=21.= Concrete building blocks usually present about 2 square feet of
surface in the wall and are generally 8 inches thick, thus making a
volume of 1⅓ cubic feet. Since one-third of this volume as a rule is
air space, the actual volume of concrete is a little less than 1 cubic
foot. The materials in a block of this kind, if used in a 1-4 mixture,
will cost about 18 cents. If the block is 12 inches thick instead of 8
inches, the materials will cost about half again as much, or 27 cents.
The cost of labor to manufacture these blocks depends on whether they
are made in great quantities, and the wages paid the workmen, etc.,
and varies from 6 to 10½ cents for each block. To lay a block in the
wall costs from 5 to 10 cents, 7 cents being about the average price.
This price includes the mortar used in laying. For teaming and haulage,
an allowance of 5 cents per block is usually sufficient. The cost per
block, 8 inches thick, set in the wall is then as follows:
MAXIMUM COST MINIMUM COST
CENTS CENTS
Materials 18 18
Labor 10½ 6
Placing 10 5
Haulage 5 none
------ ----
Total 43½ 29
These results divided by 2 will give the cost of the wall per square
foot, since each block is supposed to have a surface of 2 square feet.
If the wall is 12 inches thick instead of 8 inches, one-half as much
again should be added to the price.