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Retaining walls keep landscape soil from eroding, but they also make a beautiful landscaping feature. A well-placed retaining wall can create more usable space in your yard, especially when your yard is naturally sloped or hilly. Building a retaining wall is a straightforward project that offers many benefits and landscaping opportunities.
This guide will teach you how to build a retaining wall with concrete blocks. Since this project will be labor-intensive, recruit at least one other person to help you with the digging and heavy-lifting.
Things to Consider
Here are some things to know before you start buying material and building a retaining wall:
- Depending on the wall’s height and your location, you may need a building permit to install a retaining wall. Check your local building codes and restrictions, as well as your homeowner's association (HOA) restrictions.
- Choose a DIY-friendly building material. Retaining walls can be made from wood, bricks, natural stones or concrete blocks. For DIYers, it’s best to use concrete retaining wall blocks, which can be interlocking and are heavy enough to stay in place without cement or other adhesive. Interlocking blocks fit together and add extra security to the wall.
- When the soil behind a retaining wall gets wet, it exerts much more pressure and weight against the wall. To relieve some of this pressure, your retaining wall needs proper drainage. Plan to backfill the wall with well-draining gravel or sand and install a drainage pipe.
- When buying material, purchase 10 percent more than what you estimate you need. This will account for any estimate errors and provide extra material for cutting blocks and replacing blocks in the future.
- Plan to build your wall after a long period without rain, when the soil is dry.
Plan the Location
- Using a tape measure, decide the length and the width of your retaining wall.
- Mark off the area with garden stakes and a mason’s line or other string. Tie the string to the stakes at the desired height of the wall. Make sure the string is level.
- If your wall will be curved, use paint to mark the shape and location of the wall.
Safety Tip: Stay safe by wearing protective eyewear, boots and work clothes while you install your retaining wall.
Dig a Trench and Level the Ground
The success of your retaining wall depends on a level base. To create a solid foundation, dig a trench for the first course of your interlocking retaining wall blocks. Make sure the ground remains even throughout.
- Begin digging into the ground with a shovel.
- The trench should be deep enough to bury at least half the height of your first course of blocks as they sit on a 2- to 3-inch base of gravel. Depending on the size of your blocks, this depth will be about 4 to 6 inches.
- The trench should be twice as wide as a single block.
- Once you’ve dug the trench, compact it with a hand tamper or vibrating plate compactor.
- Place a standard level on a 2 x 4 in the trench to ensure that the bottom is smooth and level.
Tip: The trench should account for any slopes. You may have to create steps up or down to ensure the top of the retaining wall will be level. The wall should never run parallel to a slope.
Lay the Base
Due to soil erosion, your retaining wall should be built on a solid foundation made from gravel.
- Choose gravel that has stones sized between 1/2-inch and 3/4-inch.
- Fill the trench with a 2- to 3-inch layer of gravel.
- Use a rake to ensure the stones are evenly distributed.
- Tamp the base with your tamper to make sure it’s evenly compacted.
Lay the First Course of Blocks
It’s time to start laying the retaining blocks on the sturdy base you just created.
- Center the first course of blocks in the middle of the trench.
- Position your first block and use a standard level to make sure it’s even. If needed, reposition it using additional gravel and a rubber mallet to tap it into place.
- Continue laying your first course of blocks, while checking that every block is level. Lift low blocks with more gravel and tap down high blocks with the rubber mallet.
- After you finish the first course, fill the space between your retaining wall and landscape with gravel.
- Tamp the gravel to increase the wall’s stability and durability against soil erosion.
Tip: If your retaining blocks have flanges, use a hammer and masonry chisel to knock off the flanges on the first course blocks to ensure they sit level.
Cut End Blocks
The blocks should be staggered, so you’ll need to cut the end blocks of each even-numbered course in half. For example, the second and fourth courses should have half end blocks, while the first and third courses should have full end blocks.
- Use a straight edge to draw a guideline down the middle of the block.
- Some retaining wall blocks have V-shaped notches on the backside. These notches allow you to easily cleave the block in half using a hammer and chisel.
- You can also cut blocks in half using a circular saw with a masonry blade.
- Always wear eye and ear protection and a dust or respirator mask for this step.
Lay Additional Courses
By installing an even first course, you’ve successfully laid the groundwork for more courses. Here’s how you lay the next levels of interlocking wall blocks.
- Brush off the first course of blocks with a broom to remove any debris.
- Start the second course of blocks with one half of the end block you cut in the previous step.
- Lay the rest of the second course blocks, interlocking them if applicable, and finish the course with the other half of your cut block.
- Check for level as you go and adjust as needed.
- Retaining wall blocks typically do not need adhesive to lay each course.
- If you wish to lay more than two courses, you only need to cut a block in half for the even-numbered courses. Following this rule will ensure your blocks are properly staggered.
- Brush off the blocks to clear away debris before starting the next course.
Install Drain Pipe (Optional)
If you get heavy rains, install a drainage pipe behind the wall. It may be easiest to do this when you’ve only installed one or two courses.
- Use a perforated corrugated pipe. The pipe should extend behind the entire length of the wall and drain somewhere the water can exit the area.
- Cover the pipe with a drain sleeve to keep sediment from clogging the drain.
- Pour gravel behind the wall to completely cover the pipe.
- Resume laying courses as needed.
Backfill the Wall
Once you’ve laid all the courses of blocks, you can fill in the area behind the wall.
- Backfill the wall with gravel or sand. If you use sand, first cover the backside of the retaining wall with landscape fabric. This will keep the sand from seeping between the blocks.
- If you’re backfilling with gravel, you can pour the gravel after every course you lay. This will give the gravel time to settle.
- Shovel in the backfill material in small portions. Tamp it down as you go, ensuring there are no hollow areas and it settles completely.
- Backfill up until slightly below the height of the wall.
- Fill the remaining space with sod or topsoil for growing grass or other plants.
Put down a layer of capstone blocks to complete your retaining wall and enhance the overall aesthetic.
- Brush off the last layer of stones and clean off any debris.
- Using construction adhesive, secure your capstones and create the top layer of your retaining wall. The block caps should overhang the retaining blocks by 1 to 1 1/2 inches.
- Replace the topsoil and sod in front of the retaining wall as needed. Consider accentuating the wall with nearby bushes, climbing plants and succulents so that it looks like a natural extension of your garden.
Tip: If your retaining blocks and block caps aren’t dry, the adhesive glue won’t hold properly.
A retaining wall is a functional and attractive addition to your yard’s landscaping. Learning how to build a retaining wall yourself is a great way to save money on labor costs. Don't worry if you don’t own the tools needed to complete this project. Rent what you need to build a retaining wall from The Home Depot Tool Rental.