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Sharp (grit) sand, product photo from the Insulation Warehouse Direct range

Sand and Cement for Paving: How Much Bedding Do You Need per m²?

By , Managing Director · Updated

The bedding layer is what stops paving slabs rocking, and it is also the layer people most often under or over-order. The amount you need depends on how thick the bed is and what it is made from, so rather than quoting a single number, this guide shows the working. You can then adjust it for your own paving and your own layer depth.

Check how your paving should be laid

Different paving products have different recommended bedding methods. Natural stone, porcelain and concrete slabs can each call for a specific mortar mix, a full mortar bed, spot bedding or a priming slurry. Always follow the manufacturer's laying instructions, which take priority over any general guide. This article gives typical quantities, not a specification.

Two layers commonly sit between the sub-base and the slab:

  • A sharp sand layer, commonly roughly 30 to 50mm deep, often used under block paving and some slabs.
  • A sand and cement mortar bed, often around 30 to 50mm deep for a full bed under slabs. A typical mix is sharp sand and cement in a ratio of roughly 4 to 6 parts sand to 1 part cement by volume, as discussed in our guide to sand and cement mix ratios.

Sand per m² for a sand bedding layer

For a 40mm layer:

  • Volume per m²: 1 × 0.04 = 0.04m³
  • Add 10% for levelling and waste: 0.044m³
  • Loose sharp sand weighs very roughly 1.6 tonnes per m³: 0.044 × 1.6 = about 70kg per m²

So allow about 70kg of sharp sand for every square metre at 40mm deep. At 30mm it is about 53kg and at 50mm about 88kg, since it scales directly with depth.

Sand and cement per m² for a mortar bed

This is our own working, not a manufacturer's figure, so treat it as a starting point. For a 40mm mortar bed mixed at 1 part cement to 4 parts sharp sand:

  • Wet mortar per m²: 0.04m³
  • The dry materials are bulkier than the finished mortar. Allowing roughly 30% more gives about 0.052m³ of dry mix
  • At 1 : 4, that is one fifth cement (about 0.010m³, roughly 15kg) and four fifths sand (about 0.042m³, roughly 65 to 70kg)

That is roughly 15kg of cement and 65 to 70kg of sharp sand per m², or around half a 25kg bag of cement per square metre. A weaker mix uses less cement per m² and a stronger one uses more.

Worked example: a 12m² patio

Take the 4m × 3m patio from our guide to how much MOT Type 1 you need for a patio.

Option 1: a sand bedding layer at 40mm

Option 2: a mortar bed at 40mm, 1 : 4

  • Cement: 12 × 15kg = about 180kg, which is 7 to 8 bags of 25kg Blue Circle General Purpose cement
  • Sharp sand: 12 × 67kg = about 0.8 tonnes, so 1 bulk bag, or 2 to be safe

Buy a little extra. A bed that is a few millimetres deeper than planned over 12m² adds up quickly, and running short in the middle of laying is a problem, because mortar will not wait.

Tips for a flat, stable finish

  • Screed the bed level using rails or a straight edge, then lay each slab and tap it down.
  • Keep the sub-base firm and flat. A good bedding layer cannot make up for a poor base. See our guide to sub-bases for driveways or the patio guide above.
  • Allow for a fall of the patio away from buildings so water drains off.
  • Keep the sand dry and covered. A bulk bag left in the rain gets heavier, and wet sand is harder to level.

Combining with other aggregates

Aggregates and cement have a £250 ex VAT minimum order. A typical patio job needs sub-base, bedding sand and cement together, so you can combine them on one order, and bulk bags of sub-base and sand will usually clear the minimum.

Frequently asked questions

How thick should the bedding layer be?

It depends on the paving and the method, but a layer of around 30 to 50mm is typical. Check the manufacturer's laying instructions for your slabs.

Should I use sharp sand or building sand for bedding?

Sharp sand is the usual choice. See our sharp vs building sand guide.

Do I need cement in the bedding layer?

Often yes for slabs, where a mortar bed is common, and sometimes no for a plain sand layer under blocks. It depends on the paving, so follow the manufacturer's instructions.

How much extra should I order?

A 10% allowance for levelling and waste is a sensible start. Order more if the base is uneven or you are unsure.

How many bags of cement do I need?

On the working above, roughly half a 25kg bag per m² for a 40mm bed at 1 : 4, so about 7 to 8 bags for 12m². Check the amounts against your paving manufacturer's guidance.

Ordering and delivery

You can browse the full range in our cement and aggregates collection. Bulk bags are sold at approximately 800kg each (the packed weight can be up to 850kg depending on moisture), and most sands and gravels are also available in 20 to 25kg trade packs for small jobs. Prices on our website are shown excluding VAT, and VAT is added at checkout.

We deliver to addresses in mainland England only; we do not currently deliver to Wales, Scotland, Northern Ireland or the islands. Timber, aggregates and cement have a minimum order of £250 ex VAT, and delivery is £25 ex VAT on orders under £500 ex VAT and free over £500 ex VAT. Bulk bags are delivered by Moffett lorry (truck-mounted forklift) and offloaded at your site, so someone must be there to receive them and you will need a firm, level area with suitable access. We do not offer next-day delivery. Our shipping policy has the full details, or call us on 03330 908479 or email sales@insulationwarehousedirect.co.uk if you would like a hand working out your order.

The quantities in this guide are estimates. Ground levels, how well the material is compacted and how wet it is all change what you need, and densities vary between quarries, so check the amount with your installer or the manufacturer's guidance before you order. Prices and pack sizes are correct at the time of writing.

Working out quantities? See our MOT Type 1 sub-base guide: how much do I need? or go straight to our aggregates calculator.

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