Guide
Mortar mix ratios explained
Mortar mixes are written as cement to sand by volume: 1:4 is a strong general mix, 1:5 suits most above-ground brick and blockwork, and 1:6 is a softer mix for less exposed work, often with a plasticiser or lime added.
Written by the SK Trade team. Last reviewed 1 November 2026.
Common mixes
| Mix (cement : sand) | Typical use |
|---|---|
| 1:3 | Strong mix for below-ground or very exposed work, as specified |
| 1:4 | General mix, below DPC, copings and exposed walls |
| 1:5 | Most above-ground brick and blockwork |
| 1:6 | Internal and sheltered work, often with plasticiser |
Your design or building control may specify a mortar designation; follow it where it exists.
Materials per cubic metre of mortar
Dry materials bulk down when mixed, so allow about a third more dry volume than the wet mortar you need. On that basis, one cubic metre of 1:4 mortar needs roughly 380 kg of cement (about 15 bags of 25 kg) and 1.7 tonnes of building sand. A 1:5 mix needs about 320 kg of cement and 1.8 tonnes of sand.
Plasticiser and lime
Plasticiser makes mortar easier to work and improves frost resistance at weaker mixes. Lime does a similar job and is preferred for older buildings that need to breathe. Do not use washing-up liquid as a plasticiser.
Working in cold weather
Do not lay mortar when the temperature is near freezing or falling towards it, and protect fresh work from frost and heavy rain overnight.
Safety
Wet cement is alkaline and can burn skin. Wear waterproof gloves and eye protection, and wash splashes off quickly with clean water.
Related products
Related questions
How many bags of cement in a cubic metre of concrete?
For a 1:5 cement to all-in ballast mix, roughly 15 bags of 25 kg cement per cubic metre. Our concrete calculator gives the full list.
What is the difference between building sand and sharp sand?
Building (soft) sand is fine and makes smooth mortar for laying bricks. Sharp sand is coarser, drains better and is used in concrete, screeds and paving beds.
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