Void Filling Under Concrete in Illinois: What It Is, Why It Happens, and How to Fix It
When concrete starts sinking, separating from steps, or forming gaps underneath, the cause is almost always the same: a void forming under the slab. In Illinois, voids are extremely common due to weather, drainage patterns, and natural soil movement.
Void filling is one of the most effective ways to restore support, stop sinking, and extend the life of your concrete—without tearing out and replacing your slab. In this guide, we’ll explain what causes voids, the signs to look for, and how Scritchlow Concrete Lifting and Slab Jacking fixes them for homeowners across Central Illinois.
What Is Void Filling?
Void filling is the process of injecting specialized material beneath a concrete slab to fill empty pockets caused by erosion, washout, or soil settlement. Once the void is filled, the slab regains proper support and can often be lifted back to its original level.
It’s one of the fastest, most efficient ways to stop sinking slabs and prevent further damage.
Why Do Voids Form Under Concrete in Illinois?
Illinois weather and soil conditions naturally contribute to void formation. Over time, the ground shifts, washes out, or settles—creating hollow spaces where concrete eventually sinks.
Here are the most common causes:
1. Water Washout
Heavy rain, downspouts, or improper drainage can wash soil away from under the slab. Once the soil disappears, nothing is left to support the concrete.
2. Freeze–Thaw Cycles
Illinois winters take a toll on concrete. As moisture freezes and expands, then thaws and contracts, it weakens soil and creates shifting voids.
3. Poor Soil Compaction During Construction
If the soil beneath your driveway, sidewalk, or porch wasn’t compacted properly when the home was built, it will continue settling for years.
4. Burrowing Animals
Groundhogs, chipmunks, and other small animals love tunneling under concrete slabs, creating pockets that later collapse.
5. Long-Term Soil Settlement
All soil settles eventually. Some areas settle faster than others, especially where the soil is loose or was disturbed during construction.
When these issues occur, the concrete above begins to drop—sometimes slowly over years, sometimes seemingly overnight.
Common Signs You Have a Void Under Your Concrete
Most homeowners don’t realize erosion is happening until the concrete starts showing symptoms. Here are the signs to watch for:
✔ A visible gap under the slab
✔ The slab sounds hollow when tapped
✔ Cracks forming or widening
✔ Concrete pulling away from steps or foundations
✔ Water flowing under or pooling around the slab
✔ A sinking, uneven, or rocking section of concrete
✔ Burrowing animals accessing the space below
If you notice any of these, void filling is likely needed. Voids only get bigger over time.
How Scritchlow Performs Void Filling
Our process is designed to restore stability quickly, cleanly, and safely. Here’s how it works:
1. Inspection & Void Detection
We begin by evaluating the slab, the soil beneath it, and the surrounding drainage. This allows us to pinpoint the cause of the void and determine the best repair method.
2. Drill Small Injection Holes
We drill small holes—typically about the size of a quarter—into the slab. These holes act as access points to reach the void underneath.
3. Inject Grout to Fill the Void
A specialized grout mixture is pumped beneath the concrete. This material flows into empty spaces, stabilizes loose soil, and completely fills the void.
4. Lift the Slab (If Needed)
Once the void is filled, we gently lift the concrete back into position. This eliminates trip hazards and restores proper grading for water drainage.
5. Patch & Clean
After the repair, we patch the small holes and clean the area. Most repairs are completed in just a few hours, and the concrete is usually ready for use the same day.
Pressure Grouting & Compaction Grouting
Some situations require an advanced repair method known as pressure grouting or compaction grouting.
These techniques are ideal when:
- The soil is extremely loose
- Voids are deep or widespread
- The slab supports extra weight (garage floors, commercial areas)
- There is structural settlement beneath the slab
Compaction grouting strengthens the soil by injecting grout in a controlled way that compresses and densifies the surrounding soil, increasing its load-bearing capacity.
Our team determines the right solution during the inspection.
Void Filling vs Concrete Replacement
Many homeowners assume sinking concrete must be replaced—but in most cases, it doesn’t.
Void filling:
- Preserves your existing concrete
- Restores support under the slab
- Prevents further sinking
- Fixes drainage issues
- Takes only a few hours
- Costs significantly less than replacement
- Doesn’t disturb your yard or landscaping
Replacement is usually only needed if the slab is severely broken.
Where We Commonly See Voids Form
We frequently repair erosion and voids under:
- Driveways
- Sidewalks
- Patios
- Porches and stoops
- Steps
- Garage floors
- Pool decks
- Basement slabs
If you notice sinking or gaps in any of these areas, void filling is likely the right solution.
Why Illinois Homeowners Choose Scritchlow
Scritchlow Concrete Lifting and Slab Jacking has helped homeowners across Central Illinois stabilize their concrete for decades. Customers choose us because:
- We’re a trusted, locally owned company
- We specialize exclusively in concrete lifting & void repair
- Our methods are clean, efficient, and long-lasting
- We fix the cause of the problem—not the symptom
- We provide honest recommendations based on real inspection results
Your concrete deserves the right fix the first time.
When to Call a Professional
You should schedule an inspection if:
- The slab is visibly sinking
- Gaps beneath the slab keep growing
- New cracks are forming
- Water drains toward or under the concrete
- You hear a hollow sound when stepping on the slab
- Erosion is visible after rainfall
Voids always expand with time. The longer the wait, the worse the damage—and the repair cost—can become.
Get a Free Void Filling Evaluation
Scritchlow Concrete Lifting and Slab Jacking proudly serves:
Bloomington, Normal, Peoria, Champaign, Decatur, Lincoln, Springfield, and surrounding Illinois communities.
If you’re noticing sinking slabs, gaps, or erosion under your concrete:
👉 Call us now at 877-287-0402
👉 Or request a free inspection on our website
We’ll evaluate your concrete, identify the root problem, and provide the right repair—quickly, safely, and affordably.