How To Rebuild a Concrete Block Retaining Wall

Retaining walls are a critical part of your landscape, keeping soil in place and preventing erosion. Like any outdoor structure, they can start to show signs of wear and tear over time, which can create safety concerns and impact your home’s curb appeal. Rebuilding a concrete block retaining wall is a big job, but with the right planning and execution, you can restore its strength and appearance. In the video above, This Old House mason Mark McCullough rebuilds a failing retaining wall that was stacked with the wrong material.

Signs of a Failing Retaining Wall

Retaining walls can fail for many reasons, such as poor construction, inadequate drainage, or improper materials. Recognize the signs of a failing wall to help you address issues before they snowball into bigger problems. Here are several telltale signs that indicate your retaining wall is failing and needs repairs or replacement.

• Material displacement or overall instability: When the wall’s materials shift or the structure becomes unstable, it suggests foundational problems or external pressure that the wall can no longer support. This can lead to partial or total collapse if not addressed promptly.
• Leaning or tilting away from its original position: A retaining wall that leans or tilts indicates that it’s no longer structurally sound, possibly due to inadequate drainage or soil movement. This shift can compromise the wall’s ability to hold back soil and maintain its intended shape.
• Separation between wall blocks or bricks: Gaps forming between blocks or bricks suggest that the wall is under stress or that the mortar is deteriorating. These separations weaken the wall’s integrity and can lead to further damage.
• Visible cracks or bulges in the wall structure: Cracks or bulges are signs of structural failure due to excessive pressure, water damage, or poor construction. These defects can expand over time, leading to safety hazards.
• Water seepage or soil erosion behind the wall: If water seeps through or soil erodes behind the wall, it indicates inadequate drainage and potential water pressure buildup. This condition weakens the wall’s stability and can accelerate its deterioration.

Preparing for the Retaining Wall Project

Before you start rebuilding, prepare the site and gather the necessary materials and tools. Detailed planning and preparation will make your project more successful in the long run.

Site Preparation

Site preparation gives you a solid foundation for your new retaining wall and protects the surrounding area. Follow these steps to prepare your site:

1. Remove any plants lining the retaining wall using a shovel. Dig deep to preserve strong root balls.
2. Transfer plants temporarily to a tarp for safekeeping.
3. Carefully dismantle and remove the pieces of the old wall.
4. Dig a few inches back and deep along the location of the old wall to create a clean workspace.
5. Ensure the area is free of debris and obstacles that could impede construction.

Materials and Tools Needed

Here’s what you’ll need to rebuild your concrete block retaining wall:

• Concrete retaining wall blocks
• Construction adhesive
• Gravel for drainage
• Landscape fabric
• Level
• Perforated drainage pipe
• Rubber mallet
• Safety gear, including gloves and protective eyewear
• Shovel
• Tamper
• Wet tile saw (if needed for cutting blocks)
• Wheelbarrow

Building the New Concrete Retaining Wall

With the preparation out of the way, it’s time to move on to the construction phase. This step-by-step guide will walk you through each stage to help you build a sturdy retaining wall. Every phase of construction is crucial to the wall’s overall success and durability.

Creating a Solid Foundation

Ensuring a level base will prevent shifting and settling over time. Follow these steps to create the base:

1. Lay a thick base of gravel along the trench, packing it down tightly with a tamper.
2. Place the first course of blocks about halfway deep in the trench.
3. Set one block every 6 feet or so along the length of the wall, leveling them to one another.
4. Fill in the rest of the wall, using a rubber mallet to secure the blocks in place.

Installing Drainage Systems

McCullough emphasizes the importance of this step to help with drainage, which prevents water buildup and potential wall failure. This drainage system will help maintain the wall’s stability and prevent seepage and erosion issues.

1. Lay a fabric liner along the back and base of the wall to prevent soil contamination.
2. Backfill behind the first course with more gravel to promote drainage.
3. Install a perforated plastic pipe behind the wall, and backfill it with gravel.

Building Subsequent Courses

With the foundation and drainage in place, you can start constructing the higher courses of the wall.

1. Lay the next course of blocks, lining up the channels using the channel connectors.
2. Ensure that face joints don’t overlap for added stability.
3. Continue backfilling with gravel behind each course.
4. Repeat the process until the wall reaches the desired height.
5. Periodically check for level and alignment to ensure uniformity.

Finishing Touches

These finishing touches will give your retaining wall a polished and professional look:

1. For the top course, apply construction adhesive to secure the cap blocks.
2. Carefully place the cap pieces, and even them out with a rubber mallet for a polished look.
3. Once the adhesive has set, return any plants to their positions near the wall.
4. Inspect the wall for any remaining gaps or imperfections and make necessary adjustments.

FAQ About Retaining Walls

When rebuilding a retaining wall, homeowners often have questions about the process. Here’s how to address some of these common problems and retaining wall questions.

How can you fix a deteriorating retaining wall?

The best way to fix a deteriorating retaining wall is often to rebuild it entirely, as demonstrated in this project. This ensures that all the underlying issues are addressed and that the new wall is built to last. Rebuilding also allows you to use modern construction techniques and materials for a more durable result.

How much does it cost to rebuild a retaining wall?

According to Angi, it costs an average of just over $6,072 to rebuild a retaining wall or replace it entirely. Building the retaining wall yourself can save you $15–$50 per square foot in labor costs.

How can you strengthen an existing retaining wall?

While rebuilding is often the best solution, you can sometimes make minor reinforcements to an existing wall. These can extend the wall’s life and address specific weaknesses, though they’re typically temporary. Here are some strengthening strategies:

• Adding proper drainage systems: Installing drainage solutions, such as weep holes or gravel backfill, helps to reduce water pressure behind the wall. Drainage can prevent water buildup, which is a common cause of wall failure due to erosion and hydrostatic pressure.
• Installing tiebacks or anchors: Tiebacks or anchors provide additional support by connecting the wall to stable ground behind it. This can help stabilize a leaning or bulging wall. This reinforcement method helps counteract the forces pushing against the wall, adding extra stability.
• Repairing small cracks or gaps with masonry adhesive: Using masonry adhesive to fill minor cracks or gaps can help maintain the wall’s appearance and prevent water infiltration. Although this is a temporary fix, it can slow down the deterioration process by addressing surface-level issues.

What’s the lifespan of a retaining wall?

A well-constructed concrete block retaining wall can stand strong for 50–100 years. Your wall’s longevity depends on several key factors, such as your material quality, installation techniques, effective drainage systems, and consistent maintenance.

Tips for Success When Building a Retaining Wall

To ensure your rebuilt retaining wall stands the test of time, use crushed stone instead of rounded gravel for a more stable base. Crushed stone makes the best base for walls because the stones’ sharp, angular edges lock together when tamped and provide excellent drainage. Gravel contains weathered stones that are more rounded and difficult to compact.

Before starting your project, research local building codes and permits. Consult with professionals if you encounter complex issues or need expert advice.

Retaining Wall Landscape Integration

Integrating your new retaining wall into your landscape involves thoughtful planning and design. Here’s how to ensure it blends seamlessly with your surroundings:

• Select compatible plantings: When replanting around your new wall, choose plants that thrive in your local climate and soil conditions. Look for low-maintenance perennials, native shrubs, and erosion-controlling groundcovers.
• Add decorative elements: Incorporate decorative elements to make your retaining wall more attractive, such as outdoor lighting, garden ornaments, mulch, and decorative rocks.
• Maintain the wall and its surroundings: Regular maintenance helps your retaining wall stand the test of time. Inspect for and address drainage issues promptly. Remove debris and plant overgrowth regularly and periodically check for structural integrity.