Grout Injection Fills the Voids That Allow Foundations to Sink
When erosion or soil compression creates voids beneath a foundation or slab, grout injection fills them before the unsupported concrete can crack or sink under load.
On cost: $800 to $4,000 depending on void size and number of injection ports required.
Overview
Grout Injection for Foundation Voids
Voids beneath concrete slabs and foundations develop when soil erodes, compresses, or is washed away by water movement. An unsupported slab spanning a void will crack and sink as the concrete deflects under load. Grout injection, also called pressure grouting or slab grouting, fills these voids by pumping a cement-based grout through small-diameter ports drilled through the concrete. The injected grout flows into the void, fills it, and sets, restoring continuous soil support beneath the slab before structural damage can escalate.
Small holes, typically 1.5 to 2 inches in diameter, are drilled through the concrete slab at strategic locations above the suspected void. A pump injects a flowable cement-sand grout mixture through each port under controlled pressure. The grout fills the void, flowing outward from each injection point until the void is fully filled. When the pressure at adjacent ports begins to rise, the void has been filled and injection is stopped. The ports are patched and the surface is returned to its pre-injection condition. Grout injection is done with the slab in place and does not require excavation.
Wondering if this is the right fix for what you are seeing? Learn more about the warning signs: Bouncing or Springy Floors and Bowing Basement Walls . Or browse the full Problem Signs library for foundation repair.
Installation Process
How we install grout injection for foundation voids
Void Mapping
We identify the location and approximate extent of voids beneath the slab using sounding, tapping the surface and listening for the hollow response that indicates an unsupported area, and in some cases ground-penetrating radar for larger areas.
Port Drilling
Injection ports are drilled through the slab at a grid pattern across the void area, typically spaced 3 to 5 feet apart. The grid spacing is adjusted based on the estimated void volume and the grout's expected flow characteristics.
Grout Mixing and Injection
A cement-sand grout mix is prepared at the appropriate consistency for the void size and soil conditions. Grout is pumped through each port in sequence, monitoring pressure and volume to track void filling.
Pressure Verification
Pressure readings across the injection field are monitored. Rising pressure at adjacent ports indicates that the grout has filled the void and is beginning to meet resistance. Injection at each port is terminated at the appropriate pressure.
Port Patching and Cure
After injection is complete, all ports are filled with hydraulic cement or epoxy patching compound and finished flush with the slab surface. Grout typically achieves working strength within 24 hours.
A void under a slab is a ticking clock. The slab is spanning it, and every load cycle is stressing the concrete across that unsupported span. Fill it before the slab cracks, and you stop the problem. Wait until it cracks, and now you have two problems.
Why Ground Up
The difference is in the diagnosis
Get several quotes and you'll see a wide range of prices. The gap isn't luck. It's whether the contractor finds the actual cause and stands behind the work.
- In-house certified crews: we never subcontract your repair
- Optional independent third-party engineer review on larger jobs
- Honest three-tier triage: we tell you what can wait, in writing
- Family owned from the same Shelbyville Highway address since 2009
FAQ
Grout Injection for Foundation Voids questions
Grout injection fills voids with a cement-sand mixture that sets permanently and does not degrade over time. Polyurethane foam injection also fills voids and can also lift the slab slightly. Grout is generally preferred for large voids or when long-term strength and permanence are the priority. Foam is faster-curing and can be more precise for slab leveling. We evaluate which approach is appropriate for each situation.
Grout injection is primarily a void-fill and support-restoration technique. It can produce modest slab lifting as the void is filled and pressurized, but it is not as precise for lifting applications as polyurethane foam. For significant slab lifting, returning a noticeably settled section to level, mudjacking or polyurethane foam lifting is typically the preferred approach.
A typical grout injection project for a residential-scale void can be completed in one day. Larger areas or multiple void locations may take two days. The slab can typically be walked on within a few hours of injection and returned to vehicle traffic within 24 hours.
Grout injection fills existing voids but does not address the cause of void formation. If erosion or soil compression created the original void, correcting the drainage or soil conditions that allowed it to form prevents new voids from developing in the same location. We assess the cause of the void as part of the project and provide drainage or soil recommendations alongside the injection work.
Cost depends on the volume of grout required to fill the void, which corresponds to the void size and depth. Small voids requiring a single injection point are among the least expensive foundation interventions. Larger void areas require more material, more ports, and more labor. We provide specific pricing after assessing the void location and extent.
