The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
First Aid For The Ailing Houses
Proportioning should be for the character of the work in hand, varying from a mass intended only for weight or to resist crushing, for watertightness, and for strength in a thin sheet. The difference in character will depend on the proportion of cement in relation to the sand and stone; the higher the proportion of cement, the stronger and more watertight the concrete will be. Concrete with a high proportion of ce- ment can be used for any purpose; but because cement is higher in cost than the other materials, the use of more than is needed will be wasteful.
The amount of water used should be in proportion to the cement; sand and gravel are used according to the stiffness or "sloppiness" necessary for pouring, troweling, or other handling of the wet mixture. Less water is used for strength, density, and waterproofness than for weight and resistance to crushing. When concrete for work of any importance is mixed, a trial batch should be made with the correct amount of water for the cement; should the mixture be too sloppy for the purpose, sand and stone are added to bring the mixture to the necessary stiffness, the proportions for the final mixture being made accordingly. Should the trial batch be too stiff, the quantities of sand and pebbles for the final mixture should be reduced.
As sand usually carries moisture, this must be allowed for; less water should be used for wet sand than for sand that is only damp. Sand so dry that it runs freely is rarely available. Sand is called "damp" when it feels so to the touch but leaves little moisture on the fingers; it is called "moist" when it leaves moisture on the hands; it is called "wet" when it drips. These three states are considered in Table I, Recommended Proportions for Concrete.
Mixing should be on a tight floor or on a platform made of tightly fitting boards; for small jobs around a house this can be 6 feet square. The measured amount of sand is spread and covered with the measured cement; the pile is then shoveled until the mixture is of an even color. Streaks of sand or cement show incomplete mixing. The mixture is covered with the measured stone or pebbles, and mixing is continued until this is evenly distributed. The middle of the pile is then hollowed, and the measured water poured in while the materials are being shoveled.
The mixture is shoveled or hoed until sand, pebbles, and cement are thoroughly and evenly combined. The concrete should be used within 30 minutes after completion of mixing.
