How To Build a Block Retaining Wall

Retaining walls serve multiple purposes in landscaping, from controlling erosion and managing water drainage to creating beautiful, functional garden spaces. Thanks to interlocking, stackable blocks, you can now easily build your own retaining wall over a weekend.

This guide will walk readers through the process of building a stackable block retaining wall, from selecting materials to finishing touches. Following these steps, you can create a durable, attractive retaining wall that improves your property’s form and function.

Understanding Stackable Concrete Blocks

Stackable concrete blocks are the foundation of most modern DIY retaining walls. These blocks feature a decorative finish on the front and a lip on the back, creating an interlocking system that provides stability and strength to the wall.

Their decorative front face, interlocking lip structure, and slight wedge shape make straight or curved designs easy. You can also purchase topper stones to create a finished look without the interlocking structure being visible on the top of the wall.

Today’s Homeowner Tip

Stackable stones are generally recommended for walls less than 3–4 feet high. Taller walls typically need additional structural reinforcement and may require a building permit along with professional advice or help.

Materials and Tools Needed To Build a Block Retaining Wall

Before beginning the project, gather all necessary materials and tools to have a smooth workflow and avoid delays during construction.

Essential Materials

You’ll need these materials:

• Interlocking stackable stones and toppers
• Gravel (sharp, not rounded) or rock dust
• Landscape fabric (optional)

Get at least one block per linear foot of wall. We recommend buying more blocks than you initially estimated since projects often require more materials than expected.

Required Tools

Here are the tools you’ll need:

• Work gloves
• Shovel and/or mattock
• Brick chisel and small sledgehammer
• Level
• Wooden stakes
• String and a line-level
• Soil tamper

Planning and Layout

The planning phase involves marking the wall’s location and checking that there are no underground utilities in the area.

Marking the Wall Location

Create the layout for your retaining wall:

1. Use a garden hose to outline the desired shape of the retaining wall.
2. Mark the ground along this line using flour or landscape marking paint.

This way, you can plan out where to build the wall and make adjustments before you begin.

Checking for Utilities

Before breaking ground, contact your local utilities office or dial 811 to verify that there are no buried pipes or cables in the planned digging zone. 

Digging the Trench

The foundation of a sturdy retaining wall begins with a properly prepared trench.

Trench Specifications

Here’s how to dig a functional trench:

1. Dig a trench slightly wider than the blocks, ideally matching the width of the soil tamper.
2. Make the trench deep enough so the first course of blocks will be below ground level.
3. Cut straight down with the shovel to avoid disturbing the surrounding soil.
4. Create a series of stepped trenches for walls across slopes to maintain a consistent below-ground depth for the first course of blocks.

Preparing the Base

Prepare the base with these steps:

1. Tamp down the bottom of the trench using a soil tamper.
2. Add several inches of sharp gravel or rock dust to the trench bottom.
3. Level and tamp this layer to create a solid foundation for the blocks.

Laying the First Course

The first course of blocks sets the stage for the entire wall. How careful you are with the first course majorly impacts the success and strength of the rest of the wall, so take extra time to perfect it.

Starting the Wall

Here’s how to start the wall:

1. Begin at the most visible edge or where the wall meets another structure.
2. For walls across slopes, start at the lowest point.
3. Position the first stone in the trench, ensuring it’s level from front to back and side to side.
4. Adjust by adding or removing gravel as needed to achieve proper leveling.

Establishing a Guide

To establish a guide:

1. Hammer wooden stakes into the ground at each end of the trench.
2. Stretch a string between the stakes, aligning it with the top of the first stone.
3. Use a line level to ensure the string is perfectly level.
4. Use this string to guide the rest of the first course.
5. Continue laying stones side by side along the trench, checking it’s level as you go.

Building Additional Courses

With a solid foundation, you can begin building the wall. This phase is where the retaining wall starts to take shape. Continue building up the wall to the desired height, topping it with capstones for a finished look.

Stacking Techniques

Follow these techniques when stacking the blocks:

• Offset each row of blocks from the one below for a stable and more natural look.
• Start the second course with a block cut in half for walls with straight edges to create a staggered pattern.
• Ensure the lip of each stone fits tightly against the stone below it for structural integrity.
• Maintain offset seams between courses for added strength.

Maintaining Level and Stability

Here are some tips for creating a stable and level retaining wall:

• Periodically check that stones are level and wobble-free.
• Use a level to verify both horizontal and vertical alignment for each course.
• Make adjustments as necessary by adding or removing material beneath the blocks.

Cutting Blocks

Occasionally, you may need to cut blocks to fit specific spaces or create half blocks for staggering courses. To cut a block in two:

1. Score a line around the middle of the block using a brick chisel.
2. Position the chisel on the scored line.
3. Strike the chisel firmly with a small sledgehammer to split the block.

Backfilling the Wall

Your wall needs proper backfilling to maintain its stability and drainage capabilities. It helps prevent water buildup behind the wall, which can lead to structural issues over time.

Backfilling Process

Here’s how to backfill the wall:

1. Spread landscape fabric against the back of the wall before backfilling to keep the wall clean and allow for proper drainage.
2. Add backfill material in layers. Place gravel directly against the wall to promote drainage and use fill dirt behind the gravel layer.
3. Firmly tamp down each layer before adding the next.
4. Finish with a layer of topsoil for planting or additional landscaping.

For walls intended to divert water runoff, place a perforated drain pipe against the back of the wall before backfilling. This improves the wall’s ability to manage water and reduces the risk of water-related damage.

Finishing Touches

Adding finishing touches to your retaining wall helps it look and work better. These elements can boost the overall look of the project and make sure it fits in seamlessly with the surrounding landscape:

Adding Capstones

Capstones cover gaps between the blocks and improve your retaining wall’s appearance. Here’s how to install them:

1. Select capstones that match the style and color of the stackable blocks used for the wall.
2. Lay the capstones along the top row. They should be evenly spaced and overhang slightly.
3. Secure capstones with landscape adhesive if necessary to prevent movement.

Landscaping Around the Wall

Thoughtful landscaping adds to the wall’s attractiveness and can help with erosion control. Here are some ideas:

• Plant low-maintenance shrubs or flowers along the base and top of the wall.
• Use mulch or decorative gravel to create a clean edge and prevent weed growth.
• Incorporate lighting for added safety and ambiance, particularly for walls near pathways or seating areas.

Maintenance Tips

Proper care can prevent common issues such as shifting blocks, erosion, and drainage problems.

Regular Inspections

Here’s how to inspect your retaining wall:

1. Inspect the wall periodically for signs of movement or damage, especially after heavy rain or frost.
2. Check for any leaning or bulging sections that may need attention or reinforcement.
3. Ensure drainage systems, if installed, are clear and functioning properly.

Addressing Erosion

Address erosion with these tips:

• Monitor the base of the wall for signs of erosion and reinforce with additional gravel or soil as needed.
• Maintain the landscape fabric and backfill material to prevent water buildup behind the wall.
• Consider adding ground cover plants or additional mulch to areas prone to erosion.

Cleaning the Wall

Follow these tips when cleaning your retaining wall:

• Clean the surface of the wall with a low-pressure garden hose to remove dirt and debris.
• Avoid using harsh chemicals that may damage the blocks or surrounding plants.
• If algae or moss growth occurs, use a mild detergent solution and scrub gently with a brush.