Step 5 · Backfill and Pour Concrete
Before this step, you must have your under-slab plumbing inspected and approved. Once you have the green light from the inspector, carefully backfill the trenches with the excavated soil and gravel. Use a tamper or the end of a 2x4 to compact the fill in layers (every 6 inches) to prevent future settling. Lay down a plastic sheeting vapor barrier over the fill to match the rest of the basement floor. Mix ready-mix concrete in a wheelbarrow or mixer according to the manufacturer's directions. Pour the concrete into the trenches, ensuring it fills all voids. Use a trowel or screed board to level the new concrete with the existing slab, and a concrete float for a smooth finish. Allow the concrete to cure fully, which can take several days.