section at a time, and it is a job most confident DIYers can handle over a long weekend or two.

What You Will Need

• Materials: MOT Type 1 sub-base, sharp sand, building sand, general-purpose cement, SBR additive or plasticiser, 10–12mm spacers, and a weed membrane if you are laying over soil.
• Tools: wheelbarrow, shovel, rake, plate compactor, string line and pegs, 1.2m spirit level, rubber mallet, pointing trowel, bucket, angle grinder with a diamond blade, and a straight edge for checking.
• Safety kit: safety glasses, ear defenders, gloves, a dust mask for cutting, and knee pads.

Order around ten per cent more slabs than your measured area. Breakages, cuts and a change of mind at the edges all eat into the total, and matching a batch months later is rarely straightforward.

Get the Levels and Falls Right First

Water is the enemy of every patio, so decide where it is going before you dig anything. Aim for a fall of roughly 1:60 to 1:80 — that is about 15–25mm of drop over each metre — running away from the house and any other building. A subtle slope is unnoticeable underfoot but keeps puddles from forming.

Set up a string line along the wall and another at the far edge, then check the difference with your level. The finished patio surface should sit at least 150mm below the damp proof course, which is roughly two brick courses. Anything higher risks bridging the DPC and pushing damp into the wall.

Also think about where the water ends up. Running it straight at a neighbour's boundary or into your own footings is asking for trouble; a soakaway, border or rain garden handles it far better. If your plans change how the garden drains, or the patio sits tight to a boundary, it is worth checking your local authority's guidance before you start.

Dig Out and Build the Sub-Base

Allow for the full build-up: 100mm of compacted Type 1, then 30–40mm of bedding mortar, then the slab itself. For 40mm slabs that means excavating roughly 175–200mm, plus a little more on soft ground.

Spread the Type 1 in two 50mm layers rather than one thick one, and compact each layer thoroughly with the plate compactor, overlapping your passes. Dampen it lightly if it is dusty, but do not flood it. Finish 30–40mm below your intended slab level so the bedding has room. On heavy clay, a woven weed membrane under the sub-base stops soil migrating upward and helps the base stay put.

Mixing the Bedding Mortar

Use a 5:1 mix of sharp sand to cement for a semi-dry bed, or 4:1 if you prefer a slightly wetter mix that is easier to tap slabs down into. Sharp sand is the right choice here — its gritty texture grips the slab, whereas soft building sand is saved for pointing.

Judge the consistency with a simple test: squeeze a handful in your fist. It should hold its shape like damp sand for a sandcastle, without water running out. Too wet and the slab will sink and slump; too dry and it will not bond.

Mixing SBR into the water, following the dilution on the bottle, gives a noticeably stronger bond and is worth the small extra cost on a patio that will take foot traffic and the occasional frost. Combine the sand and cement dry first, then add water gradually. Mix only what you can lay in about an hour — less on a hot day, because mortar that has started to go off should be binned, not revived with a splash of water.

Laying the Slabs

Start at a fixed edge — a wall, a manhole cover or a string line — and work away from it. Spread the mortar to a consistent 30–40mm and never dot-and-dab with five blobs; a full bed supports the slab evenly and stops it cracking.

1. Lay the slab onto the bed and press it down firmly with the rubber mallet.
2. Check the fall and level with your spirit level, working along the run as well as across.
3. If it needs adjusting, lift the slab, add or scrape away mortar, and try again — it is quick once you have the rhythm.
4. Insert 10–12mm spacers at the corners to keep joints even.
5. Kneel or walk on the laid slabs, never on the soft bedding, and recheck levels every few slabs so errors do not creep in.

Cut slabs with an angle grinder and diamond blade, outdoors, with the slab well supported and your dust mask on. Cut from the face side to reduce chipping; if you are working with porcelain, a wet cutter gives a far cleaner edge. Give the mortar at least 24 hours before walking on the new surface.

Pointing the Joints

Leave pointing for at least a day, ideally two, so the bedding has firmed up. Mix 4:1 building sand to cement with a plasticiser or SBR, keeping it stiff enough to hold in the joint without slumping.

Work the mortar in with a pointing trowel or a mortar gun, pack it down properly, and strike the joint smooth with a pointing iron or the edge of your trowel. Clean any smears off the slab face immediately — once cement dries on sandstone or porcelain, it is a job and a half to remove. Keep foot traffic off the joints for 24–48 hours, and mist them with water on a hot day to help the mortar cure rather than dry out too fast.

Drainage, Edges and Aftercare

Check the fall one last time with a bucket of water. If the patio runs towards the house and there is no way to reverse it, fit a linear channel drain at the threshold and connect it to a suitable outlet. Never let the finished level sit over an air brick.

Edge restraints matter more than most people expect. Slabs at the perimeter try to spread outward, so haunch them with a stiff mortar mix or bed them against setts, kerbs or a low retaining edge. Once everything has cured, sweep regularly, treat algae with a suitable patio cleaner, and reseal natural stone if the manufacturer recommends it. Most importantly, do not lay in frosty weather — mortar needs to stay above roughly 5°C to set properly.

When to Call in Help

If your garden slopes steeply, needs a retaining wall, sits over deep excavation or requires drainage connected to the mains, bring in a professional. Those jobs carry real risk of movement and water damage that a sand and cement bed alone will not solve. For a flat, straightforward area, though, the method above is well within reach — take your time on the levels, mix to the right consistency, and the finished patio will sit flat and firm for years.

Photo: Jupilu / Pixabay