Use as much water as possible without causing the blocks to stick to the plates or to sag out of shape on removing from the machine.
The amount of water required to produce this result varies with the materials used, but is generally from 8 to 9 per cent of the weight of the dry mixture. A practiced blockmaker can judge closely when the right amount of water has been added, by squeezing some of the mixture in the hand. Very slight variations in proportion of water make such a marked difference in the quality and color of the blocks that the water, when the proper quantity for the materials used has been determined, should always be accurately measured out for each batch. In this way much time is saved and uncertainty avoided.
Facing.
Poured Work.
Mixing.
The materials should be mixed dry, until the cement is uniformly distributed and perfectly mingled with the sand and gravel or screenings; then the water is to be added and the mixing continued until all parts of the mass are equally moist and every particle is coated with the cement paste.
Concrete Mixers.
Concrete Block Systems.
There are two systems of block making, differing in the consistency of the concrete used:
1. Blocks tamped or pressed from semi-wet concrete, and removed at once from the mold.