Void filling is the process of injecting material, whether cement slurry, polyurethane foam, or specialized grout, into empty spaces that have formed beneath a slab or foundation, preventing further settlement by eliminating the gap the structure would otherwise sink into.
These voids typically develop from soil erosion, poor original compaction, or water washing soil away from beneath a structure over time.
What Causes Voids Requiring Filling?
- Soil erosion from water infiltration
- Settling or consolidation of poorly compacted fill
- Pipe leaks washing away supporting soil
- Natural soil movement over time
Why Is Void Filling Important?
An unfilled void beneath a slab or foundation represents an area with essentially no support, meaning any load placed on that section has nowhere to transfer except further downward into the empty space, accelerating settlement. Filling these voids proactively, before significant settlement damage occurs, is often far less expensive than waiting until visible cracking or sinking forces a more extensive repair.
Identifying void locations before filling typically involves either visual inspection of visible settlement patterns or, on larger or less obvious projects, ground-penetrating radar to map subsurface gaps accurately before committing to a repair plan. Addressing a void promptly, before it grows large enough to cause visible settlement, is generally far less expensive than waiting until the resulting damage requires a more extensive repair. Simple visual cues, like a slab edge that’s noticeably lower than its neighbor, are often the first sign worth investigating. Catching this early is almost always cheaper than waiting for visible damage to appear. Early attention here consistently proves cheaper than delayed action.
Void Filling vs. Polyjacking
Void filling is the general goal of eliminating empty space beneath a structure. Polyjacking is one specific technique for achieving that goal, using polyurethane foam, while other void-filling methods might use cement slurry or specialized structural grout instead.