Direct Answer
Voids behind seawalls happen when soil is lost from behind the wall and empty space forms below the surface. In Florida, this usually occurs when water carries soil through seawall joints, cracks, panel gaps, failed filter fabric, failed black filter fabric, failed drains, missing or clogged weep holes, or other weak points in the seawall system.
Homeowners may describe these areas as holes, sinkholes, soft spots, washouts, depressions, or voids behind the seawall. In many cases, they are not true geological sinkholes. They are erosion voids caused by soil escaping from behind the wall.
A void behind a seawall should not be repaired by simply filling the hole with dirt, sand, shell, or gravel. That may cover the surface temporarily, but it does not stop the soil from escaping. The right repair should identify where the soil is going, reduce the erosion pathway, fill the void, stabilize the surrounding soils, and improve pressure relief when needed.
A void behind a seawall means the soil has already lost support in that area. The visible hole or depression is not the real problem. It is the surface sign that soil has moved, washed out, or escaped through the seawall system.
What Is a Void Behind a Seawall?
A void behind a seawall is an empty space where soil or backfill used to be. The surface may show a hole, depression, soft area, settled pavers, sinking concrete, or a low spot near the seawall cap.
Voids can form directly behind the wall, under pavers, beneath patios, below pool decks, near walkways, around landscaping, or behind seawall caps.
Homeowners may notice:
- A hole behind the seawall
- A soft spot near the seawall cap
- A depression in the yard
- Pavers sinking along the wall
- Concrete settling near the seawall
- A patio or pool deck dropping near the wall
- Soil or sand mounds on the water side of the seawall
- The same hole returning after being filled
- Water flowing through joints or cracks
- Gaps between seawall panels
- Landscaping sinking or pulling away near the wall
The surface opening may be small, but the void below can be larger than it looks. That is why repeated filling without inspection can hide the problem instead of solving it.
If you are seeing voids, soft spots, or holes behind a seawall, the issue should be evaluated before nearby pavers, concrete, patios, pool decks, or structures begin to settle.
Read more: Signs Your Seawall Is Failing in Florida
Why Voids Behind Seawalls Happen
Voids behind seawalls form when soil leaves the area behind the wall.
In most cases, water is the force moving the soil. Water finds a weak point in the seawall system, carries soil with it, and leaves empty space behind the wall.
Common causes include:
- Open seawall panel joints
- Cracks in the wall
- Gaps beneath or around panels
- Failed filter fabric
- Failed black filter fabric
- Black filter fabric torn during construction
- Failed or missing weep hole filters
- Clogged weep holes or drains
- Poor pressure relief behind the wall
- Heavy rain pushing water toward the seawall
- Poor drainage behind the wall
- Storm surge
- High tides
- Boat wakes
- Wave action
- Loose sandy backfill
- Wall movement creating new gaps or cracks
The exact cause matters because the repair should not only fill the void. It should also address the pathway that allowed soil to escape.
For a deeper explanation of soil-loss causes, see: What Causes Soil Loss Behind Seawalls?
Why Voids Are More Than a Surface Hole
A void behind a seawall is not just a cosmetic problem.
The visible hole, depression, or soft spot is a sign that support below the surface has been lost. If the soil continues escaping, the affected area can expand.
Voids can lead to:
- Larger holes behind the seawall
- Settled pavers along the wall
- Sinking concrete
- Patio settlement
- Pool deck settlement
- Walkway settlement
- Landscaping damage
- Soil loss near structures
- Increased water movement behind the wall
- More pressure on the seawall
- Larger repair costs later
A small hole near the cap may seem minor, but if it keeps returning, it usually means soil is still moving. The question is not only how to fill the hole. The question is why the hole formed and whether the soil is still escaping.
This is especially important when the seawall is close to a pool, patio, lanai, deck, walkway, driveway, or house. Those improvements rely on the soil behind the seawall for support.
Void, Sinkhole, Soft Spot, or Washout?
Homeowners use different words to describe voids behind seawalls.
Common descriptions include:
- “There is a sinkhole behind my seawall.”
- “There is a hole by the seawall.”
- “The ground feels soft near the seawall.”
- “My pavers are sinking by the seawall.”
- “The dirt keeps disappearing.”
