How to Fix a Rotted Wood Retaining Wall (And Why Polyurethane Can Help)

Wood retaining walls are a popular choice for homeowners thanks to their natural look, affordability, and easy installation. However, wood is vulnerable to rot, insect damage, and moisture decay, especially in wet or humid environments. Compared to concrete retaining walls that last 50-100 years or more, wood retaining walls have a lifespan of just 15-40 years. If your home has a wood retaining wall and you’re starting to see bowing, leaning, or chunks of rotted wood, it’s time to take action.

Foremost Foundations and Construction offers wood retaining wall repair. We follow a tried-and-true process that ensures all damaged wood is removed, drainage issues are corrected, and the soil is stabilized. Our team will determine the best repair method once we assess the damage. Below is a step-by-step process on how to fix a rotted wood retaining wall, and why polyurethane foam injection may be a smart part of the repair process.

Step 1: Assess the Damage

Wood retaining walls don’t last forever. The first thing to do is inspect your wall carefully. Look for signs such as:

• Soft or crumbling wood

• Bowing or leaning sections

• Gaps between boards

• Soil erosion behind the wall

• Drainage problems nearby

If the rot is isolated to one section, you may be able to replace individual boards. But widespread rot likely means you'll need a partial or full rebuild.

Step 2: Improve Drainage

One of the biggest causes of rot in retaining walls is poor drainage. Before making repairs, make sure to address this. For instance, make sure gutters and downspouts direct water away from the wall, not toward it. The wall will also benefit with a gravel backfill and a drainage pipe or weep holes. This ensures you eliminate standing water or soggy soil around the base. Proper drainage prevents future rot and improves the longevity of any repair.

Step 3: Replace Damaged Wood

If the structure is still sound, you may be able to remove and replace rotted boards, reinforce weak areas with pressure-treated lumber, and use galvanized lag screws or rebar pins to stabilize loose sections. Always use pressure-treated or rot-resistant wood (like cedar or redwood) for replacements.

Step 4: Use Polyurethane Foam to Stabilize the Soil

Once you've repaired the wood, don’t forget to address what caused the movement or damage in the first place, such as unstable or eroded soil behind the wall. This is where polyurethane foam injection comes in.

With this type of repair method, small holes are drilled behind the retaining wall. Polyurethane foam is then injected into the soil, where it expands and fills voids and compacts loose soil. This creates a waterproof, dense support layer that helps stabilize the wall and reduce future erosion.

Poly injections are especially helpful when rebuilding the entire wall isn’t feasible, or if you're looking for a long-lasting way to reinforce and extend the life of the wall you just repaired.

Bonus Tips: Protecting the New Wall

To keep your new or repaired retaining wall in good shape, we recommend applying a waterproof sealant to exposed wood, regularly checking and clearing out drainage systems, and monitoring for signs of erosion or wall movement. You can also look into landscaping that helps divert water away, such as dry creek beds, swales, permeable paving, and French drains.

When to Call a Pro

If your retaining wall is severely leaning, has collapsed sections, or is holding back a significant slope, it’s best to call a professional. Structural issues, especially those involving soil movement or drainage correction, may require more advanced repairs, such as rebuilding the wall with steel-reinforced materials, installing helical tiebacks, or injecting polyurethane to stabilize and lift the surrounding ground.

Wood Retaining Wall Repair in Mississippi

Fixing a rotted wood retaining wall isn’t just about replacing a few boards; it’s about addressing the underlying causes and ensuring long-term stability. With the help of polyurethane foam injection, you can strengthen the soil, improve drainage, and restore your wall with confidence.

Foremost Foundations and Construction builds and repairs retaining walls in Central and South Mississippi. Most homeowners notice when their retaining wall needs repair, but we’re always happy to perform a thorough inspection. This way, you’ll know exactly what you’re dealing with and your options for repair. To schedule a free inspection, contact us today at 601-405-1052.