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- Total Time: 1 day, 6 hours
- Skill Level: Advanced
- Estimated Cost: $20 to $35 per sq. ft.
- Yield: Concrete block retaining wall
A concrete block retaining wall provides the muscle you need to keep soil from sliding into your garden or other areas of your outdoor living space—you might want to add one after digging into a slope for a pathway, patio, or landscaping project.
The retaining wall provides a way to release the water that builds up in the slope behind it. Without a pressure-relief system, the weight of the water in the soil would crack or even buckle the wall. Concrete block retaining walls are similar to freestanding block walls but with a few crucial differences—for one, they’re stronger.
Getting Started
Sure, they’re functional, but you can also think of them as a landscaping feature that defines an area or separates areas of your yard. Before you get started, design the layout, and check with authorities on any local codes on retaining walls and any permits you might need. Expect to spend 20 to 36 hours building a 3×10-foot concrete block retaining wall.
What You’ll Need
Equipment / Tools
- Measuring tape
- Brick set
- Small sledgehammer
- Chalkline
- Pencil
- Mason’s trowel
- Level
- Mason’s blocks
- Wheelbarrow
- Striking tool
- Story pole
- Shovel
Materials
- Concrete blocks
- 2×4 stakes
- 2×8 lumber
- Mortar
- Gravel
- 4-inch perforated drainpipe
- Landscape fabric
- ¾-inch pipe
Instructions
How to Build a Concrete Block Retaining Wall
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Build and Prep Footing
Lay out the wall and excavate the slope and the footing trench. Build the footing and insert rebar into the wet concrete at intervals corresponding to the cores in the blocks. Prepare the footing, spread mortar, and build leads, sliding the block over the rebar as needed.
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Insert Weep Holes
As you lay the second course of the concrete block retaining wall, insert weep holes (¾-inch pipe) into the mortar every third block. Chip off a small recess in the block and trowel a mortar bed for the pipe, sloping it slightly toward the front. Then, chip out a recess on the next block, butter the ears, and set the block.
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Scrape Off Excess Mortar
Stop occasionally to check the mortar. When it begins to set up slightly, scrape off the excess with an upswing of the edge of the trowel. Do not plug the weep holes with excess mortar as you remove it.
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Lay Landscape Fabric
After you’ve laid at least two courses, spread landscape fabric on the soil behind the base of the concrete block retaining wall, temporarily laying the excess over the grass on the slope. Lay rocks on the fabric to hold it while you work. Backfill the wall with gravel between the rear of the wall and the slope, laying perforated drainpipe on the gravel bed level with the top of the first course. Face the holes down.
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Cover Drainpipe
Shovel more gravel on top of the drainpipe. Backfill with additional gravel as you add courses to the wall. Fold the landscape fabric over the top of the gravel fill, and backfill with soil. Replace the sod.
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Fill with Mortar
When you reach the finished height of the concrete-block retaining wall, fill those cores containing rebar to the top with mortar. Mix the fill mortar slightly wetter than what you’d use for joints. Smooth the top with a trowel. Spread additional mortar, and lay cap block to finish the wall.
