What You Need for This Project
Building Retaining Walls
Interlocking concrete retaining blocks require no mortar. Aside from the weight, they're almost as easy to assemble as children's interlocking bricks. If you make mistakes or change your mind about the location or shape of your wall as you're building, just dismantle it and start over.
Since these systems use no mortar or rebar reinforcement system, they're more appropriate for terraces or raised beds with low walls, instead of those with tall walls. A system of terraces creates a pleasant, stepped slope that's safer than a single, tall wall. It also gives you mant planting and landscaping opportunities and helps control erosion.
How to Build a Retaining Wall
Measure & Mark Off
Measure out your prospective wall using stakes and mason line (string) to mark off the key points. If you can't get your hands on stakes and string, you can use a garden hose to mark off the perimeter.
Dig a Trench
Dig a trench for the foundation course. The dimensions will vary depending on the size of your block, but it will generally be about 4 to 6 in. deep. The width of the trench should be twice the front-to-back measurement of your blocks. Remember, the foundation course should be partially below ground level.
Flatten the Trench
Tamp down the trench with your hand tamper to compact the underlying soil. If you find this too physically difficult or the vibrations are uncomfortable, you can drop the tamper from a height of about 9 in. and let gravity tamp down the soil for you.
Smooth out the Trench
Gently rake the trench so the soil isn't a hard compacted layer. Use the level to make sure you've got a level surfaced, and rake soil around to remove any dips or bumps.
Line the Trench with Landscape Fabric
To prevent soil from seeping through the spaces between the blocks, line the trench with porous landscape fabric. Start at the base of the trench and unroll the fabric to a length that will overlap where the top course of block will be. Cut the fabric and continue along the length of the wall until you've lined the entire trench.
Use staples to secure the landscape fabric into place so that when you move around the blocks to make final adjustments, the fabric will line the trench as originally planned.
Pour in Pea Gravel
Pour pea gravel over the landscape fabric until you have a layer a couple inches thick. This will help water to drain properly. Adding proper drainage prevents water pressure from building up behind the wall and causing it to collapse. All retaining walls encounter the force of water, whether it's from heavy rains or some other unforeseen event.
Use a level to periodically check that the layer of pea gravel is even. Tamp it down to make it firm, then use a rake to smooth out dips and bumps.
Chisel the Foundation Blocks
Use a chisel and hammer to remove the rear lip from the blocks you'll use for the foundation course.
Add the First Block
Set the first block in place and use the level to check that it's even. If the block isn't level, add a small amount of pea gravel as needed and tap the block with the rubber mallet or butt end of your hammer to adjust it.
Check That the Blocks are Level
If your property is relatively flat, continue laying the foundation course, making sure that all blocks are level and partially below ground. If your property isn't flat, use the stepped method mentioned above.
Levelling provides strength and prevents the wall from tipping forward. It's a key factor to a long-lasting wall. If you leave the wall uneven at the base, the error will grow exponentially with each course. It's much easier to make the correction early on than to try and correct it later.
Start the Second Course
Cut one block in half, length-wise, for the start of the second course. This ensures that the first and second courses are staggered in a brick-like pattern. Wear eye protection when cutting the block. If you're using a power saw, you'll also need hearing protection and a dust mask.
Set the rest of the second course blocks in place, finishing with the remaining half of the starter block you cut. Check that the row of blocks is level and correct any areas that aren't before adding additional courses.
Clean the Blocks
Make sure to periodically clean off each block so there's no dirt or gravel trapped in between the courses. If there is, you could inadvertently make the whole course uneven and off-balance.
Adhere the Caps
Once you're done with the courses, carefully sweep any dust or debris off the top of the blocks. Apply construction adhesive to the clean surface and secure the final course of blocks or wall caps to your wall.
Last Level Check
Use your level to do one final check that all courses are even. If not, use your mallet or hammer to gently nudge them into place until they are perfectly even.
Apply Mulch, Sod or Topsoil
Fold any excess landscape fabric over the gravel and cover with sod, topsoil, or mulch.
How To Terms
- Add the First Block
- Adhere the Caps
- Apply Mulch, Sod or Topsoil
- Check That the Blocks are Level
- Chisel the Foundation Blocks
- Clean the Blocks
- Dig a Trench
- Flatten the Trench
- Last Level Check
- Line the Trench with Landscape Fabric
- Measure & Mark Off
- Pour in Pea Gravel
- Smooth out the Trench
- Start the Second Course
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