What can seawall foam injection fix?
Foam can fill a confirmed void behind a sound wall or seal a leaking joint. It does not repair a cracked panel, a failed tie rod or a wall that is still moving.
A typical foam job begins with a soft spot behind the cap. The installer drills a grid of small holes, sets tubes and pumps in resin that expands as it cures. Done well, the foam fills the gap and plugs the route the fill was escaping through.
Key West used foam on a public job. Its 2026 Navy Mole Pier repair pairs steel patch panels, welded underwater, with polyurethane foam grout to fill voids behind the wall. Key West ITB 26-002 The steel fixed the failed sheet pile; the foam filled the space behind it.
When should I call about seawall foam injection?
- A small sinkhole behind a wall that is straight and not cracked through.
- A sand stain or small fan at one joint at low tide.
- A void found by probing during an assessment.
- Not when the cap is out of line, the wall leans or the toe is exposed. Read tiebacks and anchors or riprap and toe protection first.
How do Keys seawalls change the foam question?
The common Key Colony Beach wall uses 6-inch concrete panels, a concrete cap and steel tie rods to a deadman. Weep holes and French drains let water out. KCB Seawall Owner’s Manual
Most of those walls were designed for a 30-year life, and many have passed it. KCB Seawall Owner’s Manual On an old wall, a void is often a symptom of rusted rods or open joints, not the whole problem.
The ground matters too. USGS says the Middle and Upper Keys are Key Largo Limestone, an old coral reef, and the Lower Keys are Miami Limestone, cemented ooids. USGS Keys geology Coral skeletons from that reef show in the walls of man-made canals. USGS Keys geology So a canal wall may stand against rock, against fill, or both.
Ask the engineer three things before anyone injects
- What is behind and under this wall: loose fill, sand or rock? Foam fills gaps in loose fill; it does not replace rock lost under the toe.
- Are the tie rods and deadman sound?
- Which openings are drains that must stay open?
Key Colony Beach’s building official has warned residents about firms selling “soil amendment” foam behind seawalls and under caps. Any such work that could affect a wall’s structure must be done by a Florida-licensed contractor registered with the city. KCB soil amendment warning
How does polyurethane seawall injection work?
The Army Corps grouting manual separates two jobs. Epoxy is often used to bond structural cracks, while urethane grouts mainly stop water or fill space. USACE EM 1110-2-3506
Polyurethane products differ. Some react with water and others mix two parts, and how much they expand depends on the formula and conditions. Bureau of Reclamation repair guide
- Void filling: filling a confirmed empty space in the soil behind the wall.
- Leak sealing: closing an open joint or crack that lets fill out, while leaving planned drains open.
- Soil stabilization: binding loose fill behind the wall. One manufacturer markets a single-part grout for this use behind seawalls; that is a product claim, not test data. [1]
Ask which of these goals the proposal names. A quote that says only “foam injection” leaves that open.
When does foam fit a seawall problem, and when does it not?
| Situation | Foam alone? | What else it needs |
|---|---|---|
Small void behind a sound wall, leak located | Often a fit | Seal the joint, then check the drains |
Sinkhole back after earlier fill or foam | Not alone | Find why it returned first |
Open joint between panels, sand leaking | Can help | Joint repair or new filter fabric may last longer |
Wall leaning, cap out of line | No | Tie rod, anchor or toe repair |
Cracked or spalling cap | No | |
Bottom scoured away at the base | No | Toe protection such as riprap |
Expanding foam pushes outward as it grows. Ask how the installer limits pressure against a weak panel.
What happens to foam near Keys waters?
The Florida Keys National Marine Sanctuary starts at the mean high-water mark, so the water face of most seawalls sits on its edge. 15 CFR 922.161 Injuring living or dead coral stays prohibited even where a seawall repair is allowed. 15 CFR 922.163
Products also behave differently in water. Bureau of Reclamation tests found polyurethane grouts performed differently underwater, and some formulas floated or clouded the water. USBR field research USBR underwater tests
- Which exact product will you use? Ask for the technical and safety data sheets.
- Is it meant for contact with salt water before it cures?
- What containment will be in the water, and what would make you stop?
Do I need a permit for seawall foam injection in the Keys?
Assume yes. Monroe County’s under-$7,500 exemption does not cover structural work or property in a flood hazard area. Monroe County exemption notice All of Marathon is mapped as coastal floodplain. Marathon floodplain page
| Where your lot is | Office and phone | What applies to foam work |
|---|---|---|
Unincorporated Monroe County | Building Department: Stock Island (305) 295-3990, Marathon (305) 289-2501 Monroe County Building, Stock Island Monroe County Building, Marathon | Online applications only. Residential work under $5,000 carries a flat $236 county fee. Monroe online permitting Res. 277-2025 |
City of Key West | Building Department (305) 809-3956 Key West Building Department | Permit for work over $1,000. Fee $36 per $1,000 of contract price, $100 minimum. Key West permits page Key West Code 14-2 |
City of Marathon | Building Department (305) 289-5052 Marathon Building Department | Seawall fee rate applies. Contractors must be licensed and registered with the city and the county. Marathon Res. 2025-73 Marathon Building FAQ |
Key Colony Beach | Building Department (305) 289-1212, ext. 3 Key Colony Beach Building Department | Every seawall repair needs a city permit, and foam firms must be licensed and registered with the city. KCB manual KCB warning |
City of Layton | City Hall (305) 664-4667 Layton City Hall | A contracted building code administrator reviews work; start with City Hall. Layton city staff |
If any work reaches the water side, state and sanctuary rules apply too. DEP’s Marathon office handles state review in Monroe County at (305) 289-7070. DEP Marathon office See the Key Colony Beach and Marathon guides for local detail, or the permit guide for every office.
