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Building an interlocking retaining wall

An interlocking retaining wall is an ideal way to add greater stability, create level areas, and inject visual interest to a sloped garden. Learn more about them and how to build one in this post.

What is an interlocking retaining wall?

An interlocking retaining wall is a specially designed structure made up of individual blocks that fit together like puzzle pieces.

They often have an interlocking mechanism that allows the blocks to lock into place, resulting in a sturdy and stable wall.

Stone retaining walls are a popular option, while some homeowners choose interlocking concrete blocks for garden retaining walls in a contemporary garden, and others prefer interlocking retaining walls of timber construction for a more rustic look.

interlocking retaining wall made of concrete

Why choose an interlocking retaining wall?

Here are some of the reasons that an interlocking retaining wall is an ideal choice if you need structural support and stability in an area with uneven ground:

  • Stability

A sloped garden can be prone to mudslides and heavy water runoff; a particular problem if your garden slopes towards your home.

Interlocking retaining walls provide greater stability, preventing erosion and ensuring the soil behind them remains in place even after heavy rainfall.

  • Easy installation

Without the need for mortar or specialised tools, building an interlocking retaining wall is a relatively straightforward process.

This makes it a manageable DIY project or a quick job for an experienced tradesperson.

  • Multiple design options

Interlocking wall blocks create level terraces or raised beds in sloped areas, adding visual appeal to your garden.

They also come in a variety of materials, shapes, sizes, and colours, providing a broad choice of options to complement your existing landscape.

Retaining wall made of timber

And when not to choose an interlocking retaining wall…

There are some instances when interlocking retaining walls are not appropriate:

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How to build an interlocking stone wall

An interlocking stone wall adds a timeless and charming feel to an outdoor space.

The irregular shapes and texture of stone creates a rustic look that blends harmoniously with the natural environment.

Want to build an interlocking stone wall in your garden? Here’s how:

Materials

  • Interlocking stone blocks (type and quantity suitable for your wall’s dimensions and aesthetic)
  • Landscaping fabric (to prevent weed growth)
  • Gravel (for levelling and drainage)
  • Drainpipe
  • Construction adhesive
  • Backfill material (e.g. gravel or soil)
  • Stakes and string

Tools

  • Stanley knife
  • Measuring tape
  • Shovel
  • Tamper or compactor (for packing and levelling)
  • 4ft level
  • Circular saw
  • Small sledgehammer or masonry hammer
  • Rubber mallet
  • Torpedo level (to help check your levels in tight spaces)
  • Bolster chisel
  • Caulk gun
  • Wheelbarrow
  • Safety gloves and goggles

Building an interlocking retaining wall: step-by-step

Before you begin construction, it’s recommended to check with your local planning authority, especially if you live in a conservation area.

Step 1: Plan and prepare

  • Mark the area for your wall using stakes and string (this will help to align the blocks) and make sure your outline aligns with the desired slope and contours of your garden
  • Dig out a trenched area within the boundaries you’ve created. and ensure it’s slightly wider than the width of your wall

Step 2: Prepare the base

  • Lay your landscape fabric over the base of the dug out area and up the vertical edge to help prevent weed growth, and overlap the fabric edges by about 6 inches
  • Add 3-4 inches of gravel to the dug out area to provide stability and proper drainage
  • Rake over and check the surface level with your spirit level

Step 3: Lay the first course

  • At the lowest point of your wall, lay the first course of interlocking stone blocks, using the edge of the trench to guide you
  • Check the level of the blocks from side-to-side and back-to-back
  • Tap the blocks into place firmly using a rubber mallet, checking the level periodically

Step 4: Build subsequent courses

  • Set the remaining courses with the flanges tight against the back of the preceding course
  • Stagger the joints between the blocks in each course by about 3 inches to enhance the structural integrity of the wall

Step 5: Insert drainage

  • After setting the third course, apply a layer of backfill material between the wall the slope so it’s even with the level of the second course
  • Lay in a perforated plastic drainpipe on the gravel (holes down) ensuring the end of the pipe can see daylight

Step 6: Backfill the wall

  • Set the remaining courses and backfill every other course, covering the drainpipe, bringing the level up to just below the top of the last course you laid

Step 7: Cut and fit blocks

  • Where needed, use your chisel and masonry hammer to cut blocks to specific shapes or sizes
  • Make sure each cut block fits securely into the wall with proper alignment
  • Remember to check your levels as you go

Step 8: Tuck the fabric

  • At this stage, you’re just one or two courses below the finished height of your wall and have backfilled to just below the last course you laid
  • Now, fold the landscape fabric over the backfill material and tuck it behind the block

Step 9: Turf

  • Shovel 2 inches of topsoil on top of the landscape fabric you’ve folded over and tamper lightly
  • Turf over the topsoil

Step 10: The finishing touch

  • Apply a layer of construction adhesive on the surface of the top course of blocks
  • Place the capstones on top of the adhesive to complete the structure
  • Level and tamper the ground around the base of the wall to even out the area

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