Using concrete in DIY projects can be strenuous work, but the principles involved are not complex. It is important to ensure that the correct percentages of cement, sand and stone are mixed with the right amount of water. Certain guidelines should be followed when laying concrete.
The proportions of cement, sand and aggregate (stone) used for concrete work depend primarily on the use to which the concrete will be put. Generally there are three grades of concrete - low strength, medium strength and high strength - although the actual ratios of the dry materials used will sometimes vary depending on the quality of the materials available. While low-strength concrete is commonly used for foundations and footings, a medium strength is preferred for garden footpaths, domestic driveways and steps, and for patio slabs that will be exposed to weathering. High strength concrete is really only necessary for watertight walls and industrial situations or driveways that will take very heavy traffic.
The main elements in concrete are describe below:
Cement - Cement is a very fine grey powder which, when mixed with water, creates a chemical reaction which causes it to harden. The cement need time to cure and set before it reached its full strength.
Sand - The best sand to use for making concrete are building sands with evenly graded particles of various sizes no bigger than 4.75mm and approximately 5% of the sand consisting of very fine material. Using the wrong type of sand will result in concrete that will be difficult to work with.
Stone - The coarse aggregate in concrete, is screened to size especially for construction purposes. Natural pebbles, pea gravel and crushed stone are available. For DIY purposes 20mm or smaller stone is ideal.
Mixing concrete is a laborious task. Even if you have a mechanical concrete mixer, you will still have to shovel the dry materials into the machine. Whether you are mixing by hand or machine, you will have to measure the materials in batches to ensure that the proportions used are accurate. A builders bucket or clean 25 litre paint tin are useful for measuring.
If you have a machine, load the aggregate with a little water first to prevent the mortar from building up on the blades, then load the sand and finally the cement and more water. When mixing by hand, combine the cement and sand first, either in a wheel barrow or on a flat dry surface. Do not mix them directly on the ground as soil, dead leaves and small twigs will almost certainly get mixed in, and water may be absorbed from the mixture. Make a crater in the centre, then add water, shovelling the dry mixture from the edge to the centre. Once it is smooth, add the stone and continue shovelling. Aim for a firm consistent mixture which is neither too runny nor too dry.
The proportions of cement, sand and aggregate (stone) used for concrete work depend primarily on the use to which the concrete will be put. Generally there are three grades of concrete - low strength, medium strength and high strength - although the actual ratios of the dry materials used will sometimes vary depending on the quality of the materials available. While low-strength concrete is commonly used for foundations and footings, a medium strength is preferred for garden footpaths, domestic driveways and steps, and for patio slabs that will be exposed to weathering. High strength concrete is really only necessary for watertight walls and industrial situations or driveways that will take very heavy traffic.
The main elements in concrete are describe below:
Cement - Cement is a very fine grey powder which, when mixed with water, creates a chemical reaction which causes it to harden. The cement need time to cure and set before it reached its full strength.
Sand - The best sand to use for making concrete are building sands with evenly graded particles of various sizes no bigger than 4.75mm and approximately 5% of the sand consisting of very fine material. Using the wrong type of sand will result in concrete that will be difficult to work with.
Stone - The coarse aggregate in concrete, is screened to size especially for construction purposes. Natural pebbles, pea gravel and crushed stone are available. For DIY purposes 20mm or smaller stone is ideal.
Mixing concrete is a laborious task. Even if you have a mechanical concrete mixer, you will still have to shovel the dry materials into the machine. Whether you are mixing by hand or machine, you will have to measure the materials in batches to ensure that the proportions used are accurate. A builders bucket or clean 25 litre paint tin are useful for measuring.
If you have a machine, load the aggregate with a little water first to prevent the mortar from building up on the blades, then load the sand and finally the cement and more water. When mixing by hand, combine the cement and sand first, either in a wheel barrow or on a flat dry surface. Do not mix them directly on the ground as soil, dead leaves and small twigs will almost certainly get mixed in, and water may be absorbed from the mixture. Make a crater in the centre, then add water, shovelling the dry mixture from the edge to the centre. Once it is smooth, add the stone and continue shovelling. Aim for a firm consistent mixture which is neither too runny nor too dry.