Step-by-step: How to build a block counter
Snap chalk lines that are a consistent distance ― 1 or 2 inches ― from each side of the blocks.
Use a pencil to mark the openings exactly, then double-check that the openings are the correct width. Use a framing square to check the corners. Dampen the slab.
Mix a batch of mortar and spread a layer about ½ inch thick in between the layout lines.
Press it into place so that the mortar is about 3⁄8 inch thick. Check the block for level in both directions and check the face of the end for plumb. Scrape away excess mortar and use it for the next block.
For a short wall like this, simply set the blocks in order.
Scrape mortar onto the flanges of the laid blocks and set the next course of blocks on top. Start the next row with a corner block or a half block, so the blocks will be stacked one on top of two. Check this row for level and see that the blocks form a straight line. Scrape mortar from the joints as you work.
Do this every other course.
Install the intervening blocks so they nearly touch the line. The line can serve as a guide for level as well as straightness along the wall’s side.
If you need to cut a block, cut the next-to-last block and then install a full-sized closure block. Spread a thick layer of mortar onto both ends of the closure block. Align it precisely with the center of the opening and carefully slide it straight down into place. If mortar peels off one of the ends, pick the closure block up, reapply mortar, and try again.
If that is not possible, use a circular saw equipped with a masonry blade to cut a channel that you can slide the lintel into. Mark and cut carefully so the angle iron will be level. The masonry saw blade makes a cut that is just thick enough for the angle iron.
Drill a hole for the conduit using a masonry bit. Draw a circle for the conduit's hole, drill six or seven holes along its circumference, then chip out the hole using a small masonry bit. Run conduit to the box using an elbow to make the turn. Tap in shims to wedge the box in place. Stuff newspapers into the cell about 6 inches below the electrical box, then fill the area around the box with concrete to hold the box firmly in place.