Solution
Grout Injection: Fill Voids, Stabilize Soils, Stop Slab Settlement
When polyurethane foam isn't the right tool, grouting delivers controlled void fill and soil stabilization under heavy slabs.
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Grout injection — including cement grouting and chemical grouting — is used to fill large voids, solidify loose or washed-out soils, and arrest slab settlement in situations where polyurethane foam either cannot deliver enough fill volume or isn't appropriate for the soil type. In Middle Tennessee, sandy or loosely packed soils in Wilson and Maury Counties can be susceptible to void formation under slabs, and grout injection provides a denser, more permanent fill. It's also the preferred method when large driveways, garage floors, or commercial slabs have experienced significant differential settlement over an expansive void.
How It Works
Small holes (typically 1 to 2 inches in diameter) are drilled through the slab or foundation element at calculated injection points. A grout pipe or injection tube is set into each hole and the annulus is sealed. Cement grout — a slurry of Portland cement, water, and sometimes sand — is pumped under pressure into the void or soil column. The pressure drives the grout into voids, fractures loose aggregate, and permeates pore spaces in granular soils. For chemical grouting, polyurethane-based resins are injected to solidify and bind loose fine-grained soils without the weight of cement. Injection continues until grout return is observed at adjacent ports or until calculated volume is reached, confirming the void is filled. The material cures rigid and load-bearing within hours.
Problems This Solves
"Grouting is the right call when you've got a substantial void that foam alone won't fill adequately, or when the soil itself has lost its structure and needs to be bound back together. It's a more involved process, but it's the kind of repair that stays fixed."
How It Works
What to expect from start to finish.
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Site Investigation and Void Mapping
We probe and sound the slab to locate voids, then assess soil conditions. For large projects, ground-penetrating radar may be used to map void extent before drilling. Injection port locations are laid out to provide full coverage of the void zone.
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Port Drilling
Holes are drilled through the slab at the planned injection points. Port spacing is typically 18 to 36 inches in a grid pattern, adjusted for void geometry. Drill cuttings and any loose material are cleared from each hole.
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Injection Tube Setting and Sealing
Injection fittings are set into each drilled port and the annulus between the tube and slab is sealed with hydraulic cement or a mechanical packer to prevent grout blowback at the surface.
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Controlled Pressure Injection
Grout is pumped through each port under controlled pressure, starting at the lowest points and working outward. Pressure and volume are monitored continuously. Injection stops when grout returns at an adjacent port or target volume is reached for that zone.
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Port Plugging and Slab Patching
After grouting is complete and initial cure has occurred, injection ports are removed and the drilled holes are plugged with non-shrink grout and finished flush with the slab surface.
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Cure and Load Restoration
Cement grout reaches initial set in 4 to 8 hours and structural strength in 24 to 48 hours. Light foot traffic is typically permitted within hours. Full vehicle or equipment loads are held until the curing schedule is met.
FAQ
Frequently Asked Questions
When is grout injection chosen over polyjacking foam?
Polyjacking is faster and lighter, but for very large voids, heavy-duty slabs (loading dock floors, thick concrete aprons), or soils that need permeation rather than just void fill, grout injection provides more material volume and higher compressive strength. We evaluate both during the inspection and recommend the method that fits your specific situation.
Will the slab be lifted during grouting?
Grouting is primarily a void-fill and stabilization method, not a lifting method. Some minor slab movement may occur as pressure fills the void, but intentional lifting of a structural slab typically requires pier-assisted methods. If lifting is a goal, we'll discuss that during the inspection and may recommend a combined approach.
How many holes will be drilled in my slab?
Port count depends entirely on void size and geometry. A typical residential driveway panel might need 6 to 12 ports. Larger garage floors or commercial slabs may need significantly more. We map port locations before drilling so you know the full scope before work begins.
Is the patching noticeable after the ports are plugged?
The plug patches are visible as small circles — typically 1 to 2 inches in diameter — in the slab surface. They are flush and structurally sound, but will be visible, especially on finished or colored concrete. This is true of polyjacking as well. We can discuss sealing or surface treatment options if aesthetics are a priority.
Can grout injection fix a sinking foundation?
Grouting can stabilize soils beneath a foundation and fill voids that are causing ongoing settlement, but if the foundation has already moved significantly, piers are typically needed to lift and re-support the structure. Grouting and pier installation are sometimes used together — grouting to eliminate the void, piers to restore elevation.