If the trenches are not excavated to the neat size of the footings, or where the concrete is above the level of cellar floor, this contractor shall set up 2-inch plank, supported by stakes or solidly banked with earth to confine the concrete, and these planks are not to be removed until the concrete is (48) hours old.
The concrete shall be composed of first-quality fresh (Atlas) cement, clean, sharp sand and clean (granite) broken to a size that will pass through a 2½-inch ring, and thoroughly screened. These ingredients shall be used in the proportion of 1 part cement, 2 of sand and 4 of stone, and mixed each time by careful measurement, in the following manner: On a tight platform of plank spread four barrows of sand, and upon this two barrows of cement. Thoroughly mix the two dry, and then throw on eight barrows of broken stone and work over again; then work thoroughly and rapidly with shovels while water is being turned on with a hose, until each stone is completely covered with mortar. No more water to be used than is necessary to unite the materials. As soon as the concrete is mixed it is to be taken to the trenches and dumped in layers about 6 inches thick, and immediately rammed until the water flushes to the top. The next layer must be put on before the preceding one becomes dry, and the top be well wet before putting in the new layer. The stone footings shall not be put on the concrete until it is two days' old. (See Sections 140, 145.)
* This latter clause is not always required.
[On large and important work the specifications should also provide for testing the cement. (See Section 125.) The above quantities are as much as should be mixed at one time.]