How To Build a Retaining Wall

Retaining wall construction is like most home improvement projects. It is never as easy nor as difficult as expected. In theory, it is all about laying a bunch of blocks until you reach the desired length and height.

However, in practice, building a retaining wall is much more complex. After all, you are trying to retain soil, a heavy material, especially when wet. Plus, the retaining wall will also be subjected to other elements like wind, water and freeze/thaw cycles.

Therefore, it takes a lot more planning, technique and effort to build a retaining wall that is stable, long-lasting and aesthetically pleasing. Any less, and the wall won’t last. It may even pose a danger to life and property.

Fortunately, all you need to build a retaining wall are some DIY experience, an understanding of the process and a good guide. You probably already have that first factor covered.

As for the second factor, an understanding of how to build a retaining wall, we can sum it up into four aspects:

• build a good base
• get the right building materials
• lay the blocks or bricks in a way that will result in a solid structure
• then add a drainage system

As for the guide (the third factor), that’s where this article comes in. So keep reading if you want to know how to build a retaining wall with blocks, bricks or any other material.

However, before we take you through the steps, here are the supplies needed for this project.

• The blocks or bricks: These could be concrete, natural stone, clay or even timber etc. More importantly, the blocks could be hollow or solid. The latter is sturdier but also heavier and more expensive. Finally, you can build a retaining wall with either stackable or interlocking blocks. It all depends on your preferences and circumstances.
• Jointing mortal or adhesive: to bind the blocks together and thus create the wall.
• Crushed stone or gravel: to provide a base and backfill for the retaining wall 
• Stakes and strings: For marking the site
• Measuring tape
• Excavator or/and shovel: for digging and excavation
• A mechanical compactor or hand tamper
• A spirit or bubble level
• Perforated drain pipes: for the drainage system 
• Landscape fabric
• Brush or broom
• Block splitter or mason saw

Now that we have listed the supplies, here is how to build a retaining wall with bricks or blocks in just ten steps.

Step 1: Choose and prepare a site for your retaining wall

You probably already have a place in mind. So let’s focus on the preparation aspect.

Firstly, you need to ensure that there are no utility pipes or cables on the site. If there are, you will need to relocate them or choose a different spot for your retaining wall.

After choosing a location, the next step is to set markings for the dimensions of your retaining wall. Simply use strings and stakes to mark the length. Alternatively, you can use a white powdery substance. The point of these markings is to give yourself a guide for digging the trench.

Step 2: Dig the trench

For this step, you need to use the excavator or shovel and dig a trench along the markings set earlier. The trench doesn’t have to be of any specific width or depth. However, here is what experts recommend.

• The recommended width for the trench: It should be wide enough to contain the blocks and leave extra spacing for the backfill and the drainage pipes. For specific figures, make the trench at least 3 to 4 inches wider than the building blocks.
• The recommended depth for the trench: It should be deep enough to contain 4 to 6 inches of base material and a foundation layer (of blocks) that is one-eight of the desired height for the retaining wall. For example, if the desired height of the retaining wall is 2 inches (24 feet), the recommended depth for the trench should be 4 to 6 inches plus 3 feet.

Step 3: Level and compact the trench

Don’t build a retaining wall (or any structure) on loose soil. If you do this, the wall could be prone to settling, shifting and cracking. For similar reasons, you also shouldn’t build on uneven grounds. It will be challenging to lay the building blocks evenly and the retaining wall will become prone to shifting and bulging, among other issues.

Try to even out and compact the trench before moving to the next step. Use the mechanical compactor or hand tamper for this. Then use the spirit level to measure evenness.

Step 4: Add the base material

Now it is time to build the base for your retaining wall. For this, most people use crushed rock or gravel. However, you can also use poured concrete and reinforced steel. The first two are the best options. Between them, experts often recommend crushed stone. It is easier to compact, more durable and better for drainage.

Whatever material you choose for the, ensure the sub-base is at least 4-6 inches deep. Don’t forget to compact and level too.

