Cement and water alone are known as " neat" cement, and are seldom so employed except where economy is not considered, or for purposes of maximum strength.

For most purposes a mixture of sand, broken stone, and cement gives ample strength, and is far more economical than the use of cement alone.

The following table of parts by volume, gives various concrete mixtures:

No.

Portland Cement.

Sharp

Sand.

Broken Stone.

Uses.

1

1

2

4

Highest grade of miscellaneous work.

2

J

3

6

For largest building foundations.

3

1

4

8

For ordinary construction.

4

1

4

10

For economical construction.

In these mixtures, the broken stone merely fills space, and if not available, the proportions of cement and sand should remain as given.

The sand also fills space, saving cement, and for strength it is essential that enough cement be used to surround entirely each grain of sand and thus form a perfect bond between cement particles. Broken stone and sharp sand present corners and angles for the better attachment of cement, as claimed by some users, but beach sand, the grains of which have been washed round by the sea, and rounded pebbles, are also frequently used with cement.