Always use a gauge box to make sure of the right quantities when mixing large amounts of sand and cement. Measuring- quantities with a shovel or a bucket is a perfectly adequate way of tackling small tasks – but not for large ones. If each mix is not made up to the same proportions when laying a concrete path, for instance, the concrete may well dry out in a series of different shades – usually because more sand has been added to one mix than to another.
Make the gauge box by simply nailing and gluing lengths of 12mm 1 in plywood together, and. So that the sand can be tipped out easily, fit it with two handles shaped from 75 mm 3in by 25 mm 1 in timber. Make sure that the inside height of the box is 450 mm 18in and that the inside base is 300mm 12in square. This means that the box will hold .042cubic m of sand when it is full.
As a useful addition, make a false bottom that can be dropped into the gauge box should only .028 cubic m of sand or cement be needed. The bottom should be 150mm deep and should be fitted with a handle so that it can be removed easily.