Mortar and estimation of mortar requirement

Mortar

Mortar is a paste of binding material (cement or lime), fine aggregate (sand) and water; it is used to join bricks or stones, fill joints and plaster surfaces. Common types are cement mortar (1:3 to 1:6), lime mortar, cement-lime (gauged) mortar and mud mortar.

Estimation of mortar requirement

The mortar needed depends on the volume of masonry and the volume of units in it.

1. Find the volume of brickwork $V$ (m³).
2. Find the size of a brick with mortar, e.g. $(240+10)\times(115+10)\times(57+10)$ mm, and the number of bricks $N = V/\text{volume of one brick with mortar}$.
3. Volume of bricks without mortar $= N \times 0.24 \times 0.115 \times 0.057$.
4. Wet volume of mortar $= V -$ volume of bricks.
5. Dry volume $=$ wet volume $\times$ 1.27 (to account for voids in sand, shrinkage and wastage).
6. Divide by the mix ratio $1:n$: cement $= \dfrac{\text{dry volume}}{1+n}$, sand $= \dfrac{n}{1+n}\times\text{dry volume}$.
7. Convert cement to bags: 1 bag (50 kg) $= 0.0347$ m³.

Worked example (10 m³ brickwork, 1:6)

• Bricks $= 10/(0.25\times0.125\times0.067) \approx 4777$.
• Brick volume $= 4777 \times 0.0015732 = 7.515$ m³.
• Wet mortar $= 10 - 7.515 = 2.485$ m³; dry $= 2.485 \times 1.27 = 3.156$ m³.
• Cement $= 3.156/7 = 0.451$ m³ ($\approx$ 13 bags); sand $= 3.156 \times 6/7 = 2.705$ m³.

For plaster: mortar volume $=$ area $\times$ thickness $\times$ 1.27 (dry).