The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
First Aid For The Ailing Houses
Mortar is a mixture of portland cement, 10 per cent by volume of hydrated lime, sand, and water. Cement is a mixture of portland cement, sand, and water. Concrete is portland cement, sand, gravel (aggregate), and water.
The home owner may buy the portland cement, sand, gravel, and hydrated lime separately from a building-supply dealer and do the mixing himself. If this task looks too forbidding, he may buy his concrete ready-mixed from a contractor who specializes in delivering concrete to the site in huge mixer trucks that thoroughly combine the materials with water on the way to the job. This is an excellent method if the amount of concrete is large, for a driveway, a garage slab, walkways, foundations, etc. For smaller work, dry materials ready-mixed in the bag may be purchased from the buildingsupply dealer. This packaged concrete mixture, called Sakrete, needs only the addition of water to become ready for the job. It permits using small quantities for little jobs without buying loads of material.
Much of the space occupied by a mass of concrete is taken up by the aggregate; the spaces between the pieces of stone are filled with sand; the portland cement, being in the form of fine powder, fills the spaces between the grains of sand and all other cavities. Used dry, the stone or pebbles, the sand, and the cement will fill a space so completely that there will be no holes or cavities. When wet, the powdery cement will run together and in drying will harden into its original form of rock. The stone or pebbles will be bound into it so that the whole will form a solid and dense mass.
Because the sand and cement fill the spaces between the larger pieces, a mass of concrete will occupy less space than the spaces occupied by the three parts by themselves. For example, a common concrete mixture is 1 cubic foot of cement, 2 cubic feet of sand, and 4 cubic feet of broken stone or pebbles—in all, 7 cubic feet. When combined as concrete, the sand and cement will run into the spaces between the larger pieces, and the finished mass will occupy a space of only a little more than 4 cubic feet. This must be reckoned with in estimating the quantities of materials necessary for a required mass of concrete.
To develop full strength, density, and permanence, concrete must be correctly proportioned, mixed, poured, and cured; errors in any one of these steps will reduce quality.
