The quantity of water used in mixing has a very great influence on the strength of the concrete. An excess of water weakens the concrete, while an insufficient amount prevents thorough mixing.

Therefore, only sufficient water should be used to produce a workable or plastic mixture.

Recent tests have proved that to secure the greatest strength the concrete should be mixed considerably drier than has heretofore been customary. Of course, for thin walls containing closely placed reinforcement, or for water-tightness, a fairly wet mix is necessary. A little experience will show the proper amount of water to use.

A very rough estimate of the quantity of water required in mixing for general work is 4 to 5 gallons to each sack of cement.

Three degrees of consistency (corresponding to different proportions of water) are used in general practice, namely, wet, medium, and dry. In the light of recent investigations it is thought the wet mixture of present-day practice contains too much water. The following definitions are therefore recommended:

Wet mixture. One that does not flow readily and yet can not be piled up. It is recommended for thin sections when reinforcement is closely placed.

Medium mixture. One that is between the wet and dry mixture. This consistency is recommended for general work.

Dry mixture. One about like damp earth. If a handful is squeezed it will retain its shape. This consistency requires thorough ramming to eliminate voids and is used when forms are to be removed immediately, but should not be used where a water-tight job is expected. The porous structure of the concrete in Figure 2 is due to the fact that it was placed as a dry mixture.