Polylevel polyurethane foam is pumped beneath concrete stairs through tiny ports about the size of a penny. Initially, Polylevel flows like water, filling even the smallest cracks and crevices in the soil. It quickly expands and hardens, lifting the concrete slabs above it and compressing the soil around it at the same time. Polylevel is waterproof, so it will never wash out, and it won’t degrade over time due to temperature extremes. It’s environmentally friendly, too, with no environmentally harmful chemical leaching. Best of all, Polylevel cures quickly, allowing your concrete to be used normally the same day.