Brick Mortar Calculator

Brick Mortar Calculator: The Complete Guide

Getting your mortar quantities right before you start bricklaying avoids the frustration of running short of cement halfway through a job, prevents overspending on materials you will not use, and ensures your mortar mix is consistent from the first course to the last. This guide explains how mortar quantities are calculated for different brick types in South Africa, how mix ratios affect cement and sand quantities, what the yield factor means, and which mix to use for your specific application.

What is brick mortar and why does the quantity matter?

Brick mortar is the cement and sand mixture that fills the joints between bricks, binding them together and distributing loads evenly across the wall. For every brick you lay, a bed of mortar sits below it and perpend joints fill the ends. The volume of mortar per brick is surprisingly consistent once the brick size and joint width are fixed, which is why the Clay Brick Association of Southern Africa publishes standard mortar consumption figures per 1000 bricks. Underestimating mortar leads to a second, usually more expensive, purchase. Overestimating results in wasted mixed material that cannot be stored or reused once it begins to set.

How much mortar do you need per brick?

For a standard South African brick (222 x 106 x 73mm) laid with a 10mm mortar joint, the wet mortar consumption is approximately 0.00037 cubic metres per brick, or roughly 0.37 cubic metres per 1000 bricks. This figure accounts for the bed joint below each brick and the perpend joints at each end, based on the brick’s face area and the standard joint size. Maxi bricks (290 x 140 x 90mm) are larger, so each brick covers more wall area but also displaces more mortar per unit. Hollow concrete blocks use proportionally more mortar due to their larger face dimensions. This calculator adjusts the mortar volume per unit automatically based on your chosen brick type.

Mortar mix ratios for South African brickwork

South African brickwork mortar is specified by a cement-to-sand ratio by volume. The most common ratios and their applications are:

• 1:6 cement to building sand: The standard mix for most residential brickwork in South Africa, producing a Class II mortar as referenced by the Clay Brick Association. Suitable for freestanding walls, boundary walls, garden walls, internal walls and general loadbearing masonry.
• 1:4 cement to building sand: A stronger Class I or Class II mortar used for exposed brickwork, parapet walls, below damp-proof-course work, retaining walls and brickwork subject to heavy loading or wind exposure.
• 1:3 cement to building sand: A very strong, dense mix used for foundations, wet areas, piers, columns and any application requiring maximum mortar strength. Not typically used for general walling as it can be brittle and prone to cracking if the substrate moves.
• 1:5 cement to building sand: A general-purpose mix between the standard and strong options, sometimes specified for internal plastered brickwork or where a slightly stronger than standard mortar is preferred without the full cost of a 1:4 mix.

What is the yield factor and why does it matter for mortar?

When dry cement and building sand are mixed with water to form mortar, the resulting wet volume is approximately 30–35% less than the combined dry volume of the ingredients. This is because cement particles fill the voids between sand grains as they hydrate, compacting the overall mix. Without applying a yield factor, you will calculate too little dry material to produce the mortar volume you actually need. This calculator applies a standard 33% yield factor, dividing the required wet mortar volume by 0.67, to give you accurate dry cement and sand quantities.

Cement and sand quantities per 1000 standard bricks at different mix ratios

• 1:6 mix: Approximately 3 bags of 50kg cement and 0.6 m³ of building sand per 1000 standard bricks, based on Clay Brick Association guidance.
• 1:4 mix: Approximately 4–5 bags of 50kg cement and 0.5–0.6 m³ of building sand per 1000 standard bricks.
• 1:3 mix: Approximately 6 bags of 50kg cement and 0.5 m³ of building sand per 1000 standard bricks.

Standard brick types and mortar consumption in South Africa

• Standard / Stock Brick (222 x 106 x 73mm): The most widely used brick for South African house walls and boundary walls. Approximately 50 bricks per square metre for a single-skin wall and 100 per square metre for a double-skin wall, with around 0.37 m³ of wet mortar per 1000 bricks.
• Maxi Brick (290 x 140 x 90mm): A larger brick requiring fewer units per square metre (approximately 28 single skin, 56 double skin), but using more mortar per brick due to its larger face and bed areas.
• Hollow Concrete Block (390 x 190 x 190mm): Larger units used for boundary walls, retaining walls and sections below damp-proof course. Approximately 12.5 blocks per square metre for a single-skin wall, with proportionally more mortar per unit than standard bricks.

