Concrete mix ratios
By Tom Drake | 29th November 2024 | 4 min read
Whether you’re laying a concrete slab for a shed or creating a path, you need to get the ratio of materials in your concrete right. In this guide, we outline the concrete ratios you need to know to get the correct mix for your job.
What is concrete made of?
Concrete is made of cement, water, sand and aggregates such as gravel or crushed stone.
If you don't want to measure out sand and aggregates separately, you can use ballast. Ballast is a mixture of sand and gravel that can be combined with cement to make concrete.
Concrete mix ratios
A popular mix ratio for concrete is 1:2:3, which consists of 1 part cement, 2 parts sand, and 3 parts aggregates. The 1:2:3 mix ratio offers good strength and is easy to work with. This makes it ideal for common DIY jobs such as shed bases.
This ratio won’t be suitable for all projects, so below, we outline 3 common concrete mix ratios and their uses.
Standard strength concrete mix ratio
- 1 part cement
- 2.5 parts sharp sand
- 3.5 parts aggregates
Using ballast:
- 1 part cement
- 5 parts ballast
The 1:2.5:3.5 concrete mix ratio offers adequate strength for light wall foundations and concreting in fence posts.
Medium strength concrete mix ratio
- 1 part cement
- 2 parts sand
- 3 parts aggregates
Using ballast:
- 1 part cement
- 4 parts ballast
The 1:2:3 concrete mix ratio is ideal for concrete bases such as shed or garage bases. It offers good strength whilst still being easy to work with.
Strong concrete mix ratio
- 1 part cement
- 1.5 parts sharp sand
- 2.5 parts aggregates
Using ballast:
- 1 part cement
- 3.5 parts ballast
The 1:1.5:2.5 concrete mix ratio is a stronger mix that is ideal for steps, paving and driveways that will be exposed to the weather.
Water
It’s important to remember that the amount of water you use when mixing your concrete will also affect its strength. Adding too much water will reduce the strength of concrete and may lead to cracking.
The ratios here should be used as a guide. Consider how deep your concrete will be, whether it will be exposed to the weather, and how much weight it will be supporting when deciding which concrete ratio to use. If in doubt, contact a professional.
How to measure quantities
Once you know the ratio of materials needed for your job, you’ll need to measure them out. You can measure materials by volume or weight. For a DIYer, it’s usually easier to measure by volume.
Using a separate bucket of the same size for each material is one of the easiest ways to measure the correct quantities. Although you can use a shovel, shovelling the same amount of material every time can be difficult. For this reason, a bucket will usually be more accurate.
Concrete additives
Additives can be added to concrete to improve the workability of the mixture, improve setting times and reduce shrinking or cracking.
Plasticisers
Adding plasticiser to concrete will make the mix more pliable and easier to work with. As with all additives, getting the correct dosage is crucial so always follow the product instructions to ensure accuracy.
Accelerators and frost-proofers
Accelerators and frost-proofers reduce setting times in cold conditions.
Concrete fibres
Concrete fibres are formulated to reduce cracking and shrinkage in concrete and mortar. Ideal for floor slabs, pathways and drives.
What is the role of each material in a concrete mix?
Cement
Cement is a fine powder that binds the other materials together.
Water
Water activates the cement, causing it to bind the aggregates and sand together. Too much water will make the concrete weak, and using too little will make the concrete hard to mix and work with.
Sand
Sand fills the gaps between large pieces of aggregate in a concrete mix to add strength and improve workability.
Aggregates
Aggregates improve the strength of a concrete mix and help prevent cracking or shrinkage.