Building a concrete block wall, whether for a foundation or a retaining wall, begins with the placement of a concrete footing that is poured separately and on which the block wall is built. The footing and block wall structure are linked together by installing incremental vertical reinforcing bar, commonly called "rebar," uprights installed as part of the footing's own reinforcing prior to pouring the footing concrete. The vertical bars are extended upward into the cells of the concrete blocks to bond the wall to the footing. Installation of the base rebar follows a standard methodology that can be adapted to any block wall construction.
Inspect the footing trench to verify that the footing form boards, if there are any, are properly placed and the required horizontal reinforcing steel bars have been installed. Building codes require that at least two equally spaced and parallel horizontal reinforcing bars are suspended in the footings and the vertical rebar uprights tied to these horizontal bars within the footing concrete. Codes vary based on the building site's soil conditions and the type of block wall being built.
Figure out the number of upright reinforcing bars you will need and the spacing required for the planned block wall. The typical upright spacing for a block wall of any height is 24 inches to coincide with the cell openings in the concrete blocks.
Lay out the spacing for the uprights on the footing form boards, using a pencil or carpenter's crayon. The uprights are positioned along the block wall center line; the marks on the form boards can be used as guides in spacing the upright reinforcing bars properly.
Cut a 4-foot length of rebar for each vertical upright bar, using a hacksaw.
Bend each length of rebar to create an "L" shape, with one arm of the angle 16 inches long and the other 32 inches, using a rebar bender. The rebar can be bent by hand, but benders create a much tighter angle that is less likely to interfere with the concrete blocks above them.
Hold the "L" shaped bar with the longer arm vertical and align with one of the layout marks. Secure the shorter arm to the horizontal footing rebar, using tie wire at both ends of the arm. Wrap a short piece of tie wire around both rebar pieces and twist the ends together until tight.
Repeat Step 6 for the rest of the rebar uprights.
Pour the footing concrete; allow the footings to fully cure before building the concrete block wall. Install the additional lengths of rebar where the vertical rebar uprights need to extend to the top of the concrete block wall. Lap the additional rebar to the adjacent bar for a minimum of 18 inches, and secure with tie wire.