How much mortar does a wall take?
The trade figure is one cubic metre of mortar per thousand standard bricks, and about 0.35 m³ per hundred 200-series blocks. Convert either one to wall area and they land in the same place: roughly 44 to 49 litres of mortar per square metre of single-skin wall, whichever unit you are laying.
That figure is generous on purpose, and it is worth knowing why. Add up the joints alone — a 10mm bed and perp around a 230 × 110 × 76 brick — and the geometry says about a third of a cubic metre per thousand. The trade figure is three times that, and the difference is all real: the frog or the cores in the brick swallow mortar, some falls off the trowel, some stiffens in the barrow before you get to it, and some gets raked out and binned. Order to the trade figure, not the geometry.
Because that allowance is already in there, the waste box above is for the rest of it — a messy site, a hot day where batches go off early, a wall you are raking deep for pointing. If you work clean off a board, five per cent is plenty.
A worked example — 2,500 bricks in M3
- Mortar: 2,500 ÷ 1000 = 2.5 m³, plus 10% waste = 2.75 m³
- Dry volume: 2.75 × 1.30 = 3.575 m³
- M3 is 1:1:6, so eight parts. One part = 0.447 m³
- Cement: 0.447 × 1440 = 644kg, which is 33 × 20kg bags
- Lime: 0.447 × 600 = 268kg, which is 14 × 20kg bags
- Sand: six parts = 2.68 m³, or 4.29 tonnes — that is a truck, not a trailer
The three classes, per cubic metre of mortar
| Class | Cement : lime : sand | Where it goes | Cement | Lime | Sand |
|---|---|---|---|---|---|
| M4 | 1 : 0.5 : 4.5 | Below the damp-proof course, retaining, severe exposure | 16 bags | 4 bags | 0.98 m³ |
| M3 | 1 : 1 : 6 | General above-ground external masonry | 12 bags | 5 bags | 0.98 m³ |
| M2 | 1 : 2 : 9 | Internal and sheltered work only | 8 bags | 7 bags | 0.98 m³ |
Notice the sand column does not move. In all three classes sand is three-quarters of the dry volume — what changes is how much cement and lime goes in with it. So sand is the one order you can place before you have settled the class.
Do not just use the strongest mix everywhere
This is the mistake that costs a customer a wall. Mortar is supposed to be weaker than the bricks around it. A wall moves — thermal movement, moisture movement, a bit of settlement — and it has to let that movement go somewhere. If the joint is the weak link, a crack tracks through the mortar, and mortar can be raked out and repointed in an afternoon.
Mix it too rich, and the joint is stronger than the brick. Now the crack goes straight through the units instead, and there is no fixing that short of cutting them out. That is what a 1:3 sand-and-cement mix with no lime in it does to soft bricks.
So take M4 where the exposure calls for it — below the damp-proof course, in the ground, on retaining work, in a severe coastal environment — and use M3 for the general above-ground run of the job. M2 stays inside. Your specification, your engineer or the durability requirements for the site are what decide it; the descriptions above are the general shape of it, not a substitute.
Why lime is in the mix at all
Plenty of people leave it out and think they are saving money. Lime does three jobs cement cannot:
- Workability. Lime makes the mix fat and buttery under the trowel. It sticks to the brick, it stays on the board, and it does not slump off the perp end while you are placing it. Bricklayers lay faster in a limed mix, and speed is money.
- Water retention. A dry brick sucks hard. Without lime the brick pulls the water out of the mortar before the cement has hydrated, and you get a joint with no bond in it — the wall looks fine and the bricks lift off in your hand a week later.
- Self-healing. Free lime in the joint dissolves and re-deposits in fine cracks over time, sealing hairline movement cracks that would otherwise let water in.
One thing to watch when you are buying: lime is light. Hydrated lime is around 600 kg/m³ against cement at 1440, so equal buckets of the two are nothing like equal bags. That is why M3, which is one part cement to one part lime by volume, needs 12 bags of cement and only 5 of lime.
Sand, batching and the wall you actually end up looking at
Use brickies sand — a plasterers or bricklayers sand with the fines still in it. Washed river sand and concrete sand have had the fines taken out, which is exactly what makes them wrong here: the mix comes out harsh, it will not hold water, and it is miserable to lay with.
And be aware that the sand, not the cement, is what colours the wall. A load of yellow sand and a load of grey sand mixed to the same ratio give you two visibly different mortars. Order the whole job from one supplier in one hit, keep it covered, and if you have to top up mid-job, blend the new sand through the old rather than switching over between courses.
- Batch by bucket or a gauge box, never by shovel. A shovel of damp sand and a shovel of cement are different volumes, and the batch-to-batch difference shows up as banding across the wall.
- Cover the sand stockpile. Rain changes how much water the mix wants, which changes the colour and the strength of every batch after it.
- Use a batch within about two hours in normal weather, less in the heat. You can add a splash of water to a mix that has dried out on the board; you cannot bring back one that has started to set.
- Tool the joints at the right moment — thumbprint hard. Too early and you smear it, too late and you burnish the surface and it never weathers evenly.
Mortar sorted. Now sort the paperwork.
Yamate turns the sand, the cement and your hours into a quote the customer accepts on their phone, then an invoice, then a payment — with GST worked out and the chasing done for you.
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How much mortar do I need for 1000 bricks?
About one cubic metre, which is the standard Australian trade figure. In an M3 mix that is roughly 12 bags of cement, 5 bags of lime and just under a cubic metre of brickies sand, before you add a waste allowance.
What is the mortar mix ratio for brickwork in Australia?
The AS 3700 classes are M4 at 1 part cement to 0.5 lime to 4.5 sand, M3 at 1:1:6 and M2 at 1:2:9, measured by volume. M3 is the general-purpose above-ground mix; M4 goes below the damp-proof course and anywhere exposed.
How much sand and cement for 100 blocks?
A hundred 200-series blocks take about 0.35 m³ of mortar. In M3 with a 10% waste allowance that works out to around 5 bags of cement, 2 bags of lime and roughly 0.38 m³ of sand. Enter your own count above.
Do I have to put lime in mortar?
You do not have to, but you should. Lime makes the mix workable, holds water so the brick cannot suck the joint dry before it bonds, and lets fine cracks re-seal themselves. A cement-only mix is harsh to lay and often ends up stronger than the bricks.
Can mortar be too strong?
Yes, and it is a common and expensive mistake. Mortar should be weaker than the units so that movement cracks track through the joint, where they can be raked out and repointed. Too rich a mix sends the crack through the brick instead, and that cannot be repaired.
What sand do I use for mortar?
Brickies sand — a plasterers or bricklayers sand with the fines left in it. Washed or concrete sand has had those fines removed, which makes the mix harsh and poor at holding water. Sand also drives the mortar colour, so buy the whole job in one delivery.
Other calculators you'll want
General information for Australian trades, and an estimate only — not tax, financial or legal advice. It is not engineering, building or design advice either: a calculator works out a quantity from the figures you enter, and anything that needs sign-off still needs your engineer, certifier or building surveyor. Mortar yields and mix proportions are typical published Australian figures and vary with joint thickness, unit type, workmanship and your actual sand. The mix class for a given wall depends on exposure and durability requirements and comes from your specification, your engineer or your certifier — not from this page. Confirm quantities with your supplier before you order.