Building a structurally sound concrete block column requires following a method used by professional block masons. Whether needed for a gate pillar or porch support, the procedure for a 16-by-16-inch square column can be adapted to any standard block size or column height by adapting the method to the various masonry unit sizes available. Local and national building codes have specific requirements regarding concrete block, footing size, reinforcing and load bearing. It is recommended that reinforcing steel uprights be placed in the slab or footings at the column locations when they are poured to provide an additional anchoring for the column structure.
Mark the center of the column location on the concrete slab or footing. Use a framing square to lay out the perimeter outline of the column with a pencil or carpenter's crayon.
Mix the concrete mortar according to the manufacturer's directions. Mortar should be mixed to a stiff yet moist consistency. Use a trowel to spread a 2-inch-wide-by-1-inch-high layer of mortar mix around the perimeter of the column outline marked in Step 1, just inside of the lines. Spread a similar layer of mortar through the middle of the column location, in one direction only, to provide a mortar base for the middle portion of the cement blocks.
Lower one concrete block into position over the rebar and onto the mortar. Using the side of the trowel blade or the end of the trowel's handle, gently tap the block into the mortar until there is an even mortar joint thickness of ? inch. Use a torpedo level to make sure the block is level in both directions.
Lower another block into the mortar base, next to and against the block set in Step 3. As with the previous block, gently tap the block into the mortar until there is a mortar joint thickness of 3/4 inch under the block and the top surfaces of the two blocks are flush. Use a torpedo level to make sure both blocks are level in both directions. The two blocks, side by side, now measure 16 inches square and form the basic shape of the column.
Collect the excess mortar that was squeezed out of the joints beneath the blocks and return it to the mixed mortar, using a trowel.
Spread an approximately ½-inch-thick layer of mortar over the top surface of the concrete blocks set in steps 3 and 4.
Lower a concrete block over the rebar upright and onto the top of the mortar. Position this block perpendicular to the previous layer of blocks and flush at the sides. Gently tap the block into the mortar until there is a mortar joint thickness of ? inch. Use the torpedo level to make sure the block is level in both directions.
Lower the adjacent concrete block into place beside the block set in Step 7 and level as described, maintaining the consistent ?-inch mortar joints.
Repeat steps 5 through 8 for each course of concrete block until the column is approximately 48 inches tall.
Mix the concrete mix according to the manufacturer's directions. The concrete mix should wet enough to pour from a bucket into the concrete block cells. Fill all of the block cells to level with the top of the column structure.
Repeat steps 6 through 10 until the desired column height is reached. Use a joint tool to smooth, or "strike," the mortar joints. Allow at least 72 hours before applying any loads to the new column.