To build a block wall, stack rows of interlocking retaining wall blocks on top of a layered base, and backfill the wall with crushed gravel for support. Contact a building code administrator to ensure the area is structurally sound and free of underground utility equipment.
- Dig a trench
For a 4-foot wall, dig a trench that is 7 to 9 inches deep and 24 to 28 inches wide. Set the soil aside for later use. Place a block at the front of the trench and a few inches back, and ensure there is at least 12 inches of open space behind the block.
- Flatten the base
Use a tamper to flatten the base.
- Mark the base for the layered materials
Attach a 4-foot level to a long 2-inch by 4-inch board. Start at the bottom and measure up. Measure the first 4 to 6 inches of the height of the base, and use the level and a stake to mark the top of the height. Measure 1 inch higher than the first stake, and use the level again to mark the height.
- Install a compacted base
Pour class V crushed base material in the trench. Tamp the base until it is flat and flush with the top of the first stake.
- Install a layer of sand
Pour sand on top of the compacted base. Use a screed board and a hand trowel to level the sand to the top of the second stake.
- Install the first brick
Lay down the first brick, and secure it with a 3-pound sledge hammer.
- Install the first row
Run a masonry string along the back of the first brick. Install the rest of the first-row blocks along the string. Ensure the row is level lengthwise by using a 4-foot level, and use a torpedo level to make sure the row is level widthwise.
- Install the soil
Pour the soil from earlier in front of and behind the first row. Pack the soil until it is ground level.
- Install the remaining rows
Lay the second row of bricks on top of the first row with a 3/4-inch offset from the front and a 4-inch overlap at the vertical joints. Hammer the pins into the holes, and hammer a center pin below the surface of the blocks. Repeat with the remaining rows.
- Fill the back
Pour crushed gravel in the space behind the wall until it is flush with the top row.
- Install cap blocks
Apply two lines of concrete adhesive on one of the top row blocks. Install a cap block on top of the block. Repeat with the remaining blocks of the top row.