How to Construct a Cinder Block Basement

Snap a chalk line on the top of the footing to mark the front of the block wall on the footing. Allow at least 2 to 3 inches margin on both edges of the footing so that the block wall is positioned toward the center of the footing. Lay a "dry run" of blocks onto the footing without any mortar to determine the exact placement and number of blocks for the first course. Leave 3/8-inch space between each of the blocks to account for the mortar. Adjust the blocks and make any guideline marks on the footings if needed. Remove all the blocks.

Dump a bag of dry mortar mix into a wheelbarrow and add water. Mix the mortar and water with a hoe, stirring until the mortar mix resembles oatmeal. Do not add too much water to the mix or the mortar will not adhere to the blocks. To test for readiness, chop the mortar into ridges with the end of the hoe. If the mortar stays in place, the mortar is the correct consistency.

Scoop mortar with a trowel. Place two 1-inch thick, three-block long rows of mortar onto the chalk line on the footing about 7 1/2 inches apart, starting at one corner and working toward your left side. Grasp the first cinder block and place it firmly onto the mortar in the corner, aligned with the chalk line. The block should rest atop the two rows of mortar on the footing.

Apply a 3/8-inch thickness of mortar onto the side of the next cinder block at the outer edges. This process of adding mortar directly to the blocks is called "buttering." Place this block on the left side next to the first block and onto the rows of mortar on the footing. Repeat this process for the next block.

Use the level to check that the blocks are level and plumb. Add more mortar if the block dips. Tap the corner of a block that rises too high. Set the level on the footing and place the level against the backs of the blocks. Test for plumb and move the blocks if necessary.

Build up the corner of the wall in which you were working by creating another furrow of mortar on the right side of the corner where you began. Always maintain that the corners are at least one row higher than the other runs of the wall. Lay three or four blocks on your right side of the corner as you did for the first three blocks on your left side of that corner. Test the blocks for level and plumb.

Scoop more mortar and place it on top the first run of blocks you installed, starting in the corner and working along your left side. Stagger this second run of blocks by placing the corner block perpendicular to the block at the corner in the first run. Butter the blocks and lay them in place. Once you have two blocks on the second run on your left side, lay two blocks from the corner on your right side.

Trim off excess mortar from the front and back sides of the blocks with a V-joiner. Dip the V-joiner in water. Scrape the joints gently with the V-joiner, pressing firmly enough to create a concave joint in the mortar.

Continue laying blocks along your left side, down along the footing. When you get to the corner on the other end of the footing, build up the corner with another, second run of blocks. Work like this, placing blocks in staggered seams and in staggered heights all around the sides of the footer.

Lay metal lath or steel tie bars on the top of every other run. This thin metal reinforcement adds strength to the wall. To install, butter the tops of the blocks with 3/8-inch mortar and gently press portions of the lath or tie bars into the mortar. Place new blocks atop the existing run as normal.