Measure the water with a bucket. This will give more uniform results than using a hose. The number of gallons indicated in the tables is only approximate. Try it on the first batch; and if the mixture is made too wet, reduce the amount of water; if too dry, increase the amount, so as to get the desired consistency.
Suppose, for example, that we wish to con struct a silo. This calls for a certain amount of rich mixture 1:2:4 (see Table X). If a natural mixture of sand and gravel is not obtainable, we shall have to mix these ingredients our selves, possibly using crushed stone instead of gravel, and shall therefore have to use Table XI. If, on the other hand, a natural bank of sand and gravel is near by, we shall take our aggre gate from that, and in that case shall use Table XII.
Assume the latter case. We shall probably have first to screen out the excess of fine mate rial so as to get a well-graded aggregate, for natural mixtures ordinarily contain far too much sand or finer material. Then, simply turning to Table XII, we look for 1:2:4 under the heading "Mixture." Reading across toward
the right, we find under the heading "Quanti ties of Material Required," that we shall have to measure out cubic feet of the natural mixture of sand and gravel for every 2 bags of cement used. The next column shows that every such batch will give us cubic feet of concrete; and under "Size of Measuring Boxes" we learn that the mixed sand and gravel for a batch should just fill a box 2 feet wide, 4 feet long, and inches deep, inside dimensions. Ten gallons of water may be tried in mixing the first batch, but the quantity may have to be increased. This will depend somewhat on the way the aggregate is graded, and the amount of fine material present.
Possibly we may have figured out the num ber of cubic feet of concrete that will be required on a job, and our cement will be in barrels instead of bags. In that case, Table XTTT will be found useful, as it shows the quantities of cement and aggregates in one cubic foot of concrete of varying mixtures.