If four men are available, it is best to increase the size of the batch mixed to a four-bag batch, doubling the quantities of all materials used. The cement board should also be increased to 10 by 12 feet as shown under “Tools.” In this case start the mixing in the middle of the board, and each pair of men mixing exactly as if for a two-bag batch, except that the concrete is shoveled into one big mass each time it is turned back on to the center of the board. When more than four men are available, the rest may place the concrete, make new runs, load wheelbarrows, etc., taking the concrete away from the board as fast as it is mixed. In this case another small concrete board should be placed next to the big “board,” so that in the last turning the batch can be shoveled over on to the small board for placing, making room on the big board to mix the next batch. The small platform need be only just big enough to hold the pile of mixed concrete.

How to Determine Quantities of Materials Needed

First figure the number of cubic feet of concrete that will be required for the work in question. Then by multiplying this number by the number under the proper column and required mixture shown in [Table III], the amounts of cement, sand, and stone or gravel can be found.

TABLE III.

Mixture. Quantities of Material in 1 Cu. Ft. of Concrete
Cement,
Barrel		Sand,
Cu. Yard		Stone or Gravel,
Cu. Yard
1 : 2 : 4 Concrete.058.0163.0326
1 : 2½ : 5 Concrete.048.0176.0352

Example

Suppose the work consists of a concrete silo requiring in all 935 cubic feet of concrete, of which 750 cubic feet is to be 1: 2: 4 concrete, and 185 cubic feet is to be 1: 2½: 5 concrete. Also enough sand and cement is needed to paint the silo inside and outside, in all 400 square yards of surface, with a 1: 1 mixture of sand and cement. One cubic foot of 1: 1 mortar will paint about 15 square yards of surface and requires 0.1856 barrels of cement and 0.0263 cubic yards of sand.

Solution, Etc.

Thus the necessary quantities of materials are:—