How Polyurethane Injection Repairs a Seawall Without Excavation

When a seawall has voids behind it — cavities in the soil created by water erosion — the traditional repair required excavating behind the wall, adding new fill material, and waiting for settlement. That approach takes days, disturbs your yard, potentially requires dock removal, and costs significantly more than modern alternatives. Polyurethane injection changes all of that.

What Is Polyurethane Injection for Seawalls?

Polyurethane seawall injection uses a two-component expanding foam resin that is pumped through small holes drilled in the seawall panel. The two components mix as they're injected, triggering a chemical reaction that causes the foam to expand — up to 25 times its liquid volume — filling every void in the soil behind the panel. Within 15–30 minutes, the foam cures to a rigid, closed-cell, waterproof mass.

The Step-by-Step Process

1. Free inspection and void probe test — we identify the location and extent of all voids
2. Small-diameter holes (5/8") are drilled through the seawall panel at calculated locations
3. Two-component NCFI polyurethane is mixed and injected under controlled pressure
4. Foam expands through the void network, filling all cavities completely
5. Back-pressure monitoring confirms complete void fill at each injection point
6. Ports are plugged with marine-grade stainless steel fittings
7. Post-treatment probe test confirms structural restoration

Why NCFI-Certified Materials Matter

Not all polyurethane foams are equal. Consumer-grade spray foam (like what you'd buy at a hardware store) is not suitable for seawall applications — it lacks the density, compressive strength, and saltwater resistance required. NCFI's marine-grade polyurethane formulations are specifically engineered for subaqueous and coastal applications, with compressive strengths of 25–50 PSI and zero water absorption. As an NCFI-certified top installer, Solid Foundations uses exclusively NCFI-approved materials on all seawall projects.

What Polyurethane Injection Can and Cannot Fix

It CAN fix:

• Voids of any depth or geometry behind the seawall panel
• Cracking caused by void-related settlement (stair-step and diagonal crack patterns)
• Water seepage through panel cracks (sealing cracks before injection)
• Early-stage bowing (when combined with helical tiebacks)
• Settlement of hardscape or lawn near the seawall

It CANNOT fix:

• Structural movement that has already occurred — the foam fills the void but doesn't push the wall back (tiebacks do that)
• Shattered or fully fragmented panels that can't contain the expanding foam
• Corroded rebar (we can address this separately with epoxy injection and surface treatment)
• A wall that needs replacement — polyurethane buys time but isn't magic

Polyurethane Injection Cost vs. Replacement Cost

A typical residential void fill project costs $3,000–$15,000 depending on void volume. Full seawall replacement for the same wall costs $35,000–$80,000. When polyurethane injection can do the job, it represents savings of $20,000–$65,000 on a single project. The catch: not every failing seawall qualifies. That's why the initial assessment matters — we'll tell you honestly whether injection is the right solution for your specific wall.