How to Build an Interlocking Retaining Wall

Lay out the wall and remove the soil from the slope. Following the manufacturer's recommendations, dig and level a trench for the first course. Stake a mason's line to help align the blocks.

Starting a foot beyond the top edge of the slope, spread landscape fabric down and over the trench. Put stones on the top to hold the fabric in place. Overlap the fabric edges by 6 inches. Tamp 3 to 4 inches of gravel into the trench and back to the bottom of the excavation.

Using the line or the edge of the trench to guide you, lay the first course in the trench. The first course blocks are set backwards for many styles. Set each block with a rubber mallet. Make sure each block is level front to back and with the adjoining blocks. Use a 4-foot level to check—shorter levels are not long enough to ensure accuracy. If you need less than a full block at the end of the wall, lay smaller blocks or trim full blocks to fit.

Set the remaining courses with the flanges tight against the back of the preceding course. Start every other course with a half or partial block so the joints are offset by at least 3 inches or the amount specified by the manufacturer's instructions. As you work, check the blocks for level. Shim the low end of a block with a small piece of cedar shingle.

After the third course of block, backfill the area between the wall and the slope with gravel, just about even with the second course. Lay in a perforated plastic drainpipe on the gravel (holes down). Let the pipe daylight beyond the edge of the wall, or run it into a French drain.

As you build the wall, backfill gravel behind it at least every other course, covering the pipe and bringing the level of gravel up just below the top of the last course you laid.

Using the same techniques and starting every other row with a partial block, continue building the wall and backfilling it with gravel. When you're one or two courses below finished height, fold the landscape fabric over the gravel and tuck it behind the block.

Shovel about 2 inches of the topsoil you removed (not the subsoil at the base of the slope) on top of the landscape fabric. Tamp the soil lightly with a garden rake and replace the sod.

The capstones made for block of this or a similar shape cover the V-shaped gaps between blocks in the lower courses. Prepare the next-to-last course by applying a bead of construction adhesive on the surface of each block.

Following the manufacturer's instructions place the course of capstones on the wall.

If you're not building a patio or other structure below the wall, spread and tamp the topsoil you removed from the excavation. Fill in around the base of the wall and level the soil as far forward from the base as the landscape allows. Tamp the soil and replace the sod. Water the sod frequently until it is well established.