Retaining walls allow you to manipulate the land, sculpting steep slopes into sections of level ground that increase the visual appeal of your yard. Stone and brick are common retaining walls materials, but concrete retaining wall blocks offer strength and durability at a fraction of the cost. These specially designed blocks have a lip on them to add stability. You can choose from several concrete colors, shapes and textures, including options that bear a striking resemblance to natural stone.
Building Concrete Block Retaining Walls
Lay out a garden hose to create the outline for curved walls, then transfer this design to the ground with landscaping spray paint. Drive stakes into the ground and attach string to each stake to lay out the design for straight retaining walls.
Dig a trench 5 to 7 inches deep, plus half the height of one concrete block. The depth allows room for a 4- to 6-inch gravel base layer, 1 inch for a smooth sand layer and enough space to bury half the blocks for the first course to ensure a well-anchored retaining wall. Sandy soils with good drainage only need a 4-inch base layer, while poorly draining clay soils benefit from a 6-inch base.
Fill the trench with a 4- to 6-inch layer of 3/4-inch minus gravel with sharp edges. Angular gravel with a mixture of gravel pieces and gravel dust compacts better than rounded gravel of a single size.
Spread the gravel into an even, level layer and pack the gravel tightly with a hand tamper. Depending on the size of the trench, you might be able to use a plate compactor to pack the gravel. Compacting the gravel makes it less likely to shift.
Pour 1 inch of coarse masonry sand over the gravel and spread it out evenly over the gravel base. Check the sand with a level and adjust it until the sand base is level.
Lay the first line concrete blocks directly on top of the sand and tap each block into place with a rubber mallet. Check the blocks for level as you lay the course. Add or remove sand, as needed, to adjust the blocks so they are level.
Pour gravel behind the blocks after laying the first course; the gravel acts as backfill to improve drainage so erosion doesn't push the blocks out of place. Backfill each course of blocks before continuing with the next course.
Lay drain tile -- black, perforated drainage pipe -- behind the wall and on top of the first backfill layer. Although drain tile is not required, it helps to direct water away from the block retaining wall.
Lay the second course of concrete blocks, setting the blocks 1/2 to 1 inch farther back than the first course, using the lip as a guide. This makes it less likely for the wall to shift. Apply a bead of construction adhesive to the bottom of the blocks to help secure the blocks to the previous course. Stagger the joints for a sturdier wall -- if you began the first course with a full block, then the second course should begin with a half block. To cut a block in half, score the block with a brick chisel and 3-pound sledgehammer, then tap with a hammer to split the block in two pieces. Backfill after the second course and continue laying additional courses until the wall reaches the desired height. Limit the wall height to about 3 feet tall. Use a professional for taller walls.
Place a course of capstone blocks on the top course of concrete blocks. The capstones conceal any holes or gaps between the blocks to give the wall a finished look.
Ideas for Concrete Block Retaining Walls
Use a concrete block retaining wall to create a raised flower bed against a small slope in your yard.
Build a concrete block retaining wall to prevent soil from eroding onto a leveled patio area. If you excavated your yard to build a level patio, there is likely a slope along at least one side of the patio that can slowly erode when it rains.
Turn a steep, inaccessible slope into several flat growing spaces with a series of short concrete block retaining walls. After terracing the slope, you can use the terraces as flower beds, install a water feature or, depending on the size of the terrace, to create an elevated patio. Building several short retaining walls is safer than installing a single, tall retaining wall because the soil pressure on the back of the walls is split among the separate walls.
Install a curved retaining wall to create flow in an outdoor space filled with straight lines, such as a boxy house and a yard filled with several rectangular planting spaces.
Cut steps into a hillside to provide easy access to different levels, then install concrete block retaining walls to prevent erosion on each side of the new stairs.
Line a walkway with a concrete block retaining wall to further help guide traffic and keep plants from expanding into the walkway. If the walkway goes downhill, you can create steps in the wall to follow this flow. For example, you might install four courses of block for the first 10 feet at the top of the hill, then step down to three courses of block for the next 10 feet, eventually working your way down to one course or no wall at the base of the hill.
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Things You Will Need
- Garden hose
- Spray paint
- Measuring tape
- Wooden stakes
- Mason's line
- Digging tools
- 3/4 minus gravel
- Hand tamper
- Masonry sand
- Rubber mallet
- Drain tile
- Construction adhesive
- Brick chisel
- 3-pound sledgehammer
- Consider hiring a professional contractor for retaining walls greater than 4 feet tall. Many areas require a building permit for walls over 4 feet, measured from the bottom of the footing to the top of the wall, and when the backslope is 2 feet horizontal to 1 foot vertical or greater.