How to Prepare Soil for a Concrete Slab

Remove the top layer of soil, including all the sod, with excavating equipment or with a shovel. While soil types vary in different geographical locations, the surface is usually unsuitable for pouring concrete. You may have to remove 5 inches or more of soft soil to reach the hard compacted soil.

Replace the removed soil with sand. Sand compacts well and provides an optimal base on which to pour concrete. The amount of sand you will need depends upon how much soil you removed. A concrete slab may be 4 to 6 inches thick, so add sand until it reaches the proposed bottom of your slab.

Pack the sand with a sand compactor, available from construction rental stores. You will run the compactor over the sand base and the machine will vibrate the sand, forcing the tiny particles to fill in tightly.