- “There is a depression behind the seawall.”
- “The same hole keeps coming back.”
- “The seawall is washing out.”
These terms are understandable, but they do not always mean the same thing technically.
Many holes behind seawalls are not true geological sinkholes. They are usually erosion voids, washouts, or depressions caused by soil loss behind the wall. The soil may be escaping through joints, cracks, failed filters, weep holes, drains, or other weak points.
That distinction matters because a geological sinkhole and a seawall erosion void are different problems. The right seawall void repair should focus on where the soil is escaping, how water is moving, whether pressure relief is working, and whether the wall is still serviceable.
Early Voids vs Urgent Seawall Warning Signs
| What You Notice | What It May Mean | Level of Concern |
| Small hole behind seawall | Early soil loss or erosion pathway | Should be inspected if recurring |
| Soft spot along wall | Hidden void below surface | Concerning if spreading |
| Depression near cap | Soil loss beneath surface | Should be evaluated |
| Same hole returns after filling | Active soil escape pathway | High concern |
| Pavers settling near wall | Soil support has been lost | Concerning |
| Concrete or pool deck sinking near wall | Voids or soil loss beneath slab | High concern |
| Sand mound on water side | Soil escaping through wall | Strong sign of active soil loss |
| Water flowing through joints | Drainage or joint issue | Concerning |
| Gaps between panels | Soil loss pathway | Should be evaluated |
| Wall leaning or bowing | Structural wall movement | Urgent |
| Cracks with exposed rebar or spalling | Structural deterioration | Urgent |
| Tieback, deadman, or anchor concern | Possible structural issue | Urgent |
This table is a guide, not a diagnosis. A small surface hole may not mean the wall is failing structurally, but recurring voids, soft spots, soil mounds on the water side, and settlement near the wall should not be ignored.
Checklist: Signs a Void Behind a Seawall Should Be Inspected
A void behind a seawall should be inspected if you notice:
- A hole behind the seawall
- A depression near the seawall cap
- A soft spot along the land side of the wall
- A void that keeps returning after being filled
- Soil disappearing behind the wall
- Pavers settling or separating near the seawall
- Concrete sinking near the wall
- A pool deck or patio dropping near the seawall
- Walkways settling near the wall
- Landscaping sinking or pulling away
- Soil or sand mounds on the water side of the wall
- Water flowing through wall joints, cracks, or openings
- Gaps between seawall panels
- Failed or exposed filter fabric
- Failed black filter fabric
- Cracks in the seawall cap or panels
- Wall leaning, bowing, or rotating
- A seawall located close to a pool, patio, deck, house, or structure
If a void is near a pool deck, patio, walkway, or structure, it should be evaluated sooner because soil loss can affect the improvements behind the wall.
Why Filling the Hole Does Not Fix the Void
Filling a hole behind a seawall with dirt, sand, shell, gravel, or concrete may make the surface look better temporarily, but it usually does not fix the problem.
The reason is simple: the hole is not the cause. The hole is the result.
If soil escaped through a joint, crack, failed filter, failed black filter fabric, drain, or pressure-related weak point, new fill can wash out the same way.
This is why many homeowners keep filling the same hole over and over.
Filling the hole without stopping the soil loss pathway can lead to:
- Recurring holes
- Larger voids below the surface
- Settled pavers
- Sinking concrete
- Pool deck settlement
- Patio or walkway settlement
- Continued soil loss into the water
- Higher repair costs later
If the same hole keeps coming back, the problem is not that you need more fill material. The problem is that soil is still escaping.
Why Voids Often Form Near Pavers, Pool Decks, Patios, and Walkways
Voids behind seawalls often show up where homeowners have hardscape or outdoor living areas close to the wall.
Common areas include:
- Pavers along the seawall cap
- Pool decks near the wall
- Concrete patios
- Lanais
- Walkways
- Landscape beds
- Seawall caps
- Outdoor kitchens or seating areas
- Waterfront decks or dock access areas
These areas are vulnerable because they depend on stable soil support. When soil is lost behind the seawall, the surface above can settle.
Pavers may dip or spread. Concrete may crack or sink. Pool decks may slope or separate. Walkways may become uneven. Landscaping may drop or pull away.