More Solutions
Other solutions we offer
Carbon Fiber Strap Installation
Carbon fiber straps are high-tensile-strength composite straps bonded vertically to the face of a bowing basement wall to prevent further inward deflection. The straps are made from the same carbon fiber used in aerospace and structural engineering applications, rated at tensile strengths far exceeding steel by weight. When epoxy-bonded to a properly prepared wall surface from floor plate to sill plate, carbon fiber straps transfer the lateral soil pressure load into the top and bottom bearing points of the wall system rather than allowing the wall face to deflect. Carbon fiber reinforcement is best suited for walls that have deflected less than 2 inches and have not experienced significant cracking through the wall section. It is a hold-in-place system, not a restoration system, it prevents further movement but does not push the wall back toward its original position.
Deep Foundation Systems
Deep foundation systems transfer structural loads from the ground surface to soil or rock at a depth where bearing capacity is reliable and unaffected by surface conditions. In Middle Tennessee, the primary driver for deep foundation work is the region's expansive clay geology: the top several feet of soil shrink in dry weather and swell in wet weather, making them unreliable bearing material for foundations that must remain stable year-round. Deep foundation elements including helical piers, push piers, and micropiles penetrate through this active zone and reach bedrock, dense gravels, or competent clay at depth where moisture variation has minimal effect. These systems are used for both new construction on difficult sites and for repair of existing foundations that have settled due to inadequate bearing in the near-surface soils. Ground Up designs and installs deep foundation systems for residential and light commercial applications throughout the Middle Tennessee region.
Epoxy Crack Injection
Epoxy crack injection is a structural repair method for concrete foundation walls, slabs, and beams that have developed cracks due to settlement, curing shrinkage, hydrostatic pressure, the outward force of water pushing against a foundation wall from saturated soil, or thermal movement. Low-viscosity epoxy resin is injected under low pressure through surface ports installed across the crack at regular intervals, filling the crack from its deepest point outward. As the epoxy cures, it bonds the two concrete faces together with tensile strength greater than the surrounding concrete. The result is a monolithic repair that restores the structural continuity of the cracked section. Epoxy injection is appropriate for dry or dormant cracks, cracks that are not actively wet and not in active movement. For cracks with active water seeping through them, polyurethane foam injection (which expands and seals in the presence of moisture) is often the appropriate first step, followed by epoxy once the wall has been dried out.
Expansion Joint Installation
Concrete is a rigid material that nonetheless moves with temperature, moisture, and loading. In Middle Tennessee's climate, with summer temperatures regularly exceeding 95 degrees and occasional hard freezes in winter, the thermal expansion and contraction of concrete slabs, driveways, sidewalks, and foundation walls is significant. When concrete cannot move freely, it builds up internal stress that is released suddenly as a crack. Expansion joints and control joints are planned gaps in the concrete that give it a place to move without cracking in the field of the slab or through a structural element. Ground Up installs expansion joints during new concrete work and cuts or installs retrofit joints in existing concrete to prevent crack propagation and protect adjacent structural elements from impact loading caused by slab movement.
Foundation Underpinning
Foundation underpinning is the process of extending the effective depth of a foundation's bearing capacity by installing structural support elements that bypass inadequate near-surface soils and transfer load to competent material at depth. In Middle Tennessee, where expansive clay soils lose and regain bearing capacity with every moisture cycle, underpinning is the most durable long-term foundation repair strategy available. Ground Up installs two primary types of underpinning: helical pier underpinning, which uses rotating steel shafts with helical plates to reach bearing at a torque-confirmed depth; and push pier underpinning, which drives steel pipe sections hydraulically using the building's weight as a reaction force, meaning the home's own weight gives the hydraulic ram something to push against, until the pier reaches refusal in competent soil or rock. Both systems transfer the structural load from the clay soils that are causing settlement to deep bearing material that is unaffected by surface moisture variation, stopping settlement and in most cases allowing partial to full elevation recovery.
Concrete Piers for Foundation Support
Concrete piers are cast-in-place or pre-cast reinforced concrete elements that extend from the foundation footing down through unstable near-surface soils to a bearing stratum with adequate capacity. They are one of the most durable underpinning approaches available for residential and commercial foundations in Middle Tennessee, providing a permanent structural connection between the foundation and the stable soil or rock below the depth at which seasonal and moisture-driven soil movement occurs.
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