Void filling is the injection of polyurethane foam into empty spaces beneath a concrete slab, footing, or structure to restore full soil contact and support, often without lifting the slab.
In depth
Voids form when water washes soil out from under concrete, when soil shrinks, or when the ground was never properly compacted. Left alone, an unsupported slab flexes and eventually cracks or sinks. Void filling injects expanding foam that flows into the empty space, presses against the surrounding soil, and re-establishes uniform support from below.
Because the goal is support rather than lift, stabilization-specific foam is used so the material spreads laterally and fills the void with minimal upward force, keeping the slab at its current elevation.
How Acme applies it. For most void-fill work Acme uses RR-501, a 5-lb/ft3 stabilizing foam engineered to spread and fill rather than lift. On one warehouse floor, Acme injected roughly 500 pounds of foam to fill nearly four cubic yards of void and eliminate slab movement.
Related terms: Concrete Stabilization, Under-Slab Void, Undersealing, Soil Washout, Deep Foamjection
Frequently asked questions
Can void filling be done without lifting the concrete?
Yes. Stabilization foams like RR-501 spread laterally with minimal upward force, filling the void and restoring support without changing the slab’s elevation.
How soon can the surface be used after void filling?
Most surfaces are ready for full use within 15 to 30 minutes of injection.