How to Build An Interlocking Block Retaining Wall

A step-by-step guide to building your own retaining wall. Building a retaining wall is hard work, wave your time, energy, and sanity by getting it right the first time. 

Image source: Redi-Rock International

Retaining walls protect landscapes from soil erosion, making them useful for homeowners with hilly yards.  But, a retaining wall is also an exciting way to improve the look of your yard. These attractive features can create more usable space in your yard and increase the curb appeal of your home.

In this guide, we’ll cover in step-by-step instructions on how you can build your own retaining wall with interlocking stone or concrete blocks.

Required Tools:

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Step 1: Digging a Foundation

A trench approximately 6 inches deep and 12 inches wide.
Image source: The Bean Blog via Flickr

The most important step in building a sturdy wall is starting with a level base.

  • To create a sturdy foundation for your wall, you want to dig a trench to set your first level of blocks in. First though, you’ll need to measure out the area you’ll be building your wall.
  • Use a tape measure to find the length and width of the area that your wall will fill and mark that area off using garden stakes and string, or another method like sprinkler flags.
  • Once you’ve marked off the area, you’re ready to get digging. Use a shovel to dig a trench about 4 to 6 inches deep. The width of your trench should be about twice the width of your base stones.
  • After digging your foundation, you want to compact the soil as well as you can to create a sturdy base. A vibrating plate compactor would be useful for this step, but with a little elbow grease, a hand tamper works just as well.

Step 2: Building a Strong Foundation

A dirt tamping tool compacts soil to form a level foundation

Next, you’re going to want to use a paver base to create a solid foundation to build on. This step will keep your wall safe from soil erosion to keep it standing sturdy and stable for years to come.

  • Paver base is a construction aggregate of crushed up rocks, similar to gravel. You want to choose a paver base made up of landscape rocks that are close to half an inch in size.
  • Fill the trench with an evenly distributed 2 to 3-inch layer of paver base. Use a landscaping rake or other method to make sure the stones are distributed evenly.
  • Using your tamp or plate compactor, evenly compact the stones to create a level foundation.

Step 3: Laying the First Blocks 

Carefully level the first layer of stones to create a stable starting point for your retaining wall.

Now that you have a sturdy foundation, it’s finally time to start laying the first course of blocks.

  • As you place the first block, use a level to make sure it sits evenly. If necessary, use an additional layer of paver base to reposition the block and a rubber mallet to tap it into place.
  • Continue laying blocks using your level to check that each block sits level.
  • After you finish laying this first level of stone blocks, fill the gap between the wall and landscape with gravel. Afterward, tamper the gravel to provide more stability to the wall and reinforce it against soil erosion.

Step 4: Adding Levels to The Retaining Wall

Once your first course of stones has been laid, you have an even platform to build your additional courses on. Now it’s time to find your rhythm and start placing the next interlocking layer of blocks.

  • Because we’re building a wall of interlocked blocks, you don’t need to use any adhesives to keep them together.
  • You want to stagger each level of blocks to create this interlocked effect. If you only have one size of blocks, then you can do so by cutting a block in half with a circular saw. Be sure to use a masonry blade to avoid damaging the saw and wear a mask and safety glasses while cutting the stone.
  • Before laying your next level of stones, use a broom or brush to remove any debris from the top of the previous level.
  • Start this level of stones with the half-block and continue laying the blocks the same way you did for the first level.  When you reach the end of the row, finish it off with the other half of the cut block.
  • After completing each row of stones, fill the space between the wall and landscape with tampered gravel. Don’t worry about how this looks for now; we’ll cover the gravel in the final stage.
  • When adding any more layers to the wall, be sure to keep them staggered, cutting a block for each even-numbered level if needed.
  • Brush off the blocks after each level to remove any debris before continuing.

Step 5: Putting a Cap on It/Finishing the Wall

Once you’ve placed as many layers of blocks as you want, it’s time to finish off the wall with a layer of block caps. While technically not needed, these block caps are what really tie together the look of your wall and enhance its aesthetic.

  • Brush off the previous run of stones to remove any debris.
  • Unlike the previous levels, you want to use a construction adhesive to secure the block caps to the top layer of the wall. Make sure that the blocks and caps are dried so that the adhesive sticks properly.
  • Place the caps so that they overhang the blocks of the wall by 1 to 1-1/2 inches.
  • Finally, cover up the gravel between the retaining wall and landscape with a layer of topsoil or sod to let your garden or lawn grow against the wall and create a more natural look.
  • Consider adding landscape fabric or a layer of mulch, which will help keep weeds from growing in the area as well.
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