Summary: Learn how to mix concrete, mix cement, the concrete mix for laying paving stones and patio slabs, the concrete mix for foundations for an extension, the concrete mix for foundations for garden walls, the general-purpose mortar mix for laying bricks and blocks.
Depending on the quantity required there are two ways of mixing concrete and mortar. You can either use a cement mixer which can be hired from a tool hire shop or you can mix up on a large board placed on the ground called a spot board.
Different jobs require different mixes and a selection of mixes with the ratio of ingredients is given below. Depending on the job you are doing you may need to include additional materials to give the mix a specific characteristic. These materials are lime, plasticiser, cement pigment, waterproofer and frost proofer. Some of these are quite self-explanatory, but they are all described in the materials section of this website under Cement, Aggregate and Sand.
Here we look at how to hand mix on a spot board.
Mixing by hand
- Position the spot board on the ground not too far from where you will be using the mix.
- Use a shovel to heap the ingredients onto the spot board in the ratio required for the mix. Do not overload the board.
- With the shovel, keep turning the heaped ingredients over to mix them thoroughly.
- When you are satisfied that the ingredients are well mixed, hollow out the centre of the pile.
- Pour enough water into the hollowed out centre to produce the correct consistency. This is not an exact science as the amount of water you add can depend on the materials you are mixing. For example, if the sand is wet from being stored outside, you will not need as much water as if it was dry. It is best to add the water gradually to avoid pouring in too much and making the mix too wet.
- With the water in the hollowed out centre, carefully push the sides into the centre with the shovel and begin turning the mix over until you have the correct consistency.
Concrete and mortar mixes
The following mixes give the ratio of cement, lime, sand and coarse aggregate for different types of concrete and mortar mixes used in DIY. The proportion indicates the ratio by volume, usually a shovel-load. However, if greater accuracy is required in the mixing to maintain the strength or colour throughout then it is best to use a bucket to measure out the quantities. In some of the mixes below we have included lime, but you can replace this with a plasticiser if you prefer.
General-purpose mortar for laying bricks, blocks and pointing:
- 1 cement
- 1 lime
- 5 builder’s sand
- Mix with water to produce a consistency that allows the mortar to stick to a trowel when turned upside down
For laying paving stones and patio slabs:
- 1 cement
- 4 sharp sand
- Mix with water to produce a consistency that is stiffer than the general-purpose mortar above
Concrete for foundations for an extension:
- 1 cement
- 2.5 sharp sand
- 3.5 coarse aggregate
- Mix with water to produce a consistency that pours easily
Concrete foundations for garden walls:
- 1 cement
- 5 ballast
- Mix with water to produce a consistency that pours easily
General purpose concrete for a base for slabs or a garden shed:
- 1 cement
- 2 sharp sand
- 3 coarse aggregate
- Mix with water to produce a consistency that should pour easily
Alternatively, another general-purpose concrete mix is:
- 1 cement
- 4 ballast
- Mix with water to produce a consistency that should pour easily
Render mix for an undercoat for plaster or an exterior coating:
- 1 cement
- 1 lime
- 6 plasterer’s sand
- Mix with water to produce a consistency that allows the mortar to stick to a trowel when turned upside down
Tools needed
- Shovel
- Cement mixer
- Bucket
Materials needed
- Spot board
- Lime or plasticiser
- Cement pigment
- Waterproofer
- Frostproofer
- Cement
- Aggregate
- Sand