The concrete slab should be at least four inches thick; it should be thicker if heavy machinery will be resting on it. Building codes specify the concrete mix, which varies by area. The criteria are described in terms of "compressive strength," which is essentially the quantity of water in the mix. The higher the compressive strength, the better. The type of reinforcement used in the slab affects its durability. Reinforcement includes wires or bars that give the slab its strength and keep it stable. There are two main types: rebar for concrete floors and walls, and mesh for ceilings. Rebar is woven into the concrete while it's wet to provide extra strength. The length of the bar determines how deep it goes into the slab. For example, 6-inch-diameter rebar goes about 2 inches into a 4-inch-thick floor. Ceiling rebar is usually only as deep as needed to reach the top plate of the ceiling. Then another piece of rebar is added on top of that. This process is repeated until the entire ceiling is reinforced. Mesh is a network of wire strands placed between the ceiling and roof panels of a garage to prevent objects from falling through. The thickness of the mesh depends on how much weight will be supported by it. Garages tend to support some degree of traffic movement and typically have a suspension system to reduce vibration when vehicles enter or leave the garage.