How to Build a Retaining Wall with Blocks

Build a retaining wall by excavating a level trench, laying a gravel base, and stacking interlocking blocks in offset rows while backfilling with gravel for drainage.

1. Call Before You Dig. Mark your wall location with spray paint or stakes and string. Check local codes for height restrictions and setback requirements. Call 811 to mark underground utilities before digging. Measure and calculate the number of blocks needed, adding 10% extra for cuts and mistakes.
2. Dig Deep and Level. Dig a trench 6 inches wider than your block width and 6 inches deep for every foot of wall height, with a minimum of 6 inches. For a 3-foot wall, dig 18 inches deep. Make the trench level using a 4-foot level and add or remove soil as needed. Compact the soil with a hand tamper.
3. Lay the Drainage Layer. Add 6 inches of crushed gravel to the trench and rake it level. Compact the gravel thoroughly with a plate compactor or hand tamper. Check for level across the entire base using a long level or transit. This base prevents settling and provides drainage.
4. Perfect First Row Wins. Place the first row of blocks on the gravel base, checking each block for level front to back and side to side. Use a rubber mallet to adjust blocks into position. Ensure the first course is perfectly level and straight, as it determines the entire wall's alignment. Check alignment with a string line.
5. Drainage Prevents Failure. Place 12 inches of clean gravel behind the first course before adding the second row. This drainage layer prevents water buildup that could damage your wall. Use 3/4-inch clean gravel, not sand or fine material that can clog.
6. Stack With Offset Pattern. Stack additional rows, offsetting each course by half a block length to create a running bond pattern. Most retaining wall blocks have an automatic setback built in. Check each course for level and use a dead blow hammer to seat blocks firmly. Install any required geogrid reinforcement according to manufacturer specifications.
7. Custom Cuts for Corners. Cut blocks to fit using a concrete saw with a diamond blade or a chisel and hammer for small adjustments. Always wear safety glasses and dust protection when cutting. Smooth rough edges with a grinder if necessary for a professional appearance.
8. Crown the Wall. Place cap blocks on the top course using concrete adhesive to prevent movement. These finishing blocks provide a clean appearance and help shed water. Ensure caps are level and properly aligned with the wall face.
9. Compact in Lifts. Fill behind the wall with more drainage gravel up to within 12 inches of the top, then add topsoil for the final layer. Compact backfill material in 8-inch lifts to prevent settling. Install drainage pipe at the base if required by local codes or for areas with heavy water flow.