How many bags of mortar per brick?
Cement Australia rates one 20kg bag of Trade Mortar at about 20 house bricks or 10 masonry blocks with a 10mm joint. Cement Australia's mortar calculator assumes a 230x110x76mm brick and a 390x190x190mm block.
Trade Mortar is pre-blended M4 mortar to AS 3700, so it only needs water: about 3.5 litres a bag, added gradually.
Mixing your own mortar
If you batch your own from cement, lime and sand, these are the usual ratios by volume:
| Mortar | Cement : lime : sand | Use |
|---|---|---|
| Mortar M3 (AS 3700), similar to US Type N | 1 : 1 : 6 | General brickwork |
| Mortar M4 (AS 3700), similar to US Type S | 1 : 0.5 : 4.5 | More durable: exposed, coastal and below-damp-course work |
Working time
Mix only what you can use within an hour. Adding water to mortar that has started to stiffen weakens it.
Questions
About 20 house bricks per 20kg bag of Trade Mortar, or 10 masonry blocks, with a 10mm joint (Cement Australia).
About 3.5 litres per 20kg bag, added slowly. Use the least water that gives a workable mix.
Both are durability classes in AS 3700. M4 is the more durable class, for exposed, coastal and below-damp-course work, and is what Trade Mortar is made to; M3 suits general brickwork.
Use it within an hour. Re-tempering a stiffened batch with more water weakens it.
Goes with this job
Disclaimer
This calculator gives estimates from the sizes you enter, using manufacturers' published figures and standard geometry. It is not engineering or design advice. Footing, slab and beam sizes must come from your plans or engineer. Allow for site conditions, spillage and uneven ground. Check quantities with your supplier before ordering. Allmat accepts no responsibility for decisions made using these estimates.
Sources
- Cement Australia: Trade Mortar
- Cement Australia: volume batching mix table
- Allmat arithmetic (this calculator)
Last checked 5 October 2026.
Cite this page
Allmat, "Mortar calculator", https://allmat.com.au/concrete-calculator/mortar, checked 5 October 2026.