How to Build an Interlocking Retaining Wall

Hammer two wood stakes into the ground, one at either end of where the retaining wall will be. Tie a string between the two stakes to indicate where the retaining wall's front edge will be.

Dig a 24-inch wide trench behind this rope. Make the trench between 4 to 6 inches deeper than the thickness of the interlocking retaining wall blocks you are using. Compact the trench with a hand tamper.

Pour crushed gravel into the trench. Level out the gravel into an even 4- to 6-inch deep layer with a metal rake. The depth of gravel depends on your climate. The colder your climate, the more crushed gravel you should use to help prevent frost from heaving the retaining wall.

Compact the crushed gravel with a hand tamper. Pour leveling sand into the trench and spread it out into an even, 1-inch layer. Compact the leveling sand with a hand tamper.

Use a hammer and a chisel to remove the lip on each of the retaining wall blocks to be used in the base layer. Lay these blocks on the leveling sand. Place a level over the blocks. Adjust the sand underneath the blocks so they sit flush in the trench. Place a torpedo level along each block and check how it sits in the trench from front to back. Hit the blocks' high ends with a rubber mallet to sink them into the leveling sand. Backfill behind the first layer of retaining wall blocks with crushed gravel.

Measure the width of a retaining wall block and divide it in half. Draw a chalk line over the block, dividing it in half. Lay the block on a guillotine cutter, line up the chalk line with the cutting blade, and tighten the handle to hold it in place. Pull the guillotine cutter's handle down to split the block in half.

Lay the cut block on one end of the retaining wall. Starting with a half block offsets the first layer's meeting joints from the second layer's meeting joints. Continue to lay full blocks over the first layer, making sure that the lips and grooves line up and hold each block in place.

Start the third layer with a full retaining wall block and stagger the third row's meeting joints from the second layer's meeting joints. Start the fourth layer with half a block to stagger the joints. Continue to build up your retaining wall until you reach your desired height. Keep in mind it is not recommended to build interlocking retaining walls higher than 4 feet tall.

Apply two parallel beads of retaining wall block adhesive over the surface of the top layer of blocks. Set a retaining wall cap over the blocks, in the adhesive. You can either line up the cap's front edge with the retaining wall blocks' front edges or pull it forward one inch. Install wall caps all the way down the retaining wall.