Retaining Walls

Begin by staking out the wall. For curved sections, use a garden hose to lay out the wall line. Dig a trench along this line. The width of the trench should be twice the depth (front to back) of the block used. If block is 8 inches deep, make trench 16 inches wide. When using one, two or three courses of block, make the trench deep enough to bury half of the first course plus 2 inches of compacted base material. When using four or five courses of block, make the trench deep enough to bury the full first course plus 2 inches of base material. When using six or more courses of block, bury the full first course plus 4 inches of base material.

Remove loose soil and firmly compact the soil in the bottom of the trench with the tamper. Then place base material in the bottom of the trench. Base material can be paver base or an equivalent to ¾-inch minus (with fines) aggregate. Use the appropriate amount of base material for the number of courses you are building.

Add a 2-inch layer of base material, rake out and firmly compact with tamper. Level the surface from front to back and side to side. Check with a carpenter’s level, checking level every few feet. The more level the base material, the easier it is to level the block. Add another 2 inches of base if needed for the height of the wall (see Step 1).

Use a hammer and chisel to remove the rear lips from all blocks used for the base course. Use string to align the back edges of the first course. Position the wall units side by side on the prepared base so that front edges touch. Level block in both directions. Check individual units as installed and check units with each other as you install wall. Begin next course by laying a block with the rear lip down and pulling it forward until the lip is securely in contact with the units below. Assemble additional courses by placing units in a staggered relationship to the course beneath (running bond).

Fill behind each course with drainage aggregate (such as ¾-inch free draining) that extends 6 inches behind the wall. Compact aggregate with tamper. Organic soil or clay-type soil is not recommended for backfill material.

To make all blocks fit, you may need to cut wall blocks. Use a circular saw with a masonry blade to cut blocks and caps from the top. Read and understand the operating manual before using a saw.

90° Corner:

For some products, you will need to use a circular saw with a masonry blade. Cut a 45-degree angle on two blocks. Cut from the front corner to the back of the block. Glue pieces together with construction adhesive so two block faces form the finished outside corner.

For capping curves, trim caps to follow the wall radius. Place a cap at the beginning of the curve. Skip a space and place the next cap in the third position. Rest a cap on the top of the original two, aligning its face with the face of the wall. Mark the bottom of the cap along the edges. Use a circular saw with a masonry blade to cut the marked cap. Place the cap. On a 90-degree corner wall, the caps need to be saw-cut to achieve a 45-degree mitered corner. At the end of the wall, cut the cap so the manufactured edge is exposed and the cut edge is against the next cap.

Use an exterior concrete construction adhesive to secure the caps.