This process employs high-density polyurethane plastic, instead of cementious grouts, to lift, re-align, underseal and void-fill concrete slabs which are resting directly on base soils. We inject liquid components using small (5/8") drilled holes directly through the concrete. As the plastic expands, voids are filled and a controlled mold pressure is exerted to re-support the affected slab. The polyurethane quickly cures into a strong, stable and long-lasting replacement base material. Our process is used on sidewalks, patios, driveways, garage and basement floors, and porches, as well as commercial buildings, highway, airport runways, bridges, parking areas and a broad spectrum of other concrete slab-on-grade facilities.