Pouring foundation concrete.

Preparation: It is important not to leave the foundation trenches open for too long before they are filled with concrete. In our climate, heavy rainfall can cause the sides to collapse or slide into the trench, or vandals or simply inquisitive passers-by can help to collapse the sides also by walking too close to the edges. In either case any debris that has fallen into the trenches will have to be shovelled out manually before the concrete is poured. If heavy rain has fallen, you may also have to hire a water pump to get rid of any accumulated water. Both are jobs to be avoided if at all possible.

Assuming all is well and your foundation trenches are intact and clear of fallen debris, you are ready to pour the concrete. Shortly after the trenches have been dug and building control has approved them your local pre-mix concrete plant should have been contacted and a mutually convenient time arranged for delivery.

Timing deliveries of pre-mix concrete: It is important to get the timing of this task right. If you need 30 cubic metres of concrete you do not want five lorries arriving all at once. They won’t have room to all get on site at the same time and, unless you have a lot of money or a lot of friends, or both, you will not have the manpower to pour such a large amount.

Having the pre-mix lorries arriving at half-hour intervals is a sensible option. Depending on the proximity of your site to the pre-mix base the job can be handled by one lorry or several. The pre-mix operator will schedule deliveries as efficiently as possible.

Pouring: Usually, and if your site has been properly laid out, the concrete can be poured straight from the lorry into the foundation trenches. If certain parts are inaccessible then a pump, digger, dumper or some other machine should be on site to transfer the concrete from the lorry to the foundation trench. Once in the trench the concrete should be tampered to help it to settle and, where the traditional method is being used (see below), it should be poured to the level of the top of the pegs that were put in place when the foundation trenches were dug.

Recently we have seen the introduction of self-levelling, or self -placing, concrete. As the name suggests, this finds its own level throughout the foundation trench system and obviously reduces the need for additional labour or the additional machinery required to transfer the concrete to inaccessible areas.

Whatever type of concrete is used there are two methods of laying foundations.

Traditional laying of founds: In the first, the traditional method, the minimum amount of concrete is used, poured only to the depth of the pegs used when levelling the foundation trenches. This will be a minimum of 250mm. Bricklayers are then required to lay blocks to build the footings up to sub-floor level.

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