Concrete Patio Preparation

Site Preparation

• Site preparation for a concrete patio includes surveying and staking the building site. For a do-it-yourself project, surveying includes measuring the site and marking the position of the excavation. Marking tools may be simple, such as lines drawn in the dirt, or more accurate, such as layout lines of marking paint, stakes and string line. Accurate site preparation requires layout that indicates not only the length and width of the patio area, but also the depth to which excavators must dig the slab's base.

Excavation

• Once the site is measured and marked, builders break ground and remove soil to make room for the concrete slab. Whereas small-scale concrete patio projects might require only manual excavation tools, such as a shovel and wheelbarrow, large projects require excavation equipment, such as loaders and backhoes. Excavators remove soil to create the rough form of the slab and to allow room for the concrete patio base layer of aggregate. Additionally, contractors or homeowners must consider where to deposit the dirt removed from the excavation area. If your property cannot accommodate the soil, you'll have to make arrangements for hauling and disposal.

Forming

• Concrete workers build a framework of lumber, called a concrete form, to contain and shape freshly poured concrete. Concrete forms typically consist of separate pieces of dimensional lumber, such as 2-inch by 12-inch framing lumber, connected at corners and held in place with wooden or metal stakes. A concrete form is essentially a large sandbox. The size of a concrete patio's form-work must accommodate the slab's substrate, such as gravel, and the thickness of the slab.

Substrate

• The term "substrate" refers to a layer of material that rests between the earth and a concrete slab. The substrate separates the concrete slab from the heaving, swelling, freezing and thawing of the ground. Depending on engineering plans and local building codes, concrete patios require a layer of gravel and sand several inches thick to more than a foot thick. Concrete workers dump the substrate into the excavated area and spread the material into a smooth, even layer.