Concrete blocks are designed to be laid in a running bond (sometimes called a half-bond) pattern in which the vertical joint of two adjoining blocks falls over the center of the block below. If you have control over design decisions, lay out the distances between corners and bump-outs, as well as the dimensions of door and window openings, in 8-inch or 16-inch increments to match the full- and half-length blocks.
Corners are a key detail in a block basement, and must be built to maintain a modular layout. Here are some key points to keep in mind:
1. A running bond starts from the corner with each course offset by half a block from the one below it. By building up the corner first, a mason can establish the course heights and the plumb of the wall.
2. If blocks must be cut, maintain a running bond by staggering the cut blocks symmetrically. Joints as close as 4 inches from a joint in the course above and below will not affect the strength of the wall, but the appearance will suffer if the joints are off-center. Where portions of the wall will have the cores filled with concrete, keep the half-bond dead accurate.
3. Wall intersections add strength to help resist soil pressure. Buttresses or “wing walls” can be built to stiffen main walls, even if no partition is necessary. Weave alternate courses in wing walls together as in a corner, and grout all cores and reinforce with steel.
The use of 8-inch block simplifies corner construction because weaving the block at corners establishes the running bond and keeps the cores in a two-core block in line. With 10-inch and 12-inch block, a number of techniques can be used to lay out corners; the simplest method uses special L-shaped corner block.
