Calculating Materials by Weight

Подпись: Simple Worked Example for Brick Walling Project: a one-brick thick wall 12m long and 2.6m high (measured from the top of its foundation), constructed using a mortar mix of 1:2:4 (cement:lime:sand). Number of bricks = 12m x 2.6 x (60 per square metre x 2) = 3744 bricks Add an amount for waste (typically 10 per cent): 3744 + 10 per cent = 4118 bricks Quantity of mortar = 4118 x 1kg/brick = 4118kg in a ratio of 1:2:4 (total of 7 component parts) Cement: (4118kg + 7 parts) x 1 = 588kg + 25kg/bag = 23.53 = 24 bags Lime: (4118kg + 7 parts) x 2 = 1177kg + 25kg/bag = 47.08 = 48 bags Sand: (4118kg + 7 parts) x 4 = 2353kg + 25kg/bag = 94.12 = 95 bags

Calculating quantities of materials for mortar by weight is convenient, as that is how the materials are sold, and it also eliminates the need to take account of volume shrinkage on mixing! When working out quantities of bagged materials, the number must always be rounded up to the next full bag. Rounding down will lead to insufficient quantities. Caution should also be exercised when buying large quantities of sand in bags – it is likely to be much more economic to buy it loose by the tonne.

Project: a 100mm-thick block wall 12m long and 2.6m high (measured from the top of its foundation), constructed using a mortar mix of 1:2:4 (cement:lime:sand).

Number of blocks = 12m ^ 2.6 x 10 per square metre = 312 blocks

Add an amount for waste (typically 10 per cent): 312 + 10 per cent = 343 blocks

Quantity of mortar = 343 x 2.25kg/block = 772kg in a ratio of 1:2:4 (total of 7 component parts)

Cement: (772kg + 7 parts) x 1 = 110kg + 25kg/bag = 4.40 = 5 bags

Lime: (772kg + 7 parts) x 2 = 221kg + 25kg/bag = 8.84 = 9 bags

Sand: (772kg + 7 parts) x 4 = 441kg + 25kg/bag = 17.64 = 18 bags