The present invention relates to building blocks and, more particularly, to interfitting construction units, or blocks, of precise height for constructing walls and buildings without mortar in the bed joints.
Walls and buildings constructed of, for example, concrete blocks require mortar at the bed joints, the horizontal interfaces between the blocks, in order to provide a level horizontal surface for each course of the blocks. This is due to the fact that concrete blocks and the like are manufactured in such a manner that the height of the blocks, from block to block and within each block, lacks adequate uniformity and precision. Most of the cost in constructing a wall of concrete blocks is in the labor needed to construct it, and it has been estimated that using mortar at the bed joints and levelling the blocks to make the horizontal surfaces of each course level and even accounts for about 70% of the labor cost.
Concrete blocks are made by filling a mold with concrete such that the bottom (or top) of the block, as the block will be positioned in the mold, coincides with the bottom of the mold. Then, the bottom of the mold is moved downward from the rest of the mold, and the block is moved downward with the bottom of the mold until the block is free to be moved off the mold bottom. This is done every 6 to 7 seconds. With this standard method, there is very limited uniformity and precision in the height dimension of the resultant blocks. Industry standards require only that there be no more than 1/8 inch, that is, + or -1/16 inch, variation of the height dimension in a block.
Without mortar, that is, with the blocks contacting the blocks of adjacent courses, at least portions of courses would not be level, and some of the blocks of a particular course would be higher than other blocks in the same course. In addition, due to such unevenness, there is misfitting of the blocks, which results in stress concentrations and, sometimes, failures. Also due to the unevenness, structures supported by such courses, such as beams, are contacted by only a portion of the area of the course which should contact the supported structure. There are spaces between the supported structures and other portions of the upper course which should contact the supported structures. As a result, stress concentrations are created in the course and in the supported structure, and the course or the supported structure sometimes fails.