In some cases, homeowners first notice the issue because the pavers or concrete settle before they notice the actual void.
If a pool deck is settling near the seawall, the problem may involve both seawall soil loss and slab support loss.
Read more: Pool Deck Sinking Near Coping: Causes and Repair Options
If concrete near the seawall is hollow or settling, void filling and slab support may also need to be evaluated.
Read more: Voids Under Concrete Slabs: What Causes Them and How to Fix Them
What Sand or Soil Mounds on the Water Side Mean
Sand or soil mounds on the water side of a seawall are one of the strongest signs of active soil loss.
A void behind the wall shows that soil is missing. A mound on the water side may show where that soil is going.
These mounds may appear:
- At panel joints
- Near cracks
- Below gaps in the wall
- Near failed drains or weep holes
- Along the bottom of seawall panels
- After heavy rain
- After high tides or storm surge
- After repeated boat wakes or wave action
If soil or sand is collecting on the water side of the wall, the seawall may be allowing backfill to escape. That means the void behind the wall may continue growing until the escape pathway is addressed.
This is why Helicon looks at both the land side and water side of the seawall during an evaluation.
How Water Pressure Makes Voids Worse
Water pressure can make voids behind seawalls worse.
When water builds up behind the wall and cannot escape properly, it creates pressure. Water is powerful, and it will find a place to release. If the wall has weak points, water may move through them and carry soil with it.
Weak points may include:
- Open joints
- Cracks
- Gaps between panels
- Failed drains
- Clogged weep holes
- Torn black filter fabric
- Failed filter fabric
- Deteriorated wall sections
- Construction defects
If water exits through an unfiltered opening, soil can escape with it. If water cannot exit at all, pressure can build behind the wall and stress the structure.
That pressure can contribute to cracking, bowing, leaning, rotating panels, exposed reinforcement, spalling, and, in severe cases, wall failure.
A good seawall void repair plan should consider pressure relief, not just soil filling.
Read more: Jet Filter Pressure Relief System
How Helicon Evaluates Voids Behind Seawalls
When Helicon evaluates voids behind seawalls, the goal is to determine why the void formed, whether soil is still escaping, whether pressure relief is working, and whether the seawall is still serviceable.
A proper evaluation may include:
- Looking for voids, holes, depressions, and soft spots
- Checking whether the same hole has returned after filling
- Inspecting pavers, concrete, pool decks, patios, walkways, and landscaping near the wall
- Looking for soil or sand mounds on the water side
- Checking panel joints, cracks, and gaps
- Reviewing water movement through the wall
- Looking for failed or exposed filter fabric
- Looking for signs of failed black filter fabric
- Reviewing weep holes, drains, and pressure relief
- Checking the seawall cap for cracks or movement
- Looking for leaning, bowing, or rotating panels
- Using a soil probe behind the wall where appropriate
- Determining whether nearby improvements are at risk
- Determining whether the issue appears soil-related, pressure-related, structural, or a combination
The inspection should answer several key questions:
- How large is the voided or softened area?
- Is soil still escaping?
- Where is the soil likely going?
- Is water pressure contributing?
- Is the wall still serviceable?
- Are nearby pavers, concrete, pool decks, patios, or structures affected?
- Is the best repair void filling, soil stabilization, pressure relief, structural evaluation, replacement, or a combination?
The right repair starts with understanding the cause of the void.
How to Fix Voids Behind Seawalls
The right way to fix voids behind seawalls depends on the cause, wall condition, access, soil loss, pressure relief, and whether the wall is structurally serviceable.
Common repair options may include:
- Seawall inspection
- Soil probing behind the wall
- Identifying where soil is escaping
- Polyurethane seawall soil stabilization
- Permeation grouting behind the seawall
- Void filling behind the wall
- Erosion pathway reduction where appropriate
- Targeted joint sealing where appropriate
- Jet Filter pressure relief system when viable
- Well Points when Jet Filters are not viable
- Drainage and pressure relief improvements
- Structural engineer or marine contractor evaluation when needed
- Seawall replacement when the wall is beyond repair
For many Helicon seawall projects, the goal is to fill voids, stabilize the soils behind the wall, reduce continued soil loss, and improve pressure relief. Jet Filters are commonly installed when viable. Well Points may be used when Jet Filters are not a viable installation option.
