Retaining walls are very important landscaping elements that you can use to hold back soil, rock and other materials on a steep slope to prevent soil erosion and protect the natural landscape of an area. The amount of soil these walls hold back can be pretty significant, that’s why choosing the right material to build them is even more important.
Talking about materials, we often get asked quite a lot by homeowners if they can use cinder blocks for building their retaining walls.
The simplest answer to that question is yes. Cinder blocks or large concrete blocks are made out of cement, aggregates, and sometimes fly ash, and they come in different sizes and shapes, making them very flexible for use in different applications.
They can be stacked together securely using mortar or adhesive to create a stable retaining wall structure. The hollow cores they have also provide opportunities for reinforcement with vertical and horizontal steel rebars and concrete, thus enhancing the wall’s strength and stability.
However, it’s important to consider the height, load requirements of the wall or how steep the landscape it’s holding back. It’s also going to depend on how far the wall will extend. Engineering considerations, such as proper reinforcement, drainage, and appropriate footing, should be taken into account to ensure the structural integrity of the retaining wall.
The steeper the landscape is or the longer the wall needs to be, the stronger the build material needs to be, or the more reinforcement it needs.
From small to medium retaining walls in your yard, or around your home, cinder blocks are an excellent choice of building material, because they’re durable, affordable, and they’re relatively easy to work with.
Steps to Build a Retaining Wall with Cinder Blocks
Planning and Design
The first step to building a retaining wall is to plan and design the type and style of the wall. You need to survey the landscape, considering factors such as the condition of the soil, and the type of drainage to install.
Before starting the project, remember to consult local authorities for building codes and regulations, as requirements may vary depending on where you live.
It’s also advisable to consult a professional builder if you have any doubts about the designs and how to implement them.
Gather Materials and Equipment for the Job
Since you’re using cinder blocks, the next step is to buy the amount of blocks you need for the job. You can calculate how many blocks you’ll use depending on the length and height of the wall, and the dimensions of the block.
This is also a good time to gather the tools you need for the job, such as shovels, mason’s trowel, level, string, tape measure, wheelbarrow, chalkline, pencil, striking tool, brick set, and story pole.
The materials for the build include cinder blocks, mortar mix, gravel, 2×4 and 2×8 lumber, landscape fabric, 3/4-inch pipe and perforated drainage pipe.
Site Preparation
Before any construction can take place, the site has to be cleared of any vegetation, debris and obstacles to ensure the the foundation can be built and the wall installed.
First you need to mark the boundaries of the area where the retaining wall will be constructed. Use stakes and string or spray paint to outline the shape and size of the wall. This will help you visualize the project and ensure accuracy during the clearing process.
After that, you can then clear away any vegetation, including grass, weeds, shrubs, or trees, within the marked area. Ensure to remove any roots to prevent regrowth that can potentially damage the wall in the future.
Excavation and Leveling
The next step is to excavate the area within the marked boundaries to prepare the foundation for the retaining wall. You need to remove any existing soil, rocks, or debris to create a level and stable base for the wall.
You also need to ensure that the excavated area is properly graded to allow for proper drainage away from the retaining wall. It should have a slight slope away from the way to prevent water from accumulating behind the wall, which can cause hydrostatic pressure and potential failure as time goes on.
After that, you need to dig a trench for the first row of cinder blocks. The trench should be wider than the blocks and deep enough to accommodate a layer of compacted gravel.
Lay the Foundation
The next step of building a retaining wall with cinder blocks is laying the foundation. It is typically built below the frost line to prevent frost heave and ensure stability.
Factors such as the height and type of the retaining wall, the soil conditions, and local building codes will determine the exact depth of the foundation.
The foundation is one of the most crucial component that supports the weight of the wall and transfers it to the ground. That’s why it’s very important that you consult with a structural engineer or a qualified professional to determine the appropriate depth for your specific project.
There are different types of foundations you can go for including: trench or strip footing, pile foundation, spread footing, and anchored foundation.
The type of retaining wall foundation you choose will depend on factors such as the height and type of retaining wall you want to build, the condition of the soil, your budget and recommendations from a professional/city codes (assuming you consulted one).
Build the Retaining Wall
Once the foundation is done, the next step is to start building the wall. Since you’re using cinder blocks for your retaining wall, you need to start placing the cinder blocks on the foundation in the trench.
Before that though, you need to prepare the mortar. You can mix it in a wheel barrow or a mixing tub until it reaches a consistency you can work with.
Next, you need to start applying the mortar to the footing or foundation you’ve made. If you have a concrete footing or foundation, apply a layer of mortar to the top using a trowel. This will help bond the first course of blocks to the foundation.
Lay the first course, starting at a corner until it is complete and repeat. Use a level to ensure that the blocks are level horizontally and vertically. Adjust the blocks as necessary by tapping them gently with a mallet or the back handle of your trowel.
You also need to stagger the placement of the cinder blocks in each successive row to chain them together and distribute the weight evenly across the wall.
Add Drainage Pipes
Proper drainage is essential for the long-term stability and effectiveness of a retaining wall. Without adequate drainage, water can build up behind the wall, increasing hydrostatic pressure and potentially causing the wall to fail.
The first step to add drainage to a retaining wall is to use a layer of gravel or crushed stone to backfill the area behind the wall. This creates a drainage zone allowing water to flow freely and prevent buildup of water behind the wall.
Before adding the gravel, ensure to mat the ground behind the wall with geotestile fabric to prevent soil from mixing up or infiltrating the gravel layer.
After adding the gravel, install a perforated pipe on the gravel layer at the base of the wall. The pipe should have evenly spaced holes to collect water and transport it away from the wall. Then connect the pipe to a suitable drainage outlet to ensure proper water disposal.
Reinforce the Cinder Blocks
This may not be necessary for very low walls, but depending on the height, you may want to insert vertical and horizontal reinforcing grids or rebar into the cores of the blocks to further strengthen the wall.
Start Backfilling
Finally, you need to backfill the space behind it with suitable backfill material like soil or crushed stone. Remember to compact the fill material in layers to prevent it from collapsing later. Also ensure the mortar and reinforcement hardens first before backfilling and compacting, to prevent the wall from collapsing.
Once you’ve laid the cinder blocks to the required height, reinforced it and back-filled it, the final step is to finish the top surface with coping stones or cap block to provide a clean and finished look to it.
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