Single skin vs double skin walls and mortar quantity

A single-skin, or half-brick, wall is one brick thick (approximately 110mm for standard bricks) and is the standard for internal walls, garden walls and many boundary walls. A double-skin, or full-brick, wall is two layers thick (approximately 220mm) and is used for external loadbearing walls carrying a roof or upper floor. Double-skin walls use roughly twice as many bricks and therefore require approximately twice as much mortar per square metre of wall face area. This calculator applies the correct bricks-per-square-metre figure for each wall type when you choose to calculate by wall area.

Why wastage allowance matters for mortar

Mortar is always lost to some degree through mixing spillage, material left on the board and tools, slight over-filling of joints, and variation in joint thickness across a wall. Adding 10% to your calculated cement and sand quantities is standard practice in South African construction. It is much cheaper and less disruptive to have a small surplus than to have to mix a second partial batch midway through a wall, which can result in a slightly different mortar colour or consistency in the finished joints.

Tips for consistent, waste-free mortar mixing

• Use a gauge box for batching. Measuring by bucket or wheelbarrow introduces significant variation between batches. A simple timber gauge box ensures a consistent ratio from mix to mix and produces a more uniform finish.
• Mix only what you can use in 30–45 minutes. Mortar begins to set after roughly an hour of mixing, especially in hot or dry conditions. Mixing too large a batch wastes material and reduces bond strength if laid after stiffening begins.
• Do not re-temper stiffening mortar. Adding water to mortar that has begun to stiffen reduces its final compressive strength significantly. Discard and mix a fresh batch.
• Use building sand, not plaster sand or river sand. Building sand (soft pit sand) produces the correct workability and bond strength for brickwork mortar. Plaster sand is too fine and river sand is often too coarse, both affecting mortar performance and joint appearance.
• Check mortar colour consistency. Variations in sand source or water content between batches can cause visible colour differences in exposed face brick joints. Stick to one sand source and measure water consistently.
• Confirm structural requirements with an engineer. This calculator provides material estimates for residential brickwork only. Retaining walls, piers, columns and any loadbearing structure should have the mortar mix specification confirmed by a qualified structural engineer.

Methodology

Mortar consumption figures used in this calculator are based on Clay Brick Association of Southern Africa guidance and standard South African construction industry practice. Standard brick mortar volume is derived from approximately 0.00037 m³ of wet mortar per brick at a 10mm joint. Maxi brick mortar volume is adjusted proportionally for the larger bed area (approximately 0.00083 m³ per brick). Hollow concrete block mortar volume is calculated at approximately 0.0012 m³ per block at a 10mm joint. A 33% yield factor is applied to convert wet mortar volume to the dry material quantities needed. One 50kg bag of cement equals approximately 0.033 m³ of loose dry cement. Sand quantities are rounded up to the nearest 0.1 m³. Cement bags are rounded up to the nearest whole bag. A 10% wastage allowance is added when selected. Actual quantities vary based on joint thickness, workmanship and site conditions.

Assumptions used in this calculator

• All mortar volumes assume a standard 10mm bed and perpend joint.
• Standard brick: 0.00037 m³ wet mortar per brick. Maxi brick: 0.00083 m³ per brick. Hollow block: 0.0012 m³ per block.
• A 33% yield factor is applied (wet volume ÷ 0.67) to give correct dry material quantities.
• One 50kg bag of cement = 0.033 m³ loose dry volume.
• Wastage, when applied, adds 10% to all quantities.
• Preset wall areas use standard coverage rates: 50 standard bricks/m², 28 maxi bricks/m², 12.5 hollow blocks/m² for single skin.
• This tool does not calculate bricks, reinforcing steel, foundations, plaster, DPC or material costs.