The repair should match the condition of the wall. A serviceable wall with soil loss behind it may be a strong candidate for void filling, soil stabilization, erosion pathway reduction, and pressure relief. A wall that is leaning severely, bowing, rotating, structurally deteriorated, or beyond repair may require structural evaluation or replacement.
Read more: Seawall Soil Stabilization
Seawall Void Filling vs Seawall Replacement
Voids behind a seawall do not automatically mean the wall needs to be replaced.
In many cases, the seawall may still be serviceable, but the soils behind it are being lost. In that situation, seawall erosion repair may be appropriate.
Seawall erosion repair may include:
- Filling voids behind the wall
- Stabilizing loose or weakened soils
- Reducing continued soil loss
- Improving pressure relief
- Protecting nearby improvements
Seawall replacement may be needed when:
- The wall is leaning severely
- Panels are bowing or rotating
- The cap or panels are severely cracked
- Structural steel is exposed and deteriorating
- Spalling or concrete deterioration is advanced
- Tiebacks, deadmen, or anchors are failing
- The wall is no longer serviceable
- Engineering determines replacement is needed
Helicon’s focus is not replacing every seawall. Helicon’s seawall erosion repair focuses on stabilizing soil behind serviceable walls, filling voids, reducing continued soil loss, and improving pressure relief.
Read more: Seawall Erosion Repair
If the wall itself is structurally failing, replacement or structural engineering may be needed.
Read more: Seawall Repair vs Replacement
How Much Does It Cost to Fix Voids Behind a Seawall?
The cost to fix voids behind a seawall depends on wall length, void size, soil loss, access, wall condition, depth, drainage, pressure relief needs, nearby structures, and whether the wall is still serviceable.
Typical ranges may include:
- Seawall inspection: free when within Helicon’s service area
- Smaller seawall soil stabilization or void-filling projects: often around $5,000 to $15,000
- Larger seawall stabilization or void-filling projects: often around $15,000 to $40,000
- Seawall replacement: often around $800 to $1,500 per linear foot for vinyl, steel sheet, or concrete panel seawalls, depending on wall type, access, permitting, engineering, depth, site conditions, and waterfront conditions
*These are typical Florida pricing examples based on published industry resources and contractor pricing guides. They are intended for educational purposes only and are not Helicon’s pricing. Every home is different, and a professional inspection is the only way to determine the appropriate repair and provide an accurate quote.
Void filling and full seawall replacement are very different repairs. Void filling and stabilization are often focused on soil loss behind a serviceable wall. Replacement involves removing and rebuilding the wall system and is typically much more expensive.
The right repair should be based on the cause of the void, the condition of the wall, and the risk to nearby improvements.
What Homeowners Should Not Do
The biggest mistake homeowners make is filling the visible hole without stopping the soil loss.
Homeowners should avoid:
- Filling voids with dirt, sand, shell, or gravel without fixing the escape pathway
- Ignoring soft spots because the wall still looks upright
- Assuming every void behind a seawall is a geological sinkhole
- Resetting pavers before stabilizing the soils below
- Replacing concrete or pool deck areas before fixing soil loss
- Ignoring soil or sand mounds on the water side
- Ignoring pressure relief, clogged drains, or failed weep holes
- Waiting until the wall leans, bows, or cracks severely
- Assuming every void means full seawall replacement is required
When to Schedule a Seawall Void Inspection
You should schedule a seawall void inspection if you notice holes, soft spots, depressions, settled pavers, sinking concrete, or recurring washouts behind the wall.
Call an expert if you notice:
- A hole behind the seawall
- A depression near the cap
- A soft spot along the wall
- A void that keeps returning after being filled
- Soil disappearing behind the wall
- Pavers settling near the seawall
- Concrete sinking near the wall
- Pool deck or patio settlement near the seawall
- Soil or sand mounds on the water side
- Water flowing through joints, cracks, or panel openings
- Failed or exposed filter fabric
- Failed black filter fabric
- Cracks in the cap or panels
- Wall leaning, bowing, or rotating
- A seawall near a pool, patio, deck, house, walkway, or structure
Not sure if the hole behind your seawall is minor, active, or urgent? Helicon can evaluate the wall, soil loss, voids, pressure relief, drainage, nearby improvements, and structural warning signs to help determine the right next step.
