Probably concrete block have been responsible in a greater measure than any other use of concrete for the popularity of concrete construction. Unfortunately, however, many of the early concrete block made were poor imitations of stone face and still poorer examples of concrete. The trouble lay largely in the fact that those who made them had little or no knowledge or regard for good concrete practice. Too little cement was used, the materials were not correctly proportioned, and so little water was used that the blocks were soft and porous.

Block Machines

Concrete block are best made in some one of the commercial machines intended for that purpose. A type of machine should be used that will permit of just as wet a concrete mixture as possible, otherwise there will not be enough water in the concrete to cause it to properly harden. Desire to turn out a large output tempts many persons to use too little water in the concrete. The mixture is barely more than damp while it should be wet enough so that when a handful of the mixed concrete is squeezed, a few drops of water will trickle from it.

Mixture To Use

Depending somewhat upon the character of the aggregate, concrete for the body of block should be mixed in the proportions of 1 sack of Portland cement, 2 1/2 cubic feet of clean, coarse sand graded in size up to 1/4 inch, to 4 cubic feet of hard pebbles or broken stone ranging from 1/4 to 3/4 or 1 inch. When the block are faced, the facing mixture should be in the proportions of 1 sack of Portland cement to 2 cubic feet of sand or whatever other material, such as crushed granite, marble chips, etc., is used as aggregate. Block having very pleasing texture surface finish can be made by following the practices outlined elsewhere in discussing surface finishes of concrete. It is important that block and similar products be properly hardened, and steam hardening or curing, which is explained in another section, is best.