Expansive soils are a hidden menace across the country when it comes to causing damage to homes’ foundations. Whether you live on the dunes of Long Island, in a brownstone in Brooklyn or on a ranch in the Midwest, clay-rich expansive soil doesn’t care about your ZIP code. When it gets wet, it swells; when it dries, it shrinks. That’s just a natural fact.
The constant push-and-pull of this natural occurrence stresses foundations, leaving homeowners with cracked walls, sticking doors and sloping floors. We see this every day in the field; a lot of the homes in Long Island and Brooklyn built on clay can suffer just as much as those in Texas or Colorado. We see this every day in the field as contractors, especially in areas like Massapequa, East Islip, Northport, Port Jefferson, and Bay Shore. Parts of Brooklyn like Red Hook and Bay Ridge are also built on clay-heavy oils that can swell and shrink with moisture.
These homes can suffer just as much as those in Texas or Colorado when it comes to foundation movement and damage; it just depends on where you live and how much water the soil is exposed to.
That said, we are writing this blog to help you understand what expansive soils are, why they’re so destructive, how to spot the warning signs, and what you can do to protect your home. With more than three decades of experience stabilizing foundations and repairing damage from shrink–swell cycles, we’ve compiled clear advice and actionable steps on this page to keep your property safe no matter where you live.
What Is Expansive Clay Soil and Why It Undermines Homes
Expansive clay soil isn’t just dirt it’s a dynamic, shape-shifting material that can quietly wreak havoc on your foundation. The trouble starts when moisture levels in the soil change. Clay-heavy soils, particularly those containing smectite or montmorillonite act like sponges, swelling significantly when wet and shrinking when dry.
This process creates gaps and uneven support under your home. Those gaps can stress on your foundation, causing gradual, often unnoticed damage until cracks, sloping floors, or stuck doors appear.
Why Montmorillonite Matters
Here’s the thing: It comes down to mineral makeup. 2:1 clays like montmorillonite (mont-muh-RIL-uh-nite), named for its layered crystal structure, can bulge up to 15 times their dry volume when fully saturated.
The problem is, when the ground bulges like that next to your foundation, it’s not just movement. It’s putting lateral pressure on your foundation, and that’s what causes damage.
Even worse?
Seasonal shifts mean this cycle happens over and over, pretty much every day. Think of it like a never-ending hamster wheel for your foundation: rain comes, the soil swells. Summer hits, it shrinks. Your foundation just tries to hang on…but it can’t. It’s flat, not meant to move much, and it’s got a lot of weight on it.
Now, how do you know if your home, building, or new home is on expansive soils? Check this out…
How Do You Know if You Have Expansive Clay Soils?
By now, you understand how clay soils across Long Island and beyond shrink and swell the ground with every change in moisture. And here’s something else: you can’t always see expansive soils just by looking at the dirt in your yard. Especially in Long Island where we live and operate.
The process is the same no matter whether you’re in Queens or the Hamptons, Denver or Dallas, the process is the same: we measure how soil reacts to moisture using the methods below to connect the dots between invisible soil behavior and very real damage inside your house.
Here are some of the methods used to test your soil for how active it is:
- Plasticity Index Test: The plasticity index test measures the soil’s ability to retain and release moisture, helping to determine its swelling potential.
- Swell Potential Test: The swell potential test evaluates how much the soil expands when saturated with water, (as discussed above) indicating its activity level.
- Moisture Content Analysis: A moisture content analysis determines the current moisture levels in the soil and its capacity to shrink or swell with changes in water content.
- Drainage Characteristics Test: The drainage characteristics test assesses how well the soil drains water, which affects its overall stability and movement.
Risks Homeowners Face with Expansive Soil Near Their Homes
Expansive soil doesn’t show up like a hurricane or a wildfire but it’s just as destructive over time. It works slowly, shifting the ground beneath your home little by little. But once the signs appear, you’re already dealing with costly consequences.
Foundation Damage That Hits Home
Zavza Seal sees this across the tri-state area, especially in homes built on problematic soils in Massapequa, East Islip, Northport, Port Jefferson, Bay Shore, and parts of Brooklyn like Red Hook and Bay Ridge. It doesn’t matter how strong the concrete is, if the soil moves, the house does too.
Painful Red Flags to Watch For:
- Cracked Foundations Or Drywall: Visible foundation cracks near windows or door frames, often indicating foundation movement or structural stress.
- Sticking Doors And Windows: Difficulty opening or closing doors and windows, suggesting warped framing from foundation issues.
- Sloping Or Uneven Floors: Noticeable tilting or sinking of floors, caused by foundation settling or upheaval.
