The mixing board should be located in convenient relation to the supply
of materials and the work and should be level. The sand box is placed
on the board, about 2 feet from one of the longer sides, and filled
level with sand; the box is then lifted away and the sand spread in a 3
or 4 inch layer. The cement is spread as evenly as possible on' top of
the sand. Two men with shovels, standing on opposite sides of the pile,
turn the sand and cement in such a way that the materials axe thoroughly
mixed. In turning the material it should not be simply dumped off the
shovel, but should be shaken off the ends and sides, so that the two
constituents will be mixed as they fall. The mass should be turned two
or three times, or until it is of uniform color and there are no streaks
of either sand or cement. A man with a hoe or rake may assist by raking
the top over as the two men turn. When the sand-cement mixture is of a
uniform color it should be spread out carefully in a layer and the gravel
box placed on top. The box is filled with gravel and then removed, the
gravel being spread over the sand-cement mixture. The mass is soaked with
about one-half the quantity of water to be used, care being taken not to
wash away any of the cement. The materials then should be turned over
in much the same manner as was the sand-cement, except that instead of
shaking them off the end of the shovel the whole load should be dumped
and dragged back toward the mixer with the square end of the shovel.
The wet gravel picks up the sand and cement as it rolls over when
dragged back. The mixing should be continued until the mass is uniform,
water being added to the dry spots during the mixing until the desired
consistency is obtained.
Experience counts considerably in mixing concrete with the least amount
of labor; ordinarily three or four turnings are required to mix the
materials thoroughly. After the final turning the concrete should be
shoveled into a compact pile and then is ready for placing in the forms.