When concrete loses support from below, the problem usually starts with hidden empty spaces, weak soils, or both. Our concrete void filling and soil stabilization process uses polyurethane foam injection to fill underground voids, compact loose soils and base materials, and help restore more reliable support beneath your slab.
What Is Concrete Void Filling?
Concrete void filling is the process of filling empty gaps and airspaces beneath a concrete slab that have formed over time. Those voids often develop when soil washes away, settles unevenly, shrinks, or breaks down, leaving the slab partially unsupported from below.
What Is Soil Stabilization?
Soil stabilization and concrete slab stabilization mean essentially the same thing because the goal is the same: strengthen support beneath the concrete. While concrete void filling can sometimes be done with materials that simply occupy space, polyurethane foam can do more than fill a gap by also helping stabilize the surrounding support zone.
How Concrete Void Filling & Soil Stabilization Work Together
In many cases, concrete void filling and soil stabilization are part of the same repair. If voids are present beneath a concrete slab and the surrounding soils are loose or weakened, filling the void alone may not fully address the support problem unless the injected product also helps stabilize the surrounding base.
That is where polyurethane foam stands out. As it expands, it flows into the voids and compacts loose soils, while forming a rigid, lightweight mass that improves support under the slab. In that sense, polyurethane-based concrete void filling can also serve as soil stabilization when the application technique and products are right.
Signs You May Have Voids or Weak Soil Beneath Your Concrete
A slab does not need to be badly broken before support loss becomes a problem. Early warning signs often show up long before full failure, especially when concrete void filling or soil stabilization would still be a practical repair option.
Common Causes of Voids Beneath Concrete
- Poor drainage, runoff, plumbing leaks, and groundwater movement, which can wash away fine soils beneath the slab.
- Poor compaction during construction, which allows the subgrade to settle and create unsupported pockets over time.
- Freeze-thaw cycles and shrinking soils, which can shift the ground and leave gaps below the concrete.
- Buried organic material or root activity, which can break down or disturb the base beneath the slab.
- Burrowing animals such as rodents, rabbits, skunks, and other small mammals can dig beneath concrete, disturb the supporting soil, and create channels for water and further erosion.
Common Void Filling & Stabilizing Applications
Concrete void filling and soil stabilization can be used in many different slab settings where hidden support loss has developed. Common applications include driveways, sidewalks, patios, steps, pool decks, garage floors, basement slabs, commercial floors, warehouse slabs, and agricultural concrete pads.
The right application depends on the slab condition, what is happening beneath it, and whether the goal is support only or support plus lift. Some projects need only concrete void filling and soil stabilization, while others may also need concrete lifting and levelling to correct settlement.
Our Concrete Void Filling & Stabilization Process
1. Assessing the Void & Slab Stability
Every concrete void filling and stabilization project begins with an assessment of the slab and the support conditions beneath it. We look for visible signs such as washout, hollow-sounding areas, settlement, cracking and slab edge gaps to determine where support has been lost and how the concrete is being affected from below.
2. Drilling Non-Invasive Injection Holes
Once the problem areas have been identified, we drill small 5/8-inch access holes through the concrete slab in strategic locations, typically spaced about 4 to 6 feet apart depending on the slab and the support conditions below. These minimal-impact holes allow us to inject polyurethane foam directly beneath the slab so it can reach hidden voids and unstable soils that need to be addressed.
3. Filling Voids & Stabilizing Soils with Polyurethane Foam
Next, we inject the polyurethane foam through the access holes and into the spaces beneath the concrete slab. Because the material starts as a liquid, it can flow into tight spaces, gaps and loose soils before expanding into a rigid foam that fills hidden voids, compacts weakened subbases, and delivers both concrete void filling and soil stabilization rather than simply occupying open space below the slab.
4. Patching & Surface Cleanup
Once the slab is successfully void filled and stabilized and any necessary lift is completed, we patch the small injection holes and clean the work area. Because the holes are minimal in size, the finished repair is far less invasive than mudjacking, and far cheaper than tearing out and replacing the slab.
Benefits of Polyurethane Foam for Concrete Void Filling & Stabilization
- Quick Curing & Minimal Downtime: One of the biggest advantages of polyurethane void filling and stabilizing foam is how quickly it cures. Most polyurethane foam-based slab repairs are ready for normal use within about 15 to 30 minutes, which means concrete void filling and soil stabilization can often be completed with very little disruption to your property or daily operations.
- Lightweight, But Strong Support: Unlike the heavier cement-based materials used in mudjacking that can get washed out over time, our polyurethane foam is lightweight and expands into gaps and weak soils without adding unnecessary stress on already compromised ground. Under pressure, it develops exceptional compressive strength, making it an effective solution for concrete void filling and soil stabilization in slabs affected by erosion, settlement, washout, and poor compaction.
FAQs About Concrete Void Filling & Soil Stabilization
What causes voids under concrete?
Voids under concrete are usually caused by water erosion, poor soil compaction, freeze-thaw cycles, plumbing leaks, groundwater movement, shrinking soils, root growth, or buried organic material breaking down beneath the slab. Burrowing animals can also create tunnels that displace supporting soil and leave behind empty spaces, which is why both the void and the underlying cause should be addressed to help prevent the problem from coming back.
How do you fill a void under a concrete slab?
A void under a concrete slab is typically filled by drilling access holes through the concrete and injecting a cement or polyurethane foam-based material beneath the slab until the empty space is filled and support is restored. With polyurethane foam, the material expands into hidden gaps, fills the void, helps compact loose soil below to improve the stability of the slab.
How much does it cost to fill a void under a concrete slab?
The cost to fill a void under a concrete slab depends on the method used, the size of the void, the slab condition, site access, and whether lifting or extra soil stabilization is required. Mudjacking usually costs less upfront, while polyurethane foam may cost more initially but offers a lightweight, fast-curing solution that is often better suited for long-term concrete void filling and soil stabilization.
At Slab-Jack Kings, our minimum charge for any void filling and stabilization project is $1,000 plus GST, and the most accurate way to price your repair is with a free estimate.
Free Concrete Void Filling & Soil Stabilization Estimates
Hidden voids beneath concrete can lead to cracking, settlement, and long-term support problems if they are left untreated. Our concrete void filling and soil stabilization services are designed to fill empty spaces beneath the slab, compact loose material, and restore more reliable support with our exclusive, custom-engineered polyurethane foam systems.
At Slab-Jack Kings, we offer free on-site estimates for concrete void filling and soil stabilization projects throughout Manitoba and Northwestern Ontario. We will assess your slab, figure out what is happening below the surface, and recommend whether your project is best suited for void filling and stabilization, lifting, or a combination of services.
Our minimum charge for any void filling and stabilization project is $1,000 plus GST, which helps cover base costs such as travel, material, labour, equipment maintenance, and repairs. If you are noticing hollow-sounding concrete, gaps beneath slab edges, signs of washout, or early settlement, request your free estimate today and let our family help you find the right repair solution.
For more information, please call, email, or text us using the chat bubble on the bottom right-hand side of this page. To get yourself in the queue, please fill out our online Request an Estimate Form.
