How to Work With Concrete Masonry Units

Measure the width and length of the wall. Place a concrete masonry unit at each end of the wall. Drive in stakes on both sides of each end block -- at least 1 inch out -- to mark the foundation width. String mason’s line between both stakes on each side to guide your digging.

Dig down past topsoil to mineral-rich subsoil, sometimes a mixture of sand and clay. If topsoil is thin, make sure the trench is at least 6 inches deep. Measure trench depth occasionally to make sure the foundation is even.

Fill the trench evenly with road base in 3-inch layers. Tamp each layer. Keep adding road base until, with a concrete block placed inside, just less than half its height extends from the top of the trench. Add 1 inch of stone dust to firmly set the blocks.

Mix the mortar according to the product instructions. Place dry mortar in the wheelbarrow and add minimal water. The consistency should be like whipped cream -- not soupy but also not too stiff and dry.

Place some mortar on the mortar board. Add about three-eighths inch of mortar to one end of the first concrete masonry unit using the trowel. Place this block at one end of the wall, in the center of the trench, with the mortared side facing the length of the trench. Make sure it is level in all directions. With the mallet, tap it into place.

Apply mortar to one end of the next concrete masonry unit and butt it up against the first, checking for level and tapping it into place. You want wall joints to be three-eighths inch thick in all directions, though you can make joints thicker to make blocks line up correctly. Continue in this way to place the first course of concrete blocks.

Lay mortar across the top of the first row. As suggested by the Arizona Masonry Guild, first scoop up a small amount of mortar. Place the trowel point on the block surface and then rotate the trowel 180 degrees -- moving your hand backwards in the direction you’re laying mortar to release and place the mortar.

Place the next and following rows the same way as the first, but stagger the rows so each new concrete masonry unit straddles the two below it -- covering half of one block and half of the adjacent block. Press down on blocks firmly to create a good bond.

Make half-blocks for short row ends by thickly scoring a block with the mason's chisel. Split the block along the score with the chisel. Smooth split edges with the brick hammer’s claw end.

Finish the garden border wall by applying mortar to the top row and then place the capstones. Check them to make sure they are level. Allow the mortar to dry fully before completely filling and tamping the trench.