- 1). Drive in two construction stakes that are parallel to the footings at the corner of the wall. Nail a third stake between the two stakes. These stakes are called batter boards. Tie a piece of construction twine to them that represent the exact outside edge of the block foundation. The batter boards need to be placed at least 2 feet away from the edge of the footing. This gives room to work without bumping the twine. Set up the adjacent corner at this time. Make sure that the corner is square before laying the CMU block.
- 2). Drop a plumb line down from where the two pieces of construction twine intersect. Additionally, drop a plumb line from each end of the wall. This plum line marks the exact location of the corners of the foundation wall.
- 3). Lay out a dry course of CMU block along the entire length of the wall. Use corner block CMU at each of the corners. Turn the last block 90 degrees to start the next wall. Use a scrap piece of plywood to space between each block. The plywood is the same thickness as the mortar joint. Determine what blocks need to be cut. If you have an interior CMU block wall that butts into the one you are working on, put a corner block at 90 degrees into the course of the wall where the interior wall is to be located. This determines what blocks need to be cut and where the cuts need to occur.
- 4). Mark the center of the CMU block cavity to indicate where steel rebar needs to be added per the architectural detail drawings. Use a marker for this step. Move the CMU blocks out of the way and place them outside of the footings, so there is room to start work.
- 5). Drill and epoxy in steel rebar that will connect the foundation to the CMU block wall. Refer to the architectural drawings for this detail, which will call out the size and spacing of the rebar. Use a hammer drill and epoxy to attach the rebar to the foundation.
- 6). Set the corner block into mortar at both ends of the wall. Check that they are plumb and level both horizontally and vertically. This is extremely important to get them positioned correctly. The rest of the blocks align with the corner blocks.
- 7). Pull a piece of carpenter's twine between the outside edge of the two corner blocks. This provides a line to lay the CMU blocks against as the blocks are laid between the corners.
- 8). Apply a layer of mortar onto the foundation that is 1 inch deep, 8 inches wide and 6 feet long using a spade trowel. This is enough mortar for three CMU blocks. Work from one corner down the entire length of the wall. The CMU block is already cut and ready to install from Step 3.
- 9). Trowel mortar onto one end of a CMU block. The mortar joint should be 3/8-inch thick between blocks. Set the block into the mortar on the footing. Level and adjust the CMU blocks, so they are even with the carpenter's twine and level across the top. Scrape the mortar joint even. A 4-foot carpenters level works perfectly for this. Fill the CMU block cavities with mortar that have rebar sticking up through them.
- 10
Repeat step 9 for three layers of CMU block. Rotate the corner block on each row. This will stagger the CMU blocks between rows. Move the construction twine up for each new row. Add CMU block wire every three rows in between the row of blocks to tie them together. - 11
Lay the last row of CMU block using header blocks. A header CMU block has a groove in it to lay rebar and is sealed on the bottom. This allows the block to be filled with mortar and add structural steel to connect the whole CMU block foundation together. Add anchor bolts in the mortar as required per the architectural details.
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