A concrete slab is common structural element of modern buildings. Horizontal slabs of steel reinforced concrete, typically between 12 and 20 inches thick, are most often used to construct floors and ceilings, while thinner slabs are also used for exterior paving. Sometimes these thinner slabs, ranging from 2 inches to 6 inches thick, are called mud slabs, particularly when used under the main floor slabs or in crawl spaces.
French drains are primarily used to prevent ground and surface water from penetrating or damaging building foundations. Alternatively, French drains may be used to distribute water, such as a septic drain field at the outlet of a typical septic tank sewage treatment system. French drains are also used behind retaining walls to relieve ground water pressure.