Sand and cement with no coarse aggregate is mortar, not concrete — the mix you bed patio slabs on, lay bricks with, and render walls in. Enter an area and bed thickness, or a straight volume, and pick your cement to sand ratio.
Which ratio for which job
| Ratio (cement : sand) | Use |
|---|---|
| 1 : 3 | Strong mortar, render scratch coat, exposed repointing |
| 1 : 4 | Patio bedding, general purpose, floor screed |
| 1 : 5 | Standard bricklaying and blockwork mortar |
| 1 : 6 | Softer mix for internal work and older soft bricks |
Sand type matters as much as the ratio. Sharp sand for bedding patios and screeding — the angular grains lock together and resist settlement. Building sand (soft sand) for bricklaying and pointing, because it works smoothly off the trowel. Use the wrong one and you will know within an hour.
Add a proper plasticiser to laying mortar for workability. Not washing-up liquid — it entrains uncontrolled air and weakens the joint, whatever the bloke at the merchant says.
Patio bedding, quickly
A full 30 to 40 mm bed at 1:4 works out at roughly 0.035 m³ of mortar per m², which is about 80 kg of sand and 14 kg of cement for every square metre. A 20 m² patio therefore needs around 1.6 tonnes of sharp sand and 12 bags of cement.
Bed slabs on a full mortar bed, not five dabs. Spot bedding leaves voids under the slab; water gets in, freezes, and the slab rocks or cracks. It is the single most common reason patios fail early.
Frequently asked questions
How much sand and cement for a patio?
About 1.6 tonnes of sharp sand and 12 bags of 25 kg cement for a 20 m² patio on a full 40 mm bed at 1:4. Enter your own area above for exact figures.
What is the ratio for mixing sand and cement?
1:4 for bedding and general mortar, 1:3 for render and stronger work, 1:5 to 1:6 for bricklaying. Exposure and the masonry you are laying decide which end you pick.
How many bags of sand per bag of cement?
At 1:4 by volume, one 25 kg bag of cement takes roughly 100 kg of sand — four 25 kg bags. At 1:5, five bags.
How much does a 25kg bag of sand cover?
About 0.016 m³, enough 1:4 mortar to bed roughly half a square metre at 40 mm. Bulk bags are far better value on anything patio-sized.
Can I use sand and cement instead of concrete?
Only for thin beds, laying and pointing. Without coarse aggregate the mix lacks the compressive strength concrete gets from stone. For anything structural or over 50 mm thick, use the proper concrete ratios.
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