Why Florida Homeowners Trust Helicon
Helicon has been helping Florida homeowners solve seawall erosion repair, soil stabilization, foundation repair, concrete lifting, sinkhole repair, pool deck settlement, sidewalk settlement, driveway settlement, void filling, and slab support problems since 2004.
As a family-owned Florida company, Helicon understands the soil conditions, water movement, storm exposure, drainage issues, wall systems, filter failures, pressure problems, and settlement patterns that affect waterfront properties across Tampa Bay, Orlando, Southwest Florida, and surrounding areas.
We are not there to tell every homeowner that every void means seawall replacement. We are also not there to ignore structural wall movement when replacement or engineering may be needed. We are there to determine whether the void is caused by soil loss, pressure, drainage, failed filtration, structural wall movement, or a combination.
Sometimes the wall is still serviceable, but the soil behind it is being lost. Sometimes a void needs to be filled. Sometimes the surrounding soils need stabilization. Sometimes pressure relief needs to be improved. Sometimes the wall is structurally compromised and replacement needs to be evaluated.
The goal is always the same: identify the cause, protect the property, and recommend the least invasive repair that provides a long-term solution.
Schedule a Free Seawall Void Inspection
If you see holes, voids, soft spots, depressions, settled pavers, sinking concrete, or sand mounds on the water side of your seawall, Helicon can help.
Our team can evaluate the seawall, soil loss, voids, drainage, pressure relief, filtration concerns, nearby improvements, and structural warning signs when needed to help determine whether the problem is soil-related, pressure-related, structural, or a combination.
Schedule a free seawall void inspection with Helicon to find out what is causing the issue and what should be done next.
FAQ
What causes voids behind seawalls?
Voids behind seawalls are usually caused by soil loss. Water carries soil through open joints, cracks, panel gaps, failed filter fabric, failed black filter fabric, failed weep holes, drains, or other weak points in the seawall system.
Are voids behind seawalls the same as sinkholes?
Usually not. Homeowners may call them sinkholes, but many voids behind seawalls are erosion voids caused by soil escaping through the seawall system. They are not typically true geological sinkholes.
Why does the same hole behind my seawall keep coming back?
The hole keeps coming back because soil is still escaping. Filling the hole replaces missing material temporarily, but it does not stop the joint, crack, failed filter, drain issue, or pressure problem that is allowing soil to wash out.
Can I just fill the void with dirt, sand, shell, or gravel?
Filling the void may hide the surface opening temporarily, but it usually does not solve the problem. If the soil escape pathway remains open, the new fill can wash out again.
What do sand mounds on the water side of a seawall mean?
Sand or soil mounds on the water side often mean backfill is escaping through the seawall. This is one of the strongest signs of active soil loss behind the wall.
Can voids behind a seawall damage my pool deck or patio?
Yes. Voids behind seawalls can remove support beneath pavers, pool decks, patios, walkways, landscaping, and other improvements near the wall. If the soil continues moving, those surfaces may settle or crack.
How do you fix voids behind seawalls?
The repair may include void filling, polyurethane seawall soil stabilization, permeation grouting, erosion pathway reduction, Jet Filters when viable, Well Points when Jet Filters are not viable, drainage improvements, or structural evaluation if the wall is moving or deteriorated.
Do voids behind seawalls always mean replacement is needed?
No. If the wall is still serviceable, void filling, soil stabilization, erosion reduction, and pressure relief may be appropriate. If the wall is leaning severely, bowing, rotating, structurally deteriorated, or beyond repair, replacement may be needed.
How much does it cost to fix voids behind seawalls?
Smaller seawall void filling or soil stabilization projects often range from around $5,000 to $15,000. Larger seawall stabilization or void filling projects often range from around $15,000 to $40,000. Full seawall replacement often ranges from around $800 to $1,500 per linear foot.
When should I call Helicon about voids behind my seawall?
Call Helicon if you notice holes, voids, soft spots, depressions, recurring washouts, settled pavers, sinking concrete, sand mounds on the water side, water flowing through joints, failed filter fabric, poor drainage, or signs that the wall is leaning, bowing, or rotating.
