Concrete is a mixture of cement, sand, gravel and water. Variations in the ratio of the ingredients produces a mix suitable for different jobs but we will be instructing you on a general purpose mix suitable for most garden tasks and shallow foundations – not house foundations.
Mix 1 part cement, 2 parts sand and 4 parts of gravel. What you use to measure the parts depends on how much concrete you need – normally buckets are the best measure, one part being a level bucket full. Adding water is not a simple matter as the sand you are using might already be wet. So use trial and error – add some water and mix until the consistency is right. How do you know – well a shovel full will stay in a loose heap and not slop over the edges but the mix is soft enough for you to smooth and shape easily.
What ever you are applying the concrete to should be wet as this helps the concrete bind to it.
The mix dries and hardens – but if it the conditions are too hot the mixture will dry unevenly and crack. So if the concrete is in full sun on a hot day cover it will some shade – plastic or a sheet, to slow down the drying.
As the mix dries, it will harden. But the drying, or ‘curing’ should be gradual, otherwise cracking may occur. To prevent cracking, plastic is placed over the curing concrete to trap the water inside, ensuring gradual curing.”
If you are mixing a lot of concrete it pays to hire a cement mixter as it is back breaking work. Also getting an even mix is really important for producing strong concrete.
Concrete contains cement plus sand and gravel. So do not make the mistake of buying bags of cement and just mixing with water – the mix will not be strong and may just powder when dry.