In order to effectively prevent cracking of concrete, and to ensure its structure is suitably strong, rebar must be placed correctly within the framework of the concrete mold, and spaced at intervals to prevent the formation of cracks. There is no set measurement for spacing rebar, unless you are a contractor building concrete walls within building codes. For the average home handyman building a patio, there are far fewer constraints.
Place four pieces of steel rebar within the concrete mold approximately 6 inches from the outer moldboard on each side. Fasten these pieces together firmly using the steel wire.
Place a piece of rebar in the center of the frame with its ends resting on the lower of the outer rebar pieces. Secure this piece in place with the steel wire. Place pieces of rebar parallel to this piece until there is approximately 1 foot of space between each piece.
Place rebar on top of these pieces in the same fashion, creating a checkerboard pattern and fastening each piece of rebar where it meets the lower rebar with the steel wire. Each open square should be approximately 1 foot square, but does not have to be exactly 1 foot.