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How to Cast Ready-Mixed Concrete in a Patio

Ready-mixed concrete is one of the most versatile building materials available to the handyman. Not only is it an essential ingredient of many building projects, in the form of strip or raft foundations set in the ground to support walls and other struc¬tures. It is also a constructional material in its own right, and can be used to create many outdoor features such as patios, paths and driveways.

The main drawback with concrete is without a doubt its appearance. This obviously does not matter when it is used for something that is largely hidden, such as a foundation slab, but where the material is on show its looks become more important. There are two ways in which the appearance of large expanses of con¬crete can be significantly improved; color and surface texture.

Color can be affected to a certain extent by careful choice of the sand used as part of the formula, and more drastically by the use of pigments, while the finish given to the slab can add a strong element of visual interest to the project.

In principle, laying concrete in the form of a patio, path or driveway differs little from casting a slab foundation. However, there are several specific points to bear in mind over and above the straightforward casting technique.

Firstly, order all the ready-mixed con¬crete you need for the job in one delivery. If you use several batches of concrete for a large project, slight differences in shade will be impossible to correct.

You may want to create shapes rather more elaborate than straightforward rec¬tangles and squares. Fortunately, con¬crete can do this easily so long as you are prepared to spend some time setting out the formwork in the shape you require.

As you plan the layout of your project, watch out for obstacles such as manhole covers and drainage gullies. You will need to plan the levels of your new surfaces carefully unless you are willing to move or reposition the obstacle.

Large areas of concrete cannot be laid as continuous slabs, or they will crack due to expansion and contraction. This means dividing the work up into bays, each separated from its neighbor by an expan¬sion joint of hardboard or bituminous felt if the concrete is laid as a continuous operation. If it is laid in alternate bays, board or felt joints are not needed; a simple butt joint will suffice.

- When the delivery arrives, try to have it delivered direct to where it is needed via the chute on the delivery lorry.
- Use barrow to transport loads to areas the chute cannot reach. Protect glazed doors with a sheet of hardboard.
- Spread the concrete using a garden rake and a shovel. Work it well into the sides and corners of the formwork to avoid hollows.
- Cast the slab in easily managed bays no more than 10ft long and compact the mix down well with a tamping beam.
- Lay the next bay in the same way, finishing off with a sawing to-and-f ro action of the beam to level the surface of the slab.
- When you have compacted the slab, apply the finishing texture. For a smooth, polished surface use a steel float.

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