Step 5: Lay the first layer of blocks

Before taking this step, please ensure that the base is level and compact. As stated earlier, you shouldn’t lay blocks (to build a wall) on loose and unleveled soil. If this first block layer is crooked, the remaining layers and the entire retaining wall will be compromised.

So follow these tips.

• Use sturdy and strong blocks: You can cut or chip off weak or unnecessary parts before using a building block.
• Make sure the blocks align perfectly on all four sides.
• Start laying the blocks from the edge/end of the wall: This could be the edge that is most visible or the one closest to an adjacent structure.
• Lay the blocks close to the middle of the trench. This leaves space to add backfill on both sides.
• Complete this first layer/row of blocks before thinking of the next layer. Likewise, complete each layer before adding another layer on top.  

Follow those tips as you complete this foundational layer of blocks. Make sure the blocks align before securing them together. You can use the spirit level to measure this alignment and evenness. When you are satisfied, add the jointing mortar or adhesive. For interlocking blocks, you may need a plastic or rubber mallet to knock the fittings/grooves into place.

Step 6: Add backfill

Backfill provides extra support. We recommend using crushed stone or gravel. However, whatever the choice of material, don’t forget to level and compact.

You need to backfill the retaining wall to (or almost to) grade level. However, for now, only backfill the first layer of blocks. You will backfill the rest after installing the drainage pipes.

Step 7: Lay the remaining layers of blocks

Follow the same tips you did in Step 5 along with the following.

• Complete each layer before starting the next.
• Lay the blocks in a staggered pattern. The ends of each block should be at the centre of the ones above and below it. To achieve this, you may need half-sided blocks, especially at the edges. Check the tips section for info on how to cut blocks.
• Incline each layer backwards a little bit, like narrow stairs. This increases the structural integrity of your retaining wall.
• Clear the blocks’ surfaces before adding adhesives. Sediments like pebbles and sand can make the adhesive less effective. Water does the same. So don’t apply adhesives on wet blocks.
• Add capstones once the retaining wall reaches the desired height

Step 8: Add the drainage pipes

This drainage system will protect your retaining wall from underground water. So, we highly recommend it, especially if the wall is taller than 2 feet (24 inches). 

Lay perforated pipes along the length of the wall. Then provide an opening/outlet for the drain water. For ease and convenience, put that outlet at the edges.

Step 8: Add backfill to near-grade level

It’s time to backfill again. You can still use crushed stone and gravel. However, we recommend using breathable material. It is less likely to interfere with the flow of water. Examples of breathable materials are pea gravel and sand.

Backfill to or almost to grade level. Compact, level and cover with landscape fabric.

Step 10: Finish

Now it’s time to cover the backfill with topsoil so you can plant turf in the area. 

Tips for building a retaining wall with blocks or bricks

Before we end this article, here are three more tips.

How to cut blocks

For minor chips, use a hammer and chisel. However, you need a block splitter or a mason saw to cut blocks into smaller sizes. 

You can make marks for smoother and easier cuts. Use grease pencils, soapstone pencils or markers for this. You can also wet the blocks (before cutting) to reduce dust and

Apply the adhesives properly  

First of all, use an adhesive that is recommended for the building material. Within block layers, add the adhesive to the side of just one block, then press the other block to it. Between layers, add the adhesive to the top of the block below, then press the above block to it.

As always, remember to align the blocks and clear their surfaces of sediment before applying adhesive.

Build a multi-tiered retaining wall instead of a tall one

The tall retaining wall is more complex and prone to structural instability. It may also require building permissions. For a gravity retaining wall like this, we recommend a height of 3 feet as the cut-off point. It’s better to build a tiered retaining wall instead of passing that height. 

It will cost more but structural stability and aesthetics will improve. For more information, read this- What Are the Main Types of Retaining Walls?

Conclusion

There are a lot of benefits to building a retaining wall in your garden. It reduces erosion and adds aesthetic value, a focal point and usable space. We hope this article will encourage and help you build the retaining wall you want. 

We have to end this now, so here is an article on retaining wall ideas.