How do I know if there's a void under my slab?

Listen for a hollow sound when walking on the slab. Look for cracks that increase from edge to center, or gaps opening between the slab and adjacent walls or structures. A settled or tilted slab that was previously level is a strong indicator.

Can voids be filled without lifting the slab?

Yes — if the slab is at the right elevation but has a void beneath it, we can fill the void without lifting. This is preventive work to stop settlement before it starts.

Will filling the void prevent future settlement?

Filling the void addresses the current gap. Whether future voids form depends on the underlying cause. If it's drainage-driven erosion, improving drainage alongside void filling gives much better long-term results.

Is void filling different from mudjacking?

They use the same injection technique. The difference is intent: mudjacking is typically focused on lifting the slab; void filling may or may not involve lifting, depending on whether the slab needs it.

Void Filling and Soil Stabilization for Concrete in West Michigan

When a concrete slab settles, there's almost always a void beneath it. But sometimes a void forms without the slab settling yet — and if you don't address it, the slab eventually drops, cracks, or breaks.

Void filling and soil stabilization are what you do when the problem is in the ground, not just with the slab. This page explains what causes voids, how we find them, what we do about them, and when stabilization needs to happen before leveling.

What Creates Voids Under Concrete

Voids beneath slabs are more common in West Michigan than most homeowners realize. The usual causes:

Soil erosion: Water moving through sandy West Michigan soils can carry particles away from beneath a slab over time. The slab bridges the growing void until it's large enough that the concrete can no longer support its own weight. This is the single most common cause of residential slab settlement in Kent and Ottawa counties.

Plumbing leaks: A slow leak beneath a slab — from a water main, sewer line, or drain tile — creates a channel that erodes soil over months to years. The slab may not show any sign until the void is significant. If you're seeing unexplained water usage or wet spots, investigate before leveling.

Poor initial compaction: Concrete poured over insufficiently compacted fill settles as that fill compresses under load and over time. This is common in newer developments where fill material was brought in for grading.

Organic material decomposition: Old tree roots, buried wood, or organic debris beneath a slab decompose over time, leaving a void.

Freeze-thaw movement: Water enters beneath a slab at the edges, freezes, expands, and when it thaws, may not leave the soil in the same configuration — gradually creating voids over many cycles.

How We Detect Voids

Most voids aren't visible. We find them by:

Ground-penetrating radar (GPR): For commercial applications and large-scale investigations, GPR can map subsurface voids without any drilling.

Sounding: Tapping or walking on a slab reveals a hollow sound when there's a void beneath. A solid slab sounds dull; a voided one has a distinct ring or hollow resonance.

Visual indicators: Cracks that run from low to high elevation, gaps between a slab and adjacent structures, or doors and windows that don't open correctly can indicate movement from voiding.

Probe drilling: On jobs where we suspect voids in specific areas, we can drill a small probe hole to confirm and measure the void before injection.

Void Filling: How It Works

For most residential voids, we inject material through holes drilled in the slab — the same process as mudjacking or poly foam lifting. The distinction is intent:

Standard slab leveling — we're filling the void and using injection pressure to lift the slab.

Void filling only — we're filling the void beneath a slab that hasn't dropped yet, or beneath a slab we can't lift (perhaps because adjacent structures prevent upward movement). The goal is to prevent future settlement, not to lift the slab now.

Soil stabilization — in cases where the soil itself is the problem (highly erosive, sandy, poorly compacted), we may use a grout or chemical stabilizer injected into the soil to bind particles and reduce future erosion.

For most residential void filling, polyurethane foam is preferred because:

It expands to fill irregular void shapes
It's lightweight (doesn't add load to an already compromised subgrade)
It's hydrophobic, so it resists being washed away by groundwater

When Void Filling Comes Before Leveling

Sometimes the sequence matters. If you have:

Active water intrusion — fix the pipe or drainage issue first. Filling a void that's actively being re-eroded by water buys you months, not years.
Very large voids — if the void is deep or extensive, we may do a preliminary stabilization pass before attempting to lift the slab.
Unstable fill soil — if the material beneath the slab is too loose to support the slab after lifting, stabilizing it first produces a better long-term outcome.

We'll assess this on every job and tell you what sequence makes sense.

Commercial Void Filling

Commercial applications are where void detection and filling are most critical. A void beneath a warehouse floor, loading dock, or retail slab can cause:

Equipment damage from sudden slab failure
Trip hazards and liability exposure
Structural damage to racking systems anchored to the slab

We can work after hours to minimize disruption and use GPR to locate voids before they cause visible damage.

→ Commercial slab leveling page

What Void Filling Costs

Pricing depends heavily on the size and number of voids, depth, and method used. Rough residential ranges:

Small residential void (single slab area): $400–$1,200
Multiple voided areas: $1,000–$3,500
Large commercial void investigation + filling: Call for estimate