How to Build a Concrete Retaining Wall

Add style and support to your yard with a concrete retaining wall. You can build one in just six steps.

container gardens in aluminum planters
Photo: Rob Cardillo 
Project Overview
  • Total Time: 1 day, 6 hours
  • Skill Level: Advanced

Concrete blocks are ideal for building walls to hold back the soil after you dig into a slope for a pathway, patio, or another landscaping project. Block retaining walls are generally the same as freestanding block walls but with a few important differences.

A retaining wall must provide 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. Weep holes, which are lengths of ¾-inch pipe inserted along the top of the first course, escort some of the water out. The other part of the system is a plastic drainpipe covered with gravel. As water accumulates behind the wall, it percolates through the gravel into the drainpipe, which carries it off safely.

Retaining walls must be stronger than freestanding walls. Insert rebar in the footing when you pour it; this should be done at every three blocks or at intervals specified by your local codes. As the last step, fill the cores around the rebar with mortar from the bottom to top.

Expect to spend 20-36 hours building a 3x10-foot concrete-block retaining wall. Before you begin, you'll need to design the layout and pour the footing.

What You'll Need

Equipment / Tools

  • 1 Measuring tape
  • 1 Brick set
  • 1 Small sledgehammer
  • 1 Chalkline
  • 1 Pencil
  • 1 Mason's trowel
  • 1 Level
  • 1 Mason's blocks
  • 1 Wheelbarrow
  • 1 Striking tool
  • 1 Story pole
  • 1 Shovel

Materials

  • 1 Concrete blocks
  • 1 2x4 stakes
  • 1 2x8 lumber
  • 1 Mortar
  • 1 Gravel
  • 1 4-inch perforated drainpipe
  • 1 Landscape fabric
  • 1 3/4-inch pipe

Instructions

  1. Build and Prep Footing

    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.

  2. Insert Weep Holes

    Insert Weep Holes

    As you lay the second course of block, 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.

  3. Scrape Off Excess Mortar

    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.

  4. Lay Landscape Fabric

    Lay Landscape Fabric

    After you've laid at least two courses, spread landscape fabric on the soil behind the base of the wall, temporarily laying the excess over the grass on the slope. Lay rocks on the fabric to hold it while you work. Between the rear of the wall and the slope, backfill the wall with gravel, laying perforated drainpipe on the gravel bed level with the top of the first course. Face the holes down.

  5. Cover Drainpipe

    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.

  6. Fill with Mortar

    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.

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