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Made from limestone or chalk and clay, cement provides the adhesive component in concrete and mortar. It binds the other components - aggregate and sand - together and dries to a very hard finish. The most common form of cement is Portland Grey but there is a lighter variation called Portland White. Cement is sold in 25kg (55lb) or 50kg (110lb) bags.
For repair jobs fast-setting cements are available which set hard in about 30 minutes. Another variation is sulphate resistant cement. This is used when the ground the mixed concrete is coming into contact with has a high clay content or is high in sulphates. Cement, whatever the type, must be stored somewhere dry as it will set rock hard if it gets damp or wet and will be unusable.
Plasticizer is available in powder form but is generally supplied as a liquid. It eliminates the use of lime when mixing mortar, while making the mix easier to work. Mixing instructions will come with the plasticizer (usually on the label), which will include the correct quantity to add.
Powdered pigments that can be added to the mix to permanently change the colour of the mortar, rendering concrete or pointing.
The following mixes give the quantities 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 plasticizer if you prefer.
General-purpose mortar for laying bricks, blocks and pointing:
For laying paving stones and patio slabs:
Concrete for foundations for an extension:
Concrete foundations for garden walls:
General purpose concrete for a base for slabs or a garden shed:
Alternatively, another general-purpose concrete mix is:
Render mix for an undercoat for plaster or an exterior coating:
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