How to Build a Retaining Wall That Lasts

Determine exactly where your retaining wall will go by using a tape measure to plan out the length and width of your structure. Mark the final location by placing wooden stakes in the ground and tying a string line at the desired height of the wall. Make sure this line is level.

If your retaining wall is curved, use spray paint to mark the location instead.

The sturdiness of your retaining wall depends on how compact and level the base is. To construct the base, start by digging out a trench with a shovel where you previously marked the location. You will want the trench to be twice as wide as your concrete blocks and about 4 to 6 inches deep.

To check that the ground is level, you can temporarily place a two-by-four piece of lumber in the trench and set a standard level on top. Even if your ground has a pronounced slope, your trench still needs to be level so that your retaining wall blocks are level. In this case, dig a trench with steps up or down as needed.

Once your trench is cleared and level, compact the surface with a hand tamper.

Next, add gravel into your trench to complete the base. Choose gravel with stones from 1/2 to 3/4 inches in size and place a 2- to 3-inch layer. Spread the stone with a garden rake and ensure every section receives an even amount. Tamp down the gravel with a hand tamper.

Now that your retaining wall has a sturdy base to rest on, you can begin laying the first course of concrete blocks. Start at one end of your trench and lay the first block centered in the middle of the trench. Use a standard level to ensure the block is level before continuing. If needed, use a rubber mallet to lightly tap down on the block or add more gravel beneath to achieve levelness.

Lay the remaining first course of concrete blocks, checking the level of each one as you go. The levelness of this first row determines the levelness of your entire wall, so this step is crucial.

Once the entire first course of blocks is set, fill in the gap between your retaining wall and the soil behind it with gravel. Lightly tamp the gravel to increase the stability and decrease the soil erosion potential behind your wall.

Your next course of blocks should be staggered from the first course. To do this, you will need to cut one of your concrete blocks in half and place a half-block at each end of the retaining wall. In other words, cover the joints between the blocks on the first course with a full block on the second.

To cut a concrete block in half, use a tape measure and a straight edge to draw a guideline down the middle of the block. Then, cut along the line using a circular saw with a masonry blade. Be sure to wear eye protection, ear plugs, and a dust or respirator mask.

In some cases, you may want to install a drainage system at this point in the project. For example, if your yard is prone to heavy rain or has slopes that create pools of water, a drainage system behind your retaining wall could prevent future damage to the structure caused by this water. There are two main drainage methods to choose from: a drainage pipe or drainage fabric.

For the drainage pipe method, purchase a perforated corrugated pipe that extends the length of your retaining wall. Cover the pipe with a drain sleeve to keep it from getting clogged with dirt and debris, and install it behind your retaining wall. Place gravel around the pipe until it is completely covered. Water collected behind your retaining wall will enter the drainage pipe and drain away rather than collect.

For the drainage fabric method, purchase enough rolls of landscape fabric to cover the entire back surface of your retaining wall. Lay the entire section of drainage fabric down behind the wall. As you continue to build your retaining wall, guide the fabric up the wall, placing gravel behind it after each course.

Continue laying concrete block courses, staggering each layer. Between courses, be sure to keep the surface clean so each block makes a solid connection with the block beneath it. Routinely check the level of the wall as you go. Place the gravel behind each course to ensure it has time to pack down and settle.

While not entirely necessary, you can use a concrete adhesive between the last two rows of your concrete blocks for added stability—useful if your retaining wall is on the tall side. Add a couple of lines of concrete adhesive with a caulk gun to the block surface before installing the next course.

You can add capstone blocks to the top surface to give your retaining wall a finished look. Apply two lines of concrete adhesive with a caulk gun across the top surface of the last course of blocks. Secure your capstones on top, overhanging 1 to 1 ½ inches off the front.

Brush off the last layer of blocks and clean up any debris. Ensure a solid layer of gravel is installed behind your retaining wall. Fill in any exposed areas with topsoil and sod to complete the installation. You might also consider adding other finishing touches, like mulch or landscaping elements.