One square metre of single-skin brickwork swallows about 0.02 cubic metres of mortar once the bed joints and perpends are filled. That figure comes from the joint geometry: a ten millimetre bed under every course and a ten millimetre perpend between every brick, across a hundred and two and a half millimetre thickness of wall. Blockwork uses roughly half as much per square metre because there is far less joint per unit of area.
Mortar is bought as its ingredients, not as a volume. A cubic metre of mixed mortar needs about 1.3 cubic metres of dry material, because the cement and the fine sand pack into the voids. Splitting that by the mix ratio and applying bulk densities of 1440 kilograms per cubic metre for cement and 1600 for damp building sand gives the weights you actually order.
A 10 metre wall 2 metres high is 20 square metres, so it needs about 0.40 cubic metres of mortar. At a 1:4 mix that is roughly 150 kilograms of cement and 666 kilograms of sand. Weaker 1:5 and 1:6 mixes are normal for general garden walling and are kinder to soft bricks than a strong mix.
The formula
area- Face area of the wall in m²
rate- Mortar per m² of wall, about 0.02 m³ for single-skin brickwork
n- Parts of sand to one part cement, from the mix ratio
1.3- Dry material volume needed per m³ of mixed mortar
How it works, step by step
- Enter the length and height of the wall face in metres.
- Adjust the mortar rate if you are laying blockwork or a double-skin wall.
- Choose a mix ratio appropriate to the exposure and the brick.
- The gauge shows mortar volume; cement, sand and mixer batches follow.
Worked examples
A 10 m garden wall 2 m high, single skin
20 m² at 0.02 m³/m² is 0.40 m³, or 0.440 m³ with 10% waste. At 1:5 that needs 137 kg of cement — 6 bags of 25 kg — and 0.76 tonnes of building sand.
The same wall in blockwork
Blocks have far less joint per square metre, so the rate drops to about 0.01 m³/m² and the mortar halves to 0.20 m³. The cement at 1:5 falls to about 69 kg, which is why a block wall is quicker and cheaper to build than a brick one of the same size.
How to read your score
Frequently asked questions
Why is 0.02 m³ per square metre the standard figure?
It falls out of the joint geometry. A square metre of half-brick wall contains about 60 bricks, each with a 10 mm bed and a 10 mm perpend across a 102.5 mm wall, and adding those joint volumes together comes to roughly 0.02 cubic metres once you allow for frogs and slight overfilling.
Which mix should I use?
One part cement to five parts sand suits most general brickwork in a sheltered position. Go to 1:4 or 1:3 for exposed work, retaining walls and anything below the damp proof course, and to 1:6 for soft handmade bricks. The mortar must always be weaker than the brick.
Should I add plasticiser or lime?
A plasticiser makes the mix workable without extra water and is normal on site. Lime does the same while allowing slight movement, which is why traditional and conservation work uses a lime mortar. Neither changes the volume of mortar the wall consumes.
How much mortar do I lose in a day?
More than most people expect. Droppings from the trowel, the tail end of a mix that goes off in the barrow and the mortar left on the spot board add up to well over ten per cent for an occasional bricklayer. Mix small and mix often.
Mortar, cement and sand reference
| Wall face area | Mortar | Cement 1:4 | Sand 1:4 | Cement 1:6 | Sand 1:6 |
|---|---|---|---|---|---|
| 2 m² | 0.04 m³ | 1 bags | 0.07 t | 1 bags | 0.07 t |
| 5 m² | 0.10 m³ | 2 bags | 0.17 t | 2 bags | 0.18 t |
| 10 m² | 0.20 m³ | 3 bags | 0.33 t | 3 bags | 0.36 t |
| 20 m² | 0.40 m³ | 6 bags | 0.67 t | 5 bags | 0.71 t |
| 30 m² | 0.60 m³ | 9 bags | 1.00 t | 7 bags | 1.07 t |
| 50 m² | 1.00 m³ | 15 bags | 1.66 t | 11 bags | 1.78 t |
| 80 m² | 1.60 m³ | 24 bags | 2.66 t | 18 bags | 2.85 t |
| 120 m² | 2.40 m³ | 36 bags | 3.99 t | 26 bags | 4.28 t |
Cement counted in 25 kg bags rounded up; sand in tonnes at 1600 kg/m³. Before waste.