What does seawall foam injection cost?
Foam is priced by material and labor, so quotes swing widely. Compare them line by line with the cost guide.
- Amount of resin included, and the price for each extra unit.
- Number of injection points, and how close they are to the house, pool or dock.
- Access from land or from a barge.
- Permit fees. Key West’s minimum is $100, Key Colony Beach charges a flat $100 up to $2,500 of work, and Monroe County charges $236 under $5,000. Key West Code 14-2 KCB Res. 2026-01 Res. 277-2025
The one public Keys example is a pier, not a house. Key West’s Navy Mole repair, with foam grout plus underwater welding, drew bids from $796,571 to $1,861,305. Key West ITB 26-002 The spread is the lesson: get at least three quotes on the same written scope.
What to ask a foam injection contractor before you sign
- What void or leak are you treating, and how did you find it?
- How much material is included, and what does each extra unit cost?
- If the void is bigger than expected, who approves the extra?
- What stays unrepaired: cap, panels, tie rods or toe?
- What does the warranty exclude? Does it cover a wall that moves?
- What is your Florida license category, and are you registered with the city or county issuing the permit? Check the record on MyFloridaLicense. DBPR license check
- If you want more than 10% up front: Florida law then requires the contractor to apply for permits within 30 days and start within 90 days after they issue. F.S. 489.126
What proof should I get after foam injection?
- A marked plan of every injection point.
- The product name and the amount used at each point.
- Before and after photos.
- Notes on drain checks and any foam that escaped.
- The final permit inspection.
- The warranty in writing.
If a sinkhole comes back, compare it to this record before you agree to inject again. It may point to a cause the first job missed.
Seawall foam injection questions
Is foam injection a permanent seawall fix?
It can last when the wall is sound and the leak is closed. If tie rods, joints or the toe keep failing, new voids will form. Ask what the warranty excludes before you rely on it.
Can foam stop my seawall from leaning?
No. Foam fills space; it does not replace the tie rods and deadman that hold a panel wall upright. KCB Seawall Owner’s Manual Read the tiebacks guide.
Who is allowed to do foam injection in the Keys?
Florida licenses marine specialty contractors for seawall and bulkhead work. Rule 61G4-15.100 Key Colony Beach requires a licensed contractor registered with the city for any foam work that could affect a wall. KCB warning
Show sourcesHide sources
Price and technical sources
- Prime Resins. Prime Flex 910 seawall repair example. Technical background. Source reviewed 2026-10-27
- Memorandum: File ID 26-5049 - Awarding the Re-Bid Navy Mole Pier Seawall Repair Project to Marino Construction Group, Inc. (ITB 26-002)Source reviewed 2026-10-28
- City of Key Colony Beach Seawall Owner's ManualSource reviewed 2026-10-28
- Regional Geologic Setting - Systematic Mapping of Bedrock and Habitats along the Florida Reef Tract (Professional Paper 1751)Source reviewed 2026-10-28
- Warning: Soil Amendment ServicesSource reviewed 2026-10-28
- EM 1110-2-3506, Grouting TechnologySource reviewed 2026-10-23
- Guide to Concrete Repair, Part ISource reviewed 2026-10-23
- 15 CFR 922.161 and Appendix I to Subpart P (Sanctuary boundary)Source reviewed 2026-10-28
- 15 CFR 922.163, Prohibited activities - Sanctuary-wideSource reviewed 2026-10-28
- Underwater Cure Polymeric Repairs to Seal Seepage Cracks, project 2398Source reviewed 2026-10-23
- Underwater Performance of a Hybrid Polymeric Repair Material to Seal Cracks in Concrete, DSO-2016-04Source reviewed 2026-10-23
- Building and Permitting (limited-work exemption notice)Source reviewed 2026-10-28
- FEMA Floodplain ManagementSource reviewed 2026-10-28
- Online Permitting ServicesSource reviewed 2026-10-28
- Resolution No. 277-2025 (Building Department permitting fee schedule)Source reviewed 2026-10-28
- Building Department - About UsSource reviewed 2026-10-28
- PermitsSource reviewed 2026-10-28
- Building Fees (Code Sec. 14-1 and 14-2)Source reviewed 2026-10-28
- BuildingSource reviewed 2026-10-28
- Resolution 2025-73, Exhibit A Permit Fee ScheduleSource reviewed 2026-10-28
- Building Frequently Asked QuestionsSource reviewed 2026-10-28
- Building Department and Code EnforcementSource reviewed 2026-10-28
- Contact UsSource reviewed 2026-10-28
- City StaffSource reviewed 2026-10-28
- SED Marathon OfficeSource reviewed 2026-10-28
- Resolution No. 2026-01 (Fee Schedule for Building Department Permits and Services)Source reviewed 2026-10-28
- Florida DBPR construction business verificationSource reviewed 2026-10-27
- Section 489.126, Florida Statutes: Moneys received by contractorsSource reviewed 2026-10-28
- Rule 61G4-15.100, Certified Specialty Contractors (final rule text, effective 8/28/2024)Source reviewed 2026-10-28