Nov 25 , 2015

How To Build a Retaining Wall – Complete Step By Step Guide

Building a retaining wall is one of the best ways to transform your yard and increase your usable space. If you’re looking for landscape design ideas, then this is going to be a key part.

When I first wanted to learn how to build a retaining wall, I was annoyed the tutorials that were online at the time, so I decided to put something together that dominates them all.

I recommend you watch the video above, but if you prefer reading, I’ve summarized the steps below. However, the video does have more information.

Let’s jump right into it!

Step #1 – Plan And Design Your Retaining Wall

Retaining wall construction is a labor intensive process. It’s not something you’ll want to do twice. So, planning your wall design and layout is an important step. Not only will it help you achieve a better final result, it will help save you time and effort.

Here are some things to consider:

  • Surrounding features – The first thing you’ll want to consider is the surrounding features. Everything from trees to fire pits to sheds, you’ll want to consider them all. Since the hardscape is the first step in landscaping any yard, and it’s labor intensive to change, you’ll want to think 10 steps ahead. How do you plan on using the space?
  • Dirt Management – You might think that the majority of the work will be in moving blocks, but that’s far from the reality. Most of your time and effort will be spent moving dirt. So, think through where you’re going to put it during each step. Also, make sure to consider how much dirt you’ll need to achieve your design. Ideally, you will strategically move the dirt so you don’t need to get rid of any when your done, or truck any extra dirt in. In the video above, I used the dirt from the bottom of the hill to fill in the top of the wall once the wall was built. This saved time and money.
  • Wall height – Short walls require very little digging, can use small blocks, and don’t need any permits from the city. Large walls need larger blocks, more sophisticated designs, and a lot more digging. In most states, you can build a retaining wall up to 3′ tall without a permit. In the video above, I built a 3′ retaining wall.
  • Landscaping Blocks – There’s a wide assortment of retaining wall block designs to choose from. Once you know the height and layout you want for your wall, only then should you start shopping for blocks since the height will largely determine the blocks you can use. Again, taller walls require beefier blocks. I recommend going to a store that specializing in selling landscaping materials and consult with them. They’ll be able to point you toward the best blocks for your unique situation. A local company will also be familiar with the dirt in your area and special considerations you’ll need to take.
  • Grading – Anytime you are doing landscaping, you must considering the grading, or slope of the land. You never want to build a completely flat landscape because water will just puddle up and cause issues. So, take a look at your yard and see how it’s setup to drain right now. You’ll want to work with the existing draining, or completely modify it. But, either way, you must plan the grading around your retaining wall so the water drains off of your property. If you live in a suburban area, you also want to make sure the water isn’t draining into your neighbors yard. If you live in a rural area, you’ll want to pay attention to water rights.

Step #2 – Start Digging!

Now that you’ve planned your wall, it’s time to start digging a trench for the paver base and first layer of blocks. First, mark the location of your wall by either dragging a shovel in the dirt or with spray paint.

Dig your trench about twice as wide as the blocks you will be using and as deep as you need it to be to accommodate for the paver base and for the first block to be at least half-way buried. If you’re using 6″ tall blocks, you’ll want to dig about 9″ deeper than ground level. That will allow for 6″ of packed paver base and for half of the bottom block to be buried. Of course you can always dig deeper, but don’t cut corners and dig your trench too shallow.

Step #3 – Packed Gravel Base

If you want a straight wall that lasts a lifetime without shifting and moving, you’ll want to put down a layer of packed gravel base (or concrete) before adding your first row of blocks. This step is NOT optional. It’s essential.

If you’re building a short retaining wall, you might only need a couple of inches of base, or even none at all. And, if you’re building a wall taller than 3′, you might need even more than 6″. Follow your local block suppliers guidance on base depth for the system you are using. Typically 6″ of packed gravel base is recommended.

Add the gravel base in 2″ layers, and pack it down thoroughly after each layer. You can use a hand tamper or there are plenty of machines out there to assist you.

Step #4 – Level the Base

Take your time and level the gravel base well. You want it to be perfectly level. Never build your wall at an incline. If you are building your wall up a hill, then you’ll want to step it up instead of sloping the actual blocks. The blocks themselves must be level for structural purposes.

