How to Build a Block Retaining Wall




Introduction: How to Build a Block Retaining Wall

I had an area on the side of my house that was a narrow path of flagstones and sloped down toward my neighbor's house. The space was pretty much unusable for anything except walking by. I decided to build a retaining wall on the property line, and raise up the ground to be level so I could reclaim this part of my yard and improve the look of my property. It's important to note that I've never built any type of wall before so this was my first attempt and I'm really pleased with the results.

This project used about 165 blocks, 30 bags of gravel, and my finished wall was 39 feet long. The total cost came in around $1,200. It took me around 80-90 hours to build from start to finish.

Step 1: Tools and Supplies

Step 2: Getting Started

A word of caution before we get started: The vast majority of time spent working on this wall was measuring, re-measuring, leveling, and measuring again. Stacking all the blocks once everything was measured took about 1 hour.

Your very first steps should be to decide where you want your wall, and place stakes accordingly. Run your mason line tightly between your stakes and hook your string level to it to be sure it's level. Double check this, because you aren't going to want to redo this part later on. Measure your block front to back. Then dig a trench about 3 inches bigger than that. You will need to make sure you have room for gravel in front and behind your blocks to allow water to drain. Dig your trench deep enough to allow you to put 1-2 inches of gravel while still leaving your first row of blocks partially buried. My blocks were 4 inches high. I dug a trench 4 inches deep and filled it with 2 inches of gravel. Then I packed the gravel down using a hand tamper. This left my block 2 inches below the ground. You can see from the photo that I also have gravel in front and behind the block.

Step 3: Prepare Your Block

The blocks I used were interlocking. They had a lip on the back that is meant to grab the back of the block below it and keep it from sliding forward. This gives the wall strength and allows it to resist being pushed over by the weight of all the dirt behind it. The bottom row of blocks is much easier to level and move around if this lip is removed. Use your pick to chip off the lip for each block that will be resting on the gravel.

Step 4: Level Your Block

Once you've laid your first block onto the packed gravel, lay your torpedo level on top of the block. It won't be level. Add and remove gravel from under your block until you are level. If you're off by just a tiny bit, try banging the top of the block with a rubber mallet. The first block I leveled took me about 10 minutes. After the first few it got a little quicker. Double check to be sure your block is perfectly in line with the string. In the third photo you can see the string lined up with the back of each block. I later changed my method to lining it up with the front of each block because the wall looked straighter that way.

Step 5: Add Blocks

Most of the time building your wall will be spent on this step. Place the next block (with lip removed) down alongside the one you just leveled. Use your torpedo level on the edges of the two blocks to determine whether your new block is too high or too low in relation to your nicely leveled block. Add or remove gravel until the two joining edges are at the same height. (Photo 1) Then place your level on the center of the block and add or remove gravel until it is level. Check the edges of the 2 blocks again to make sure they are still even with each other. If they are, congratulations! Go back to the beginning of this step and repeat until your wall is as long as you'd like it to be.

Step 6: Stepping Up

As you continue to place and level your bottom row, you may notice you need to dig deeper and deeper to place a block that's level with your previous one. If this happens, you might want to consider stepping your wall up. (or down, depending on your landscape) To do this, stop your row and put gravel around the block. Instead of placing your next block alongside the previous one, place it on top positioning it exactly halfway. Fill underneath with gravel and level this new higher block. Then continue as normal.

Step 7: Moving Along

Once your first row is complete, straight, and level, fill the empty space behind your wall with gravel. Now lay your landscape fabric on top of your block and place your second row of blocks on top so they hold the fabric down. Make sure you stagger the blocks.

Step 8: Gravel/Dirt

Place gravel against your wall inside your landscape fabric until it almost reaches the top of your wall. Then place dirt on the other side to bring up the ground to the same height. Once they are even you can place the next row of bricks. After that row is complete, repeat your gravel and dirt filling.

Step 9: Caps

If you want your wall to have a finished look, you will want to add caps to the top. Caps are just a solid concrete block with no lip that you will glue with adhesive to the top of your block.

Step 10: DONE!

Now's the time to step back and admire your work! If you have any questions or tips, please feel free to add them to the comments.

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20 Discussions

Very fine instructable and you've done a nice looking job with the blocks, especially over such a length.

I would like to say, especially if people are tempted to go bigger scale, this isn't really a retaining wall. A retaining wall will normally have a high newton block/reinforced concrete wall, often with piers, sitting on a reinforced foundation, even a low one, with (if required) a fair-face wall sitting in front. The wall will also have weep holes to prevent the build up of water behind the wall. This would be suitable in a 'home context', when you start to get a bit more serious, then different techniques are usually employed.

They are interesting blocks that you've used, easy to create curves without cuts. It looks like you've pointed the wall. I'd be inclined to take a drill and add some weep holes, especially lower down.

Generally speaking, the above may be fine for a rustic terrace in a garden, but if it's intended to prevent erosion of soil from the footing of the building, then I'd suggest a more robust structure, especially if the ground-slope had been changed. You may not notice the erosion since it's normally a slow process. Your first indication will be cracks within the building. If you are simply creating a terrace by adding soil to the original horizon, then you may well be okay, especially if this is not a new-build and the ground is stabilized. Remember that soil can easily contract and swell 10% between wet and bone dry!

