How to Prepare Soil for a Concrete Patio

A concrete patio.

The soil below a concrete patio must be carefully prepared so the patio will be mostly level. All patios need a slope built in to allow water runoff away from your house. The soil must also drain water well, so the patio does not crack during freezes and thaws. Learn how to prepare the soil below a concrete patio with these tips.

Soil Slope

Dig the below-grade basin for the patio so that the slope drops 1/4 inch every 4 feet in length and width away from the house. This will direct runoff, preventing basement seepage and flooding. The total depth of the patio basin should be 8 inches.

Soil Drainage

If the soil has a high percentage of clay, add soil aggregate in the form of coarse sand and large gravel and mix together to a depth of 4 inches above the basin floor. Level the basin floor for the patio in keeping with the slope requirements. After adding aggregate, compact the soil with a roller, and leave the soil slightly damp so it does not draw moisture out of the concrete as it cures.

Reinforce the Concrete Slab

Insert size 4 rebar beams into the concrete patio basin at 12-inch intervals in both directions. Tie wire loops at the rebar intersections.