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Using concrete

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Using concrete

There is no need to rush laying concrete. Allow time to do the job properly, but go straight into the work after mixing. If concrete dries too quickly it may eventually cause cracks - therefore always aim to use within two hours and discard any left after that time. Polythene sheeting should be laid over concrete to allow for slow drying. Full drying and hardening will take from four to ten days, according to atmospheric conditions.

Concrete does not wear well in thin sections. In the long run it may be better to increase the area in need of repair, so as to allow for a thicker layer of concrete.

There are several trowels available, but most repairs can be carried out using a small diamond-shaped pointing trowel.

Repairing cracked concrete

Repairs to cracks may be improved with a PVA adhesive. Put the adhesive directly into the crack and leave to dry. Mix a small amount of the adhesive with the sand and cement mix.

In a simple crack with fairly sharp edges, filling alone should be sufficient, but if the edge is worn away, the ragged edge of the new concrete could crumble after a short time. To avoid this, use a cold chisel to chop into the old concrete, making a recess with clean angles. Poke out all loose material with the trowel or a spike and use a stiff bristle brush. Prepare a mixture using cement and sharp sand in the ration 1 part:3 parts respectively. Brush water into the crack just before you start to work. Using the point of the trowel, force the concrete as far into the crack as possible. Keep pressing it down and work in more until full, then level with the trowel.

Concreting a path

If concrete is to be laid to extend a path, measure and mark the area first. Dig out the path area to a depth of approximately 175mm (7 inches), to allow for a strong hardcore foundation and a good thickness of concrete. Use pieces of wood to a depth of 175mm (7 inches) to mark the boundary and restrict the new concrete. Once complete, the surface can be levelled with a straight-edged board moved up and down over it and the border. The path is only as strong as the base beneath it. In a garden the weight on a path is not as great as an area used to support the weight of a car.

Use hardcore on the soft ground for a sound foundation. Use up to 100mm (4inches) of hardcore below the concrete surface. Use broken bricks, blocks or stones which must be rammed down and crushed. Use a thin layer of ballast to fill in the gaps and ram the surface again, or use a garden roller. For larger areas it is possible to use a plate vibrator, which can be hired - see , to make the hardcore surface firm and sound.

Mix the concrete and lay 75mm (3 inches) thick. Push the concrete firmly against the wooden edges. Use the back of a rake to drag the concrete across the surface, making it a little higher than the wooden edging. Make sure that all the edges are filled and the surface is free of air pockets, which would weaken the surface.

Use a baten across the path and compact the concrete by chopping the surface as you draw the baten slowly over it. This can be moved backwards and forwards over the concrete, but do not work it excessively. If any areas need more concrete, shovel some more cement over the surface and work it into the rest. Leave the wooden boundaries in place until the concrete has set.

Finishing the surface of concrete

To achieve a smooth surface, use a float, which is a flat piece of wood or metal with a handle. Give a final tamp over the surface and draw the float across the surface simultaneously. Use a plasterer’s trowel to skim the surface for a smoother finish.

A broom head can be used to give a brushed finish. Angle the broom head as it is drawn across the surface, so that it indents the surface but does not pull it apart.

A length of scaffold pipe can be used to give a stipled finish. Roll the pipe over the surface using the same movement as a rolling pin.

Use a shovel or a float to make circular movements across the surface for a fish scale effect.

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