- Bowed Basement Walls: Bowing walls curve inward due to lateral pressure from surrounding soil.
- Moisture Intrusion And Mold: Moisture intrusion starts when water seeps through cracks in your foundation. Left unnoticed or unrepaired, the excess moisture can lead to mold growth.
- Crumbling Driveways Or Patios: Concrete surfaces breaking apart due to soil heaving, settling, or erosion.
The Financial Impact
Expansive soils cause more property damage in the U.S. annually than earthquakes, floods, and hurricanes combined. According to the American Society of Civil Engineers, the tab runs into the billions each year.
- ASCE: Expansive soils inflict over $2.3 billion in annual damage, topping disasters
- Suffolk County: Expansive soils exert up to 14,000 lb/ft; special foundations required
- Building Codes: Suffolk County requires special design when Expansion Index exceeds 20
- Research: Some studies estimate U.S. expansive‑soil losses exceed $9 billion annually.
Foundation Design Options
- Deep Supports: For expansive soils, drilled piers or helical piles extend into stable ground, providing a secure foundation.
- Mat Foundations: A raft-style foundation spreads weight evenly across a wide area, reducing the impact of soil shifts.
- Post‑tensioned Slabs: Slabs reinforced with tensioned cables counteract soil movement by holding the concrete in compression.
These are proven engineering solutions—not gimmicks—widely used in regions such as Texas and Colorado, and increasingly suitable for certain Long Island conditions.
Chemical Stabilization (When Needed)
Sometimes the best long‑term fix is improving the soil itself:
- Lime or Cement Treatment: Adding lime or cement reduces plasticity and lowers moisture absorption in problem soils.
- Fly Ash Amendments: Incorporating fly ash helps bind particles and make the soil denser.
These treatments must be designed and tested by qualified professionals, but when properly applied, they permanently reduce the soil’s shrink‑swell potential.
Local Story: Why Expansive Clay Soil Hits Long Island Particularly Hard
Long Island’s landscape is built on a complex mix of Cretaceous sands, gravels, and clays capped with Pleistocene glacial deposits. Beneath our beaches and backyards are pockets of low-permeability clay that behave like sponges swelling dramatically in wet weather and shrinking when conditions dry out. Add Long Island’s wet springs and hot, often-dry summers, and you get repetitive stress cycles on foundations.
While Suffolk County overall is considered low-risk for expansive soil, certain areas—including parts of Smithtown have moderate swelling potential. Towns such as Massapequa, East Islip, Northport, Port Jefferson, and Bay Shore are built on or near these clay layers and glacial tills. Plus, fluctuating groundwater from the upper glacial aquifer can saturate these soils, causing even more movement. So yes, expansive soil isn’t only a problem out West. It’s right here in our neighborhoods, and ignoring it won’t make it go away.
What to Do If You’re Already Seeing Cracks and Movement
If you’ve already noticed cracks in your walls, sticking doors, or uneven floors, don’t panic—but don’t ignore it either. Here’s a step-by-step plan to keep damage from getting worse:
1. Observe and Record
Take clear photos of cracks, gaps, or sloping areas and note the dates. Tracking these changes over time helps determine whether the problem is active or stable.
2. Manage Moisture First
Address water issues right away. Clean gutters, extend downspouts, regrade soil, and fix leaks. Keeping soil moisture consistent is often the fastest way to stop movement.
3. Reinforce the Foundation
If problems persist, bring in a foundation professional. Solutions may include piers, underpinning, void forms, or reinforced slabs—tailored to your soil and structure.
4. Schedule Regular Check-Ins
Even after repairs, make foundation health part of your annual routine. Seasonal inspections help you catch small shifts before they lead to costly damage.
What Expansive Clay Soil Means for Your Foundation: Final Thoughts
Expansive soil damage is insidious. It doesn’t arrive with the drama of a hurricane, but it can be just as devastating. Clay soils can expand by ten percent or more, exerting enough force to crack foundations and warp entire structures. Nationally, more than a quarter of homes experience some damage from swelling soils, and the annual price tag runs into the billions.
The good news? With the right strategies consistent moisture management, timely repairs, and, when needed, engineered solutions this damage is preventable. Early action saves money and stress. If you see doors that suddenly won’t close, or notice cracks growing wider during dry spells, don’t wait. Zavza Seal specializes in soil testing and tailored foundation solutions for Long Island conditions. We’ll give you a clear plan so you can fix the problem once, avoid repeat repairs, and sleep better at night.
Got Existing Damages? Contact Zavza Seal Today for a Free Expert Opinion!
