How to Build a Retaining Wall

Spring has sprung, and the weather is perfect for that much-needed outdoor landscaping project that you’ve been putting off all winter. You know the one — where the rain is eroding your landscaping, where the steep slope is such an eyesore you don’t look out your back windows, where your land is unusable backyard space, or where you need a more beautifully tiered, front landscape to greet your guests. 

You need a retaining wall. Whether it is for managing water drainage or beautifying your landscaping, retaining walls serve many purposes. A great retaining wall can transform steep slopes into usable outdoor spaces and keep water from eroding your soil and get drainage to run away from your home, not towards it.

Here’s How to Start Building Your Retaining Wall

With the right materials, it is pretty easy for you to build your own retaining wall. One of the easiest ways a DIYer can do this is by using concrete retaining wall blocks that are interlocking and heavy enough to stay in place without cement or other adhesives. One of the most difficult ways is to forge material from a neutron star and haul it back to your home.

Soil is really heavy, especially when wet, so you need a heavy material to hold the soil in place. These kinds of concrete blocks hold back the soil with their weight, and they are shaped with a lip on the back of each block which creates a sloped, uniform, and easy-to-use setback when you stack the blocks.

You also need to calculate how high your wall needs to be. If you realize that your wall needs to be higher than four feet, you might rethink building this thing yourself, unless, of course, you are an engineer, or really tall. Consider that a basic retaining wall (4 feet tall x 15 feet long) has to support up to 20 tons of soil pressure — this thing has to be built solid to hold its shape and not give in under pressure.

If you are ready to do this, draw out a plan, and call 811 to have someone come out and mark your buried lines. There is going to be digging involved, and no one needs a gas leak. You also need to make sure that your area does not require a permit or that an HOA has requirements for your neighborhood.

When You Start Building, Here’s What You Do

Go ahead and get your materials. Quick reminder, look for concrete retaining wall blocks that have a lip on the back to make them interlock with each other. Because you are using retaining wall blocks, you will need to cut some of them to form straight lines with a brick joint pattern. The tool you will need is a block saw. With Northside Tool Rental, you can rent a block saw daily or weekly! And if you don’t know how to use it, they’ll help you get it figured out. Remember to always wear safety gear when working with this type of high-powered machinery. All in all, once you get used to it, you’re really just cutting straight lines — the machine makes it pretty easy to get a nice clean look.

Next, you need to measure and decide the length and width of your retaining wall, then mark off the area — if you have straight lines, then you can use garden stakes and string (or mason’s line). If your wall will be curved, you can use spray paint to mark the shape and location of the wall.

The Most Important Step in Building Your Retaining Wall

Once you know where your first rocks need to be placed, you need to dig a foundation. Here is the most important thing you need to know about building a retaining wall: Your retaining wall will only be as strong as its foundation — its support system. The following steps need to be followed to a T:

  • Dig the trench to be an eighth of the wall plus an extra three inches. Those extra three inches are there to spread crushed rock in the very bottom to keep the wall from shifting and settling. This also means that your first set of rocks will actually start in the ground. If you prefer to get a ditch dug really quickly without breaking your back, Northside Tool Rental has equipment available to get the digging done in at least half the time it would take to dig it by hand.
  • Once you’ve dug the trench, pour in the crushed rock. Choose a crushed rock 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 make sure the stones are level. In fact, you might want to rent a transit level to make sure that your base is level and then use it again once you have your first layer of rocks down to make sure your base rocks are completely level.
  • Tamp the base with your tamper to make sure it’s evenly compacted–compact it with a hand tamper or vibrating plate compactor.
  • Make sure your first row is level. Use either a transit level or use a four-foot carpenter’s level to get that first course of blocks level. Anything slightly off here will show up higher in the wall. 

Finishing Your Wall

Now is the time to start stacking your stones. Because your pattern will leave some end blocks uneven with the edge, you will need an electric block saw with a masonry blade to cut stones in half to have nice even edges. Make sure to wear eye and ear protection and a mask for dust whenever you cut the blocks.

One of the engineering functions you need to think through when building your retaining wall is how the water will drain through, under, or around the wall so that it doesn’t put added pressure on the backside of the wall (nobody wants added pressure on their backside). You will need to install a flexible perforated drain pipe while backfilling the space behind the wall with crushed stone.

Put the drainage pipe at the base of the wall, and cover the pipe with a drain sleeve to keep anything from clogging the drain. The perforated pipe will allow the groundwater to move to each base end of the wall, to avoid building up pressure behind your wall. Once the drainpipe is in place, backfill the rest of the space behind the blocks with either sand or pea gravel. Both allow water to filter through to the drainpipe.

The best way to backfill the retaining wall is to do a few inches after laying each round of blocks. Once you have put another layer of blocks down, pour some pea gravel, and then tamp the backfill every 6 inches, making sure it is packed tightly. Another quick tip: brush off the tops of each layer of block after you lay them down and before you begin another layer — the key here is to keep your wall as level as possible all the way to the top. 

When you need the advice and the right tools to create the professional-looking landscapes you’ve been looking for, Northside Tool Rental has it all. Contact us today for more information about renting tools to get working on terracing that eye-sore into a beautifully landscaped focal point!