Slab Void Fill with Polyurethane Foam or Concrete
You might want to fill the voids in a concrete slab for many reasons. Maybe you’re concerned about potential sinkholes, a foundation disruption, or maybe uneven flooding. Filling the voids will make the slab more level and increase its load-bearing capacity. Two good choices for void fill are polyurethane foam and concrete.
Polyurethane foam is injected into the voids through small holes drilled in the slab. The expanding foam fills the entire void space, creating a solid mass that bonds well to the concrete. A concrete mixture is also injected into the voids, but it usually requires a much larger hole to be drilled. The concrete expands as it cures, filling the entire void space.