Site Work Preparation for Pouring a Concrete Slab

Excavate the building area and clear any rocks, vegetation and root systems. Dig out a recess over the site 8 to 12 inches deep, depending on the purpose of the concrete slab. You'll need to dig deeper if the slab is meant for a building foundation or driveway.

Compact the bottom of the expanse to squeeze air pockets and moisture from the soil.

Level any high areas surrounding your building site or redirect the slope away from the foundation about 1/8 inch for every foot of distance. Install a drainage system around the perimeter of the land, at least 10 feet from the pour site, to direct rain water away from the concrete.

Add 4 to 8 inches of ¾-inch aggregate fill to the excavated area to improve the drainage of the site, support the concrete and pad it from frost heaves. Compact the aggregate until it resists pressure from the machine. Lay wire mesh over the aggregate to reinforce the concrete.

Set rebar over the compacted aggregate near the sides and across the center, about every 4 feet. If your slab is small or meant for light use, rebar is not necessary.

Frame the interior walls of the recess with 2 by 4 inch boards positioned on their sides. Stack the boards to cover the depth of the expanse and attach them with screws. The poured concrete will take the shape of the frame boards. You can remove the boards once the concrete hardens.