Do You Add Rock First to Pour a Concrete Driveway?

Prepare the Site

• Preparing the site for a concrete driveway is the first and most laborious task. Once you've marked the borders and verified that the size is wide enough to accommodate one or two cars, the site must be excavated. The depth should be at least a foot, with the bottom sloped downward to the street. The soil at the bottom should be stabilized as much as possible with a compactor.

Build the Base

• Add the foundation rocks into the site in a series of 2-inch-thick layers. The stability of a concrete slab is only as good as its base. Compacting the rocks in each thin layer maximizes the overall quality of the driveway. Use 3/4-inch crushed rocks and build up the base until it is at least 8 inches thick. Typically, the base should fill 2/3 the depth of the foundation. For instance, if you're pouring a 5-inch-thick slab, the rock base should be 10-inches thick in a 15-inch deep site.

Poured Concrete

• If you're pouring a smooth slab, add the rocks into the mix and blend with water before pouring the concrete. The ratio for mixing your own concrete is one part cement, three parts sand and three parts rock. Use a concrete mixer to stir, then add small amounts of water until the concrete has a toothpaste-like texture. Pour the concrete over the rock base and spread it with a gauge rake. Before it sets, screed the surface to make it level and push a medium-bristled brush over top so it hardens with small grooves for traction.

Exposed Aggregate

• An exposed aggregate driveway is made from poured concrete with a layer of decorative rocks exposed across the surface. Rocks can be added before you pour the concrete, or seeded in the surface once it is poured, which gives you more control over the final appearance. Spread the stones over wet concrete with a broom and press them into the surface with a flat board. About 2 hours after the pour, use a soft broom to push off a fine layer of cement from the top of the rocks to expose them.