Updated on June 2, 2023

Do it yourself

How to Build a Concrete Retaining Wall with Blocks

If you have a steep slope or a decorative garden that needs a sturdy base, a retaining wall could be the perfect solution. Check out our step-by-step guide on how to construct your own retaining wall and transform your outdoor space into a low-maintenance, visually appealing area.

Difficulty level: Intermediate

Duration: 1 weekend

Before You Start

Many different materials can be used to build a retaining wall: wood, stones, or concrete blocks. Over time, wood will rot and stones may fracture. However, if it is well built, a concrete wall will remain beautifully intact for a very long time.

When determining the number of blocks for your wall, keep in mind that curved walls will require more blocks than straight walls. Additionally, you should have the pallets of blocks left on the street rather than the driveway when delivered, as the weight can cause damage to the pavement.

Material

Interlocking Retaining Wall Blocks Retaining Wall Blocks Cotton String Stakes Landscaping Fabric ½" Washed Gravel 0 – ¾" Gravel Construction Adhesive

Tools

Shovel Rake Level Caulking Gun Broom or Brush Safety Glasses Dust Mask Chisel Rubber Mallet Tamper Gloves

Benefits of Interlocking Retaining Walls

Interlocking concrete retaining blocks are easy to assemble as they don’t require mortar or rebar reinforcement. They feature a lip on the back that locks the blocks together, with the cavity behind the wall pushing the blocks forward, strengthening the joints. The blocks taper from the front face to the rear, making it easy to form curves. Best of all, they can be dismantled and rebuilt if mistakes are made or if you change your mind about the wall’s location or shape.

Interlocking concrete retaining blocks are not suitable for tall walls and should only be built to a maximum height of 15-28”, but they are a fantastic option for low walls, terraces, and raised beds. A terraced system provides excellent erosion control and ample landscaping opportunities.

Retaining Wall Trench and Foundation Building Tips

To ensure a sturdy retaining wall, it’s important to start with a good foundation. Begin with a level base of blocks, partially below ground for a firm hold in the soil, and ensure that each subsequent course is also level.

For properties that have a slope, the foundation trench may have to be dug in a series of steps the height of the blocks. Use blocks to build up the lower sections until you can add courses of blocks to the stepped areas for a seamless and level wall.

With a solid foundation trench in place, the blocks can be laid. The level support of the base and the partially buried foundation course will help prevent the wall from moving, ensuring its durability and stability over the long term.

1
Mark and Measure

1.1Use stakes and cotton string to mark the key points and measure out the area for your wall.
1.2Provide a minimum 12" space at the back of the wall for ½" drainage gravel, and 12" at the front to support the wall.

2
Dig the Trench

Dig a 6" deep trench, allowing an additional 10% of the height of your wall as additional depth. This will let you lay the blocks into the soil.

Person using a hand tamper to compact soil

3
Tamper and Smooth the Soil

3.1Use a hand tamper to compact the soil in the trench. If you find it physically challenging or uncomfortable, you can drop the tamper from a height of approximately 9" and let gravity do the work for you.
3.2Use a rake to gently loosen the soil in the trench, making sure it is not overly compacted. Then, use a level to ensure a flat surface, and rake the soil around to remove any bumps or dips.

Person adding landscaping fabric to a trench

4
Line the Trench

4.1Use porous landscaping fabric to line the trench and keep soil from seeping between the blocks.
4.2Starting at the trench base, unroll the fabric long enough so that it overlaps where the top course of blocks is going to go.
4.3Cut the fabric to size and continue lining the trench until it is fully covered. It should be longer than the height of the wall by at least 12"; you’ll use the extra length to cover the drainage gravel.
4.4Keep the landscape fabric in its intended position while making final adjustments to the blocks by using stakes to anchor it firmly in place. This will ensure that the fabric lines the trench as initially planned.

5
Make the Foundation

5.1Spread 6" of 0-¾” gravel over the entire surface of the landscape fabric. This will facilitate proper drainage, preventing prevent water pressure from accumulating behind the wall and causing possible failure. As all retaining walls are subjected to water force, whether it’s from unexpected incidents or heavy downpours, proper drainage is essential to maintain integrity.
5.2Use a mechanical compactor to compact the gravel, and make sure that the foundation for the first row of blocks is level.
5.3Place 1" of stone dust and compact again.
5.4Firmly tamp down the stone dust and use a rake to even out any irregularities.

