This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
Concrete blocks can be sold and laid up at a good profit at 25 cents per cubic foot of wall. Common red brick costs (at this writing) generally about $12 per thousand, laid. At 24 to the cubic foot, a thousand brick are equal to 41.7 cubic foot of wall; or, $12, 29 cents per cubic foot. Brick walls with pressed brick facing cost from 40 cents to 50 cents per cubic foot, and dressed stone from $1 to $1.50 per foot.
The factory cost of concrete blocks varies according to the cost of materials. Let us assume cement to be $1.50 per barrel of 380 pounds, and sand and gravel
25 cents per ton. With a 1 to 4 mixture, 1 barrel cement will make 1,900 pounds of solid concrete, or at 130 pounds per cubic foot, 14.6 cubic feet. The cost of materials will then be:
Cement, 380 pounds........... $1.50
Sand and gravel, 1,500 pounds. .. 0.19
or 11.5 cents per cubic foot solid concrete. Now, blocks 9 inches high and 32 inches long make 2 square feet of face of wall, each. Blocks of this height and length, 8 inches thick, make 1⅓ cubic feet of wall; and blocks 12 inches thick make 2 cubic feet of wall. From these figures we may calculate the cost of materials for these blocks, with cores or openings equal to ⅓ or ½ the total volume, as follows:
Per cubic foot of block, ⅓ opening....................... 7.7 cts.
Per cubic foot of block, ½ opening ...................... 5.8 cts.
Block 8 x 9 x 32 inches, ⅓ opening....................... 10.3 cts.
Block 8 x 9 x 32 inches, ½ opening....................... 7.7 cts.
Block 12x9 x 32 inches, 1/3 opening.................. 15.4 cts.
Block 12 x 9 x 32 inches, 1/2 opening.................. 11.6 cts.
If one-third of the cement is replaced by hydrate lime the quality of the blocks will be improved, and the cost of material reduced about 10 per cent. The cost of labor required in manufacturing, handling, and delivering blocks will vary with the locality and the size and equipment of factory. With hand mixing, 3 men at an average of $1.75 each will easily make 75 8-inch or 50 12-inch blocks, with J openings, per day. The labor cost for these sizes of blocks will therefore be 7 cents and 10.5 cents respectively. At a factory equipped with power concrete mixer and cars for transporting blocks, in which a number of machines are kept busy, the labor cost will be considerably less. An extensive industry located in a large city is, however, subject to many expenses which are avoided in a small country plant, such as high wages, management, office rent, advertising, etc., so that the total cost of production is likely to be about the same in both eases. A fair estimate of total factory cost is as follows:
Material Labor Total
8 x 32 inch, ⅓ space......10.3 7 17.3 cts.
8 x 32 inch, 1/2 space.....".7.7 6 13.7 cts.
12 x 32 inch, ⅓ space......15.4 10.5 25.9 cts.
12 x 32 inch, 1/2 space......11.6 9 20.6 cts.
With fair allowance for outside expenses and profit, 8-inch blocks may be sold at 30 cents and 12-inch at 40 cents each. For laying 12-inch blocks in the wall, contractors generally figure about 10 cents each. Adding 5 cents for teaming, the blocks will cost 55 cents each, erected, or 27.5cents per cubic foot of wall. This is less than the cost of common brick, and the above figures show that this price could be shaded somewhat, if necessary, to meet competition
S. B. Newberry in a monograph issued by the American Association of Portland Cement Manufacturers.