How to Retain a Rock Wall

Place a long rope on the ground and adjust it into the planned shape of your wall. Any curves in the wall should be broad.

Dig a trench, using a trenching hoe and flat-tipped shovel, along the side of the rope. Make it as wide as the largest rocks are plus 4 inches and deep enough to bury the first course of rocks, plus 5 inches. Make the bottom of the trench flat and pound the end of a tamping tool over the bottom several times.

Fill the bottom 3 inches with 3/4-inch angular gravel and spread it with the hoe. Tamp the rocks down so they lock together to provide a strong base.

Cover the gravel with a 2-inch layer of bedding sand and spread it smoothly by dragging a flat board across it.

Drop a large, flat rock on the bedding sand at one end of the trench against the outside wall. Do not drag the rock on the sand or you’ll need to smooth it out again. Set a bubble level on top of the rock and hit it with the handle end of a hammer until the rock sits even.

Butt the next rock against the first so the space between the two is minimal. Set the bubble level over the two and hit the second rock with the hammer until they are level. Continue setting the first course to the end of the trench, adjusting them with the hammer and verifying they are level after placing each rock.

Place a rock at each end of the wall to begin the second course. Use a line level to check that the rocks are even. If they’re not, wedge a small flat rock beneath the lower one until they're even.

Set the second course with large and medium rocks and stagger the joints by altering the size you use. Position the second course so it sits 1/4 to 1/2 inches in toward the soil the wall will retain. Leaning the wall slightly uses gravity to stabilize the wall. Fill in any gaps with small rocks and check that it’s level as you go.

Backfill the space behind the second course with gravel so it’s about 6 inches wide. Fill in the remaining space behind the gravel with soil.

Continue setting each course of rocks, leveling them as you go and backfilling the space behind each course with gravel and soil until the wall is at the planned height.