How to Lay Retaining Wall Blocks
A retaining-block wall adds another level to your landscape for planting, a patio or to level soil to remove a slope. A properly installed retaining-block wall will last a long time without heaving, weeds growing through the blocks or water collecting behind the blocks that can push the bottom of the wall out. Stackable retaining-wall blocks are easy to use with excellent results.
Lay out a straight, formal retaining wall by inserting a stake in the beginning and ending locations. Tie a string close to the ground between the stakes. For a curving wall, place garden hoses in position along the planned wall front. Spray over the string or garden hoses with landscaping paint to create the outline of the retaining-block wall.
Dig about 6 inches down in the soil about 2 feet wider than the retaining wall blocks are deep. Start from the lowest end of the grade and place a level every few feet to keep the trench level. If necessary, add soil to step up the thickness of a block or remove soil to step down the thickness of a block as needed to compensate for a steeper grade. The grade will be refined when installing the first row of blocks. Use a plate compactor and compact the soil in the base of the trench.
Pour 2 inches of gravel in the trench. Use a plate compactor and compact the gravel.
Start installing retaining-wall blocks from the end that meets a building or other structure. If the retaining wall does not intersect with a structure, start installing blocks from the lowest end.
Place a level on each block to ensure that the block is level front-to-back and side-to-side as well as aligned with the blocks on each side. Add gravel to raise blocks and tap the block with a lump hammer to compact the gravel beneath the block. Remove gravel if needed to lower blocks but try to tap into the gravel with the lump hammer first.
Install blocks stepped up or down as needed to keep one row of blocks below the soil level. Use a hand shovel to refine the steps created while digging and tamping in Step 2. If adding soil to step up a level, use the lump hammer to tamp the block to be sure the soil under the block is firmly compacted. Take your time and pay attention to detail with the first course so the rest of the wall will go in level.
Continue to lay subsequent courses of retaining-wall blocks offset from the course below. Position the center of each block over the seams of the blocks in the course below. Offset the front of the blocks 1/4 to 1/2 inch behind the front edge of the course below to add stability to the wall.
Place landscaping fabric down the back of the wall to prevent weeds from growing in the wall between the blocks. Secure the top of the landscaping fabric with capstones that finish off the top of the retaining-wall blocks.
Pour 2 inches of gravel behind the wall. Compact the gravel with a plate compactor.
Place perforated drainage pipe 2 to 4 inches from the back of the wall. The end of the pipe will need to drain freely, so be sure to use enough to reach an area where the end of the pipe can drain. Cover with gravel and add 2 inches of gravel above the drainage pipe. Cover the top of the gravel with landscaping fabric.
Replace soil to cover the landscaping fabric and add grass seed or landscaping plants.
Things You Will Need
- String and stakes, or garden hose
- Landscaping paint
- Tape measure
- Plate compactor
- Retaining-wall blocks
- Lump hammer
- Hand shovel
- Mason's chisel
- Landscaping fabric
- Cap stones
- Perforated drainage pipe
- Plate compactors can be rented from a contractor rental supply company.
- Cut blocks for offsetting rows by scoring with a mason's chisel on both sides. Place the block on sand or soft soil, position the mason's chisel along the score, and strike the mason's chisel with a lump hammer.
- Wear safety glasses when cutting blocks.