Don't underestimate the forces involved. Nature wants everything flat!

I can't tell from your photo, but for others looking at your instructable, the line shouldn't touch the wall, but stand off by a few mm, you can set that with a thin lath if wood etc, or you can buy tingles that automatically hold the line off. An experienced bricklayer will usually wind his line around a couple of bricks and set the distance by positioning the brick. If you build any wall longer than your level/straight-edge, you should use a line. In addition to a boat level, and a bricklayers level, a line-level is very useful, and make a habit of rotating your level 180 deg each time. This indicates a build up of dirt under the level.

3 replies

Thanks for this comment, I am interested in building a retaining wall to actually terrace out my backyard so this is good to know.

Thanks for the feedback! It certainly seems like you know about walls. What do you mean when you say "pointed the wall"? In my case the back of the wall is all gravel and protected from soil intrusion by the fabric barrier. I think it would be very difficult for water to build up behind the wall. My line is a few inches above the block and I was lining it up by eye making sure all block edges were directly hidden from my view by the line, so I positioned the camera the same way I was eyeing the blocks. I appreciate all the info. Very helfpul stuff!

I should start by saying that I wasn't denigrating anything you've done, I was trying to catch people from assuming too much from (any) instructable. It would be horrible if someone's house was damaged. I suppose the moral would be "take local professional advice", but I'm all for DIY and skills not being in the domain of the few. If I didn't make it clear before, you've done a good job!

Pointing is the application of a water tight (often cosmetic) grout (cement) between the joints on the face, and finishing it in some way (lots of styles, especial on stonework). e.g. it may be recessed, flush, exposed, flat, angled, curved (convex or concave), polished or brushed etc. Often a style will be associated with a locality. Locally we have raised 'snail' pointing on locally quarried stone something like this, but less angular pointing

It's not clear from the images if your wall is pointed. Pointing will hold back any water behind the wall. Your wall is on a gravel bed and so should cope with drainage, depending on the properties of the barrier. Pointing tends to be hard (brittle) and so will not cope with movement.

The line is usually pulled taught at the height of the course being laid and a few mm from the face. Your work should never touch the line. If you were doing anything more complicated, then you would use a "story stick" too. Makes life so easy!

Layout This guy demonstrates some of the techniques quite well and shows the use of a story stick.

I had to learn all the trades, from groundwork to setting finials on a roof and everything between! Even now I'd say that I could give any of them a fair bash. My brickwork isn't really for fair face work and very slow ;) My plastering is acceptable, carpentry & plumbing is good. I hate painting, I can't tell you how many Georgian and sash windows I've painted. I always used to try to do electrical work, as it's one of the cleanest, driest, warmest trades :D

None of the trades are difficult if you break them down, but much easier with hints from a skilled practitioner, and of course you need to be aware of planning and building regs, the law etc.

Great job! Thanks for sharing!


8 months ago

I'd worry about the wall shifting, over time.

It's usual to place deadman anchors or tiebacks to support a retaining wall.

1 reply

Thanks for mentioning this, it's a good point. I did look into this a little bit and decided that because my wall was relatively low and therefore holding back a relatively small amount of dirt, that just the block would be enough. I think in the tallest parts hold back about 20 inches of dirt. But yes a taller wall would almost certainly need something like that. (mine still might but only time will tell)

I would've tried to use Mechanically stabilized earth, but if the load is not that big i guess its fine. I really loved the youtube video about Mechanically stabilized earth and this could be the time to try it.

Love it. Great detail.

Great job. Thanks for the inspiration! I have some foundation which is most likely due to footing issues around the garage work that looks like needs to be completed in the future . I've been thinking about a retaining wall design almost exactly like this as one of the options. I was thinking more for gardening mo... still... thanks for sharing.

Nice project and presentation ! I like to leave the lip on the first course of blocks. I think it adds to the block's "bite" into the gravel.

1 reply

Thanks for the feedback. This was my first wall, so you may be correct about that. I suppose I'll find out after a few harsh winters if my construction is good enough, lol.

It isba neat work. A little cement mortar between blocks could have increased the strength of the retaining wall.

2 replies

most retaining walls are "dry stacked" mortar = maintenance. Since the wall is not on a foundation below the frost level, it must have the ability to move as the soil moves from freezing and thawing.

I'd also like to add that in some areas the addition of mortar would classify it as a "permanent structure" and would require a building permit.


8 months ago

Very well done! When I first saw the photos I was thinking to make a comment about leaning the wall back by staggering the blocks, but discovered you did that (with the lip) ! Great observation about why you didn't use mortar and shouldn't unless it's a large wall with a deep poured concrete foundation. You could leave the lip on the first course though. The gravel (or sand) in the bottom should easily conform around it.

Love it! Nice 'ible, and great results, from the looks of it! Well done!

Nice instructions. I would use a longer level that spans 3 blocks but that's just me. Looks great!


8 months ago

Nice job and professionally done. No mortar means you left weep holes which relieves the water pressure behind the blocks. This is really important if the wall is higher, as height creates more water and more pressure. You did a great job and obviously did your research.

Nice result, and clear, well laid out instructions. Having recently watched several youtube videos on this topic, I have to say your instructable is easily the most approachable and gives me the confidence that I could actually do it... AND get good results..