A retaining wall is a functional and fashionable way to create a level area on a slope for a flower garden or to prevent erosion on a sloped landscape. Building and installing one is a great do-it-yourself project that can turn a previously unused hill into a dynamic landscape space.
Why Build a Retaining Wall?
Retaining walls are a great way to create a more useful and beautiful landscape around your home. They hold back large amounts of soil that might otherwise slide down a slope during heavy rains or potentially, cause foundation or landscape damage. Retaining walls can be used to create a useable, level area for a small patio or lawn on properties, or they can create a terraced landscape area for plantings and gardens.
Note: Depending on the scale of the project, you may be able to make the cuts into a hillside and redistribute the soil by hand, or you may need a machine. If you're feeling adventurous, rent an easy-to-operate mini-backhoe/loader; otherwise, hire an excavator.
Step 1: Decide on Building Materials
Retaining walls can be made from a variety of materials, including wood blocks, bricks, natural stone and concrete. For the practical DIYer, interlocking mortarless blocks are the best option. These blocks have a lip on the backside so they connect easily without mortar.
Do not use mortarless blocks if you're building a wall more than 3' high. Higher walls need more reinforcement.
When the blocks are delivered, do not have the pallets set on a paved surface such as your driveway. They are extremely heavy and can cause damage to surfaces.
Step 2: Measure and Lay it Out
Determine the desired height and length of your retaining wall. Using a tape measure, find the length (the average is about 1' long) and the height of the mortarless block you plan on using. Divide the length of your proposed wall by the length of the block. This will determine the number of blocks you'll need for one row. Next, divide the height of the wall by the height of the block to determine the number of rows. To find out the total number of blocks required, multiply the number of blocks per row by the number of rows.
Step 3: Excavate
Mark the area where you want to put your wall using wood stakes and landscaping twine. Use landscaping spray paint to mark a line along the string on the ground. It's important to build your retaining wall on a level foundation. Clear the building site of debris, grass and any other material. Starting at the lowest point on the slope behind your staked-off line, use a flat-pointed shovel to dig a trench for the foundation row. The dimensions of the trench will vary depending on the size of your blocks, but plan on making the trench 4" to 6" deep and a little wider than the width of a block. Compact the trench soil, using a hand tamper, and then add a layer of leveling sand and tamp it down.
If you want a gently curving wall, lay down a garden hose or length of rope to guide your excavation instead of stakes and twine. Mark the shape with landscape paint.
Wear heavy work gloves and sturdy boots to protect your hands and feet from injury.
Always bend at the knees and use your legs, not your back, to lift blocks.
Before digging or excavating, be sure you know where underground utility lines are located in your yard. You can find out by contacting your local utility service providers.
Check to see whether or not you need a work permit from your local municipality to construct your retaining wall.
Step 4: Lay the Blocks
Set the first block in place. Use a level to make sure it's level on all sides. Tap it down with a rubber mallet to adjust, if necessary. Continue laying the first row of blocks in this way until this foundation row is completed. Then set the first two blocks of the next row on top of the foundation row. Position one at each end. The lip on each block should fit against the back of the foundation block. Remove the blocks for now and set them aside.
Step 5: Cut Blocks for the Next Row
You'll need to cut one block so the first and second row vertical joints are staggered. Do this also for each additional row added. To make the cut, use a 3½" brick chisel and a hand-drilling hammer (small sledge) to score a cut line all around the middle of one of the blocks. It takes a little patience, but when the scored line is deep enough on all sides, the block will break in half on the line. You can use this same process to adjust block size when and if needed.
Step 6: Finish Laying the Blocks
Stack the blocks for the second row on top of the first row, beginning with the half block. Step each course back a little as directed by the stone manufacturer. Typically, you will want the wall to slope backward (towards the slope) 1" for every 12" of height. This will help keep the wall in place, rather than toppling forward over time if the slope pushes against it with too much force. As you finish a row, lay a level across the top of the blocks to ensure that they are all level.
Step 7: Fill the Wall Cavity
To help prevent soil from gradually pushing through the spaces between the blocks, line the cavity behind the wall with landscaping fabric. Start at the base of the cavity and unroll the fabric until it overlaps the top row of blocks. Cut the fabric with garden shears and continue along the length of the wall until the entire cavity is lined. For drainage purposes, fill the area closest to the blocks with fine gravel before backfilling the rest of the cavity with soil. Trim excess fabric to fit. Fill the cavity with soil until it is just a few inches from the tops of the blocks, tamping it down occasionally so the soil is compacted. You should now have a level terrace behind the wall.
Step 8: Complete the Wall
Using a caulking gun, secure the top row of blocks with concrete bond adhesive. Firmly press on each block and allow the adhesive to dry according to the manufacturer's instructions. If you’re going to be planting a flower garden here, add a 2" layer of mulch on top of the topsoil.
That’s it! You’re done. You've got a strong defense against erosion and added to your landscape's overall appeal.
Project Shopping List
Here’s what you’ll need to complete this project successfully.