This is your only chance to level the wall. You won’t be able to fix the wall later once it’s built and your wall will only be as good as the layer of packed gravel base. So, take your time! Don’t let the idea slip into your mind that this should be fast or easy. This step takes time and attention, and even multiple passes to get it level.

To level it, you can either use stakes with a string and a line-level. Or, you can simply grab a 4′ level (or longer) and work your way down the trench adding or subtracting gravel as you go.

Make sure to pack the gravel down as you level it.

Step #5 – First Row Of Blocks

You’re finally ready to start laying the blocks! Congratulations!

Start at one end of the wall and install one block at a time, leveling side to side and front to back. Again, this first row is extremely important because you won’t be able to go back and fix it later. Getting lazy here will just cause more work later, make your wall weaker, and make your friends laugh when they see your crappy construction.

This is a time consuming part, but here’s a tip to make it easier. Grab a bag of sand (the kind used for leveling patio pavers) and a hand shovel and use the sand to make minor adjustments. This will make leveling the blocks go much faster since it’s so much easier to work with than the gravel.

“Set” each block with by hitting it in the center a few times with a rubber mallet once it’s been leveled.

Step #6 – Add Gravel Behind The First Row

Once you have the first row of blocks in place, and they are level and aligned with each other, the next step is to add some gravel for drainage behind the blocks. Shovel in some 3/4″ rough gravel behind the blocks. This is different than the gravel used for the packed base. You can ask your rock yard for recommendations on gravel to use for this.

Once you’ve added the gravel, add some dirt in front of the first row of blocks to hold them in place. Then, lightly pack down the gravel and the dirt around the blocks to lock them in place. Be careful not to pack too hard or you’ll move your blocks.

You’ll want about 6″ of gravel for drainage all the way up the wall. So, as you build the wall, you’ll probably need to add some dirt and some gravel as the wall gets taller. Be sure to tamp down the gravel and backfilled soil after each row of blocks!

If this sounds confusing, that’s why I made the video above!

Step #7 – Another Layer of Blocks

Now that you have the first layer in, this part is easy. Just add the blocks one by one making sure to overlap the seems. Make sure the blocks sit snugly on the other blocks. Sometimes rocks and dirt will get in between them and mess up your nice level wall. Don’t let that happen.

Repeat Steps #6 and #7 Until the Final Layer

Step #8 – Final Layer

You’ll want to glue down the final layer with cement adhesive. So, grab a caulking gun and some cement adhesive, and liberally apply it to the bottom of each block on the top layer as you add the top layer. This will prevent somebody from easily disassembling your hard earned wall.

You’re almost done!

Step #9 – Add Soil to Wall

For the final layer, you probably won’t want to see the drainage gravel. So, this time you’ll skip the gravel and just backfill the wall with top-soil. No need to pack this layer either, unless you want to.

And your done!

How To Cut Retaining Wall Blocks

There are two ways to cut retaining wall blocks.

Method #1 – Chisel and Hammer

Grab a masonry chisel and a mini sledge. Draw a straight line all the way around the block where you want to make your cut. Then, take your chisel and hammer and chisel a notch all the way around the block. Once you have a groove all the way around the block, place the chisel in the groove and hit it a bit harder with the hammer. The block should split pretty nicely.

Method #2 – Angle Grinder

If you have an angle grinder with a diamond blade on it, cutting the blocks will be even easier. Again, mark the block all the way around where you want to cut it. Then, grind a groove all the way around the block. Then, take a sledge and a chisel, place the chisel in the groove, and give it a tap. The block should split no problem.

Final Thoughts

Building a retaining wall is a lot of work – even more than you might think. The wall I built in the video took me over 6 months of slowly chipping at it to build it. It is a pretty big wall at 3′ tall and 50′ long. But, even a short wall will be a large project.

As a pro handyman, I would never take on a project like this for a customer without a crew to help me. It just wouldn’t be profitable and I’d have to break my back trying to stick to a timeline.

But, if you want to transform your own yard, and are willing to take your time, this is a very fulfilling project to take on. Enjoy!

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