Person removing flanges from retaining blocks

Level placed on a row of concrete blocks

6
Install the Base of the Wall

6.1If the retaining blocks you are using have flanges, then remove the flanges from the first course of blocks using a hammer and masonry chisel to ensure a level placement.
6.2Lay the first row of blocks, making sure they’re level.
6.3Wearing gloves is recommended to protect your hands.
6.4For any blocks that aren’t level, use a rubber mallet or the butt end of a hammer to give it a tap. Add a small amount of gravel as needed.
6.5Keep laying the foundation course, ensuring that all blocks are partially buried and level.
6.6Install a 4" diameter perforated drain pipe behind the wall in line with the base.
6.7Make sure that the drain pipe has a suitable outlet, usually towards the lowest point of the wall. You can conceal it by covering it with gravel or river stones.

Pro Tip

Levelling is crucial for the strength and stability of a retaining wall, preventing it from tipping forward. Failing to level the base can lead to an increasingly unstable wall with each course added. Correcting errors early on is much easier than attempting to fix them later, so starting with a level base is key to a durable and long-lasting construction.

Person cleaning a cement block with a brush

Person tracing a line on a concrete block

Cinder blocks placed in a staggered pattern

7
Begin the Second Course

7.1For the second course, ensure that the first block is staggered in a brick-like pattern by cutting it in half lengthwise. This will provide strength and stability to the wall. However, be sure to wear eye protection when cutting the block. If an angle grinder is used, hearing protection and a dust mask are also necessary.
7.2Place the remaining blocks of the second course, ending with the remaining half of the initial block you have cut.
7.3Before adding more courses, ensure that the row of blocks is level and adjust any areas that are not.

8
Lay the Remaining Rows

8.1Lay the following rows in such a way as to make the joints overlap.
8.2Backfill the back of the wall with ½ " gravel after installing every second row. The first backfill should cover the perforated drain located just behind the first row. This should be done manually, not machine compacted.

Pro Tip

Be sure to regularly clean each block to prevent dirt or gravel from getting trapped between courses, which can cause unevenness and instability.

Person applying adhesive onto concrete blocks

Concrete retaining wall with a raised flower bed

9
Complete the Installation

9.1Perform a final check on all courses with a level to ensure they are even. If needed, gently nudge the blocks into place with a mallet or hammer until they are aligned.
9.2After finishing the courses, be sure to thoroughly sweep away any dust or debris from the top of the blocks.
9.3Once the surface is clean, apply construction adhesive to secure the last course to the wall or wall caps.
9.4Fold the geotextile sheet over the drainage gravel.
9.5Cover the geotextile sheet with native soil from your property, black earth, or another material, and rake the material to smooth it out, ensuring that it isn’t too compacted.
9.6Do the same for the gravel at the base of the wall
9.7Lay the cap blocks on the top if needed.
9.8Replace the strips of sod and water the grass.

Disclaimer

These DIY projects are provided for informational purposes only. The information contained in RONA’s DIYs is intended to provide general guidelines to simplify jobs around the house. Because tools, products, materials, techniques, building codes, and local regulations are continually changing, RONA inc. assumes no responsibility for the accuracy of the information contained herein and disclaims any liability for the omissions, errors, or outcome of any project. RONA inc. makes no representation on the feasibility of any project and the viewer bears all risks coming with the realization of the projects. It is the responsibility of the viewer to ensure compliance with all applicable laws, rules, codes, and regulations for a project. The viewer must always take proper safety precautions and exercise caution when taking on any project. If there is any doubt in regard to any element of a project, please consult a licensed professional.

How to Build a Concrete Retaining Wall with Blocks

Benefits of Interlocking Retaining Walls

Retaining Wall Trench and Foundation Building Tips

1
Mark and Measure

2
Dig the Trench

3
Tamper and Smooth the Soil

4
Line the Trench

5
Make the Foundation

6
Install the Base of the Wall

Pro Tip

7
Begin the Second Course

8
Lay the Remaining Rows

Pro Tip

9
Complete the Installation

Disclaimer

Suggested Products

Gazebos and pergolas

Outdoor power equipment

Barbecues and smokers

How to Build a Concrete Retaining Wall with Blocks

Benefits of Interlocking Retaining Walls

Retaining Wall Trench and Foundation Building Tips

1Mark and Measure

2Dig the Trench

3Tamper and Smooth the Soil

4Line the Trench

5Make the Foundation

6Install the Base of the Wall

Pro Tip

7Begin the Second Course

8Lay the Remaining Rows

Pro Tip

9Complete the Installation

Disclaimer

Suggested Products

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1
Mark and Measure

2
Dig the Trench

3
Tamper and Smooth the Soil

4
Line the Trench

5
Make the Foundation

6
Install the Base of the Wall

7
Begin the Second Course

8
Lay the Remaining Rows

9
Complete the Installation