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Project guide

How much sand and cement do I need for bricks, blocks or slabs?

Work out the volume of mortar first, then split it into cement and sand by the mix. Here are the standard UK rates for brickwork, blockwork and laying paving slabs.

Updated Based on manufacturer guidance, sources below

The short answer

A half-brick wall uses about 0.03 m³ of mortar per m² (60 bricks), 100mm blockwork about 0.012 m³ per m² (10 blocks), and a 40mm slab bed 0.04 m³ per m². A 1:4 mix takes about 14 x 25kg bags of cement and 1.5 tonnes of sand per m³. A 5m garden wall, 0.9m high, needs about 284 bricks, 3 bags of cement and 1 bulk bag of building sand.

The formula

  • Mortar (m³) = area x rate x 1.1; rate = 0.03 (bricks), 0.012 (100mm blocks), 0.04 (40mm slab bed)
  • Cement (25kg bags) = mortar m³ x 19 (1:3), 14 (1:4), 12 (1:5) or 10 (1:6)
  • Sand (tonnes) = mortar m³ x 1.5
  • Bricks = area x 60, plus 5%; blocks = area x 10, plus 5%

Worked example

A half-brick garden wall 5m long and 0.9m high (4.5 m²), 1:4 mix:

  • Bricks: 4.5 x 60 = 270, plus 5% = 284
  • Mortar: 4.5 x 0.03 x 1.1 = 0.15 m³
  • Cement: 0.15 x 14 = 2.1, so 3 bags
  • Building sand: 0.15 x 1.5 = 0.22 tonnes, so 1 bulk bag (or about 9 x 25kg bags)

A 4 x 3m patio on a 40mm bed of 1:4 cement to sharp sand needs about 0.53 m³ of mortar: 8 bags of cement and about 0.8 tonnes of sharp sand.

Work it out for your job

Change the measurements and the quantities update straight away.

Wall length x height, or patio length x width.
Bricks
284 (60 per m² + 5%)
Mortar
0.15 m³ (including 10%)
Cement
3 x 25kg bags (1:4)
Building sand
0.22 tonnes, about 1 bulk bag

Your list

  • 3Cement 25kg
  • 1Building sand, bulk bags
  • 1Mortar plasticiser 1L
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Materials checklist

  • Cement25kg bags of general-purpose cement.
  • Building (soft) sandFor bricklaying and blockwork mortar.
  • Sharp sandFor a slab bedding mortar, as Marshalls specifies.
  • Mortar plasticiserMakes bricklaying mortar easier to work. Follow the dose on the bottle.
  • Bricks or blocks60 bricks or 10 blocks per m², plus 5%.
  • MOT Type 1 sub-base (patios)About 100mm, compacted, under the slab bed.
  • Paving primer (patios)Marshalls recommends priming slab backs before laying.

You'll also need

  • Mixer or a large mixing tub, shovel and buckets
  • Brick trowel, pointing trowel and jointer
  • Spirit level, string line and line pins
  • Rubber mallet for slabs
  • Gloves and goggles: wet cement burns skin

Step by step

  1. Measure the areaWall length x height for brick and blockwork, or length x width for a patio.
  2. Work out the mortarMultiply by 0.03 (bricks), 0.012 (blocks) or 0.04 (slab bed), and add 10%.
  3. Choose the mix1:4 for most walls, 1:3 below the damp-proof course or in exposed spots, 1:3 to 1:4 sharp sand mortar for slabs.
  4. Split into cement and sandAbout 14 bags of cement and 1.5 tonnes of sand per m³ for a 1:4 mix.
  5. Mix in batchesMix only what you can use in about an hour, measuring by the bucket so every batch matches.

Tips from the manufacturers

  • Measure cement and sand by volume with the same bucket, not by bag: "1:4" means 1 bucket of cement to 4 of sand.
  • Marshalls lays paving slabs on a full, wet bed of 1 part cement to 3 or 4 parts sharp sand, 30 to 40mm thick, which tamps down to about 25mm. Every slab should be fully supported.
  • Marshalls says never to brush dry or semi-dry sand and cement into slab joints: it stains and does not make a proper joint. Point with a wet mortar or a jointing compound.
  • Use building (soft) sand for bricklaying. Sharp sand makes a harsh mortar that is hard to work.

Mistakes to avoid

  • Laying slabs on five dabs of mortar, which leaves voids that rock and crack.
  • Using a mix much stronger than the bricks, which can crack soft older bricks.
  • Mixing more mortar than you can use before it starts to set.
  • Building a garden wall over 2m high (or 1m next to a road) without checking planning rules, or without a proper footing.

Frequently asked questions

How much mortar per 1000 bricks?

About 0.5 to 0.65 m³ for standard bricks with 10mm joints, which is roughly 7 to 10 bags of cement at 1:4.

How many bricks per m²?

About 60 standard UK bricks (215 x 102.5 x 65mm) per m² of half-brick wall with 10mm joints.

What mix for laying paving slabs?

Marshalls specifies a full, wet bed of 1 part cement to 3 or 4 parts sharp sand, 30 to 40mm thick.

How much sand and cement for a patio?

For a 40mm bed, allow 0.04 m³ of mortar per m² plus 10%. A 12 m² patio needs about 0.53 m³: 8 bags of cement and about 0.8 tonnes of sharp sand at 1:4.

How much cement goes with a bulk bag of sand?

An 800kg bulk bag is roughly 0.53 m³ of mortar's worth of sand. At 1:4 that pairs with about 8 bags of cement.

Sources

Quantities are estimates for typical jobs, using the coverage figures above. Products vary, so check the data sheet for the product you buy, and talk to a professional for structural, electrical or gas work. SmartBuild is independent and not affiliated with any of the manufacturers listed.

How much concrete do I need for a shed base?Make the base a little bigger than the shed, work out the volume, and convert it to bags of cement and ballast for a 1:5 mix. How many fence panels and posts do I need?Divide the length of the run by the panel width and round up. You need one more post than panels, plus one for each corner or gate. How many tiles do I need, and how much adhesive and grout?Work out the area, divide by the size of one tile and add 10% for cuts. Adhesive and grout depend on where you are tiling and the joint size.

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