Free Mortar Mix calculator with clear step-by-step results.
Mortar volume per square metre depends on the wall construction - a one-brick-thick wall needs more than twice the mortar of a single skin because of the collar joints. Wet volume is grossed up by a dry factor before being split by the mix ratio, and sand is converted to tonnes at typical bulk density.
Mortar volume
Volume = wall area x mortar per m2 for the construction x (1 + waste)
Cement volume
Cement = wet volume x 1.33 / (1 + sand parts)
Mortar specification for structural masonry, exposed situations and below-ground work is governed by design standards. Over-strong mortar can damage soft masonry - take advice on historic buildings.
Mortar is mixed in gauges, dropped from the trowel, and stiffens before it can all be used. Fifteen percent is realistic and twenty is not unusual on a windy day.
Lime improves workability and lets the mortar accommodate movement without cracking, which matters on soft historic brick. Modern plasticisers entrain air for similar workability but less flexibility.