Mortar per square metre
| Work | Wet mortar per m² |
|---|---|
| Brick, single skin (half brick), 10 mm joints | 0.032 m³ |
| Brick cavity wall, both skins | 0.055 m³ |
| 100 mm blockwork | 0.014 m³ |
| 140 mm blockwork | 0.017 m³ |
| Render, per 10 mm coat | 0.010 m³ |
| Repointing | 0.006 m³ |
These are the figures the Mortar Mix Calculator uses. Bricks use far more mortar per m² than blocks because there are about 60 bricks to a square metre against 10 blocks.
Choosing the mix
| Designation | Cement:lime:sand | Typical use |
|---|---|---|
| M12 (i) | 1:0.25:3 | Below DPC, engineering brick, retaining walls |
| M6 (ii) | 1:0.5:4.5 | Exposed work, parapets, chimneys |
| M4 (iii) | 1:1:6 | General brick and blockwork above DPC |
| M2 (iv) | 1:2:9 | Internal, low-exposure work |
Use the mix the drawings or the brick manufacturer specify. A mortar much stronger than the bricks makes cracks go through the bricks rather than the joints.
From wet volume to bags and tonnes
- Wet volume = area × mortar per m².
- Dry volume = wet volume × 1.3 (the dry materials bulk down when mixed), plus waste.
- Split the dry volume by the mix parts. A 1:1:6 mix has 8 parts: cement 1/8, lime 1/8, sand 6/8.
- Cement: one 25 kg bag is about 0.0175 m³. Hydrated lime: one bag is about 0.05 m³. Sand: about 1.6 tonnes per m³.
Worked example
25 m² of half-brick facing wall and 15 m² of 100 mm blockwork, in 1:1:6 with 10% waste.
| Step | Working | Result |
|---|---|---|
| Wet volume | 25 × 0.032 + 15 × 0.014 | 1.01 m³ |
| Dry volume, +10% waste | 1.01 × 1.3 × 1.10 | 1.444 m³ |
| One part (of 8) | 1.444 ÷ 8 | 0.181 m³ |
| Cement | 0.181 ÷ 0.0175 | 11 bags (25 kg) |
| Lime | 0.181 ÷ 0.05 | 4 bags |
| Sand | 6 parts = 1.08 m³ × 1.6 | 1.73 tonnes |
Order 11 bags of cement, 4 of lime and a 2 tonne bulk bag of building sand.