Concrete, now so much used in forming the foundations of buildings of every description, and even the walls themselves, is a mixture of cement and sand, gravel, broken stones, brick rubbish, or similiar materials in the proportion of one part of cement to five or six parts of any of the other ingredients that are used in its manufacture. Good lime is often used instead of cement, but the amateur, if he uses lime at all, is advised to use cement with it in equal parts. The cement, being the substance that binds the gravel ballast, etc., together into a solid mass impervious to water, is technically called the matrix, and the substance that is added to the lime is called the aggregate.

It may be said that any waste material of a hard nature may be used as aggregate in making concrete, sand and gravel of all kinds, including pea or fine gravel, pit gravel, river gravel, ashes, cinders, and coke, lime chippings, flints, old stones and bricks, especially when broken, broken earthenware and stoneware, and rubbish from the brickyard may all be used. Slag, too, the refuse of the iron furnaces, can be made available whenever it can be obtained. It should not be used in too large sizes. Pieces about the size of stones ordinarily used for mending roads, or such as will pass through a ring of 2 inches in diameter, are best suited for the purpose when the material is broken up on purpose for making concrete.

Any of the various cements in general use may be used in the manufacture of concrete, but the amateur is recommended in all cases to use Portland cement.