How to Build a Block Retaining Wall

Retaining Wall
Stackable stone walls create a nice border and increase lawn or garden space. (DepositPhotos)

Retaining walls can be a great way not only to help with erosion and water drainage but also to create beautiful, usable garden space. And thanks to interlocking, stackable blocks, the project can be completed in a weekend.

Building a retaining wall is a tough job, but it’s something most homeowners can handle, as long as you’re able to do some heavy lifting and are willing to get dirty. Here’s what you need to know to build your own stackable retaining wall.


Stackable Concrete Blocks

Stackable stones are made of concrete, with a decorative finish on the front and a lip on the back. The lip fits snugly against the block below it, creating an interlocking joint that holds up to pressure, while the decorative front gives an attractive finish.

The stones are often slightly wedge-shaped to allow you to create gentle curves. With many styles, thin “topper” stones are also available, to give the wall a finished appearance.

Building Tip

Stackable stones are generally recommended for walls less than 3’- 4’ high. Taller walls typically need additional structural reinforcement and may require a building permit along with professional advice or help.


Materials Needed

For this project, you will need:

  • Work gloves
  • Shovel and/or mattock
  • Brick chisel and small sledgehammer
  • Level
  • Wooden stakes
  • String and a line level
  • Soil tamper
  • Gravel (sharp, not rounded) or rock dust
  • Landscape fabric (optional)
  • Interlocking stackable stones and toppers

Estimating the number of blocks you’ll need is tough. Count on at least one block per linear foot, and count on it taking more blocks than your estimate suggests!


Layout and Planning

  1. Before you begin, check with your city utilities office, or dial 811 to make sure there aren’t any buried pipes or cables in your digging zone.
  2. Use a garden hose to lay out a pleasing line for your retaining wall. Mark the ground using flour layout lines or landscape marking paint.

Digging the Trench

  1. Along your marked line, carefully dig a trench slightly wider than the blocks (ideally, the width of your soil tamper), and deep enough so the first course of blocks is below ground level. Cut straight down with the shovel keep from disturbing the surrounding soil.
  2. Make the trench as level as you can, to save time later.
  3. If your wall goes across a slope, you can dig a series of stepped trenches so that only one course of blocks is below ground.
  4. Tamp down the bottom of the trench using a soil tamper.
  5. Add several inches of sharp gravel or rock dust to the bottom of the trench, and use this layer to do your final leveling and tamping.

Laying the First Course

  1. Start at the edge of the wall that’s most visible, or the edge that butts up against another structure. If your wall goes across a slope, start at the lowest end.
  2. Position the first stone in your trench. Make sure the stone is level from front to back and side to side. Adjust by lifting the stone and adding more gravel or digging deeper as necessary.
  3. Hammer wooden stakes in the ground at each end of the trench, and stretch a string between them even with the top of the first stone. Level the string with a line level, and use the string as a guide for laying the rest of the first course.
  4. Continue laying stones side-by-side along your trench, making sure they are level. Getting the first course right is the key to a successful wall.

Laying Additional Courses

  1. Each row of blocks is offset from the one below it. If your wall has straight edges on the ends, start your next course with a block that has been cut in half.
  2. If you’ve worked hard to make sure everything is level, then this is the fun part. Continue laying courses of stones, making sure the lip of the stone is tight against the stone below it, and also making sure the seams are offset. The front edge will have a slightly “stepped-back” look due to the lips on the stones.
  3. Periodically check to make sure the stones are level and wobble-free.
  4. Build up the wall to the desired height, and top with topper stones if desired.

Building Tip

To cut a block in two, score a line around the middle with a brick chisel, then position the chisel on your scored line, and strike it with the small sledgehammer.


Backfilling

  1. To keep your wall clean, spread landscape fabric up against the wall before backfilling.
  2. Backfill the area behind the wall in layers, with gravel against the wall and fill dirt behind it, firmly tamping down each layer.
  3. Finish with a layer of topsoil.

Building Tip

If your wall is intended to divert water runoff, place a perforated drain pipe against the back of the wall before backfilling.


Further Information