The external flooring is the laying of a floor outside the buildings. The main characteristics that external pavements must have are high resistance to mechanical actions caused by the sliding of vehicles and therefore of heavy vehicles, adequate non-slip, especially in case of wet surface, or in case of ice, this especially in the case the passage of pedestrians and therefore in public areas, but also in areas occupied by motor vehicles. So wear resistance and friction coefficient are the most important attributes they must have. In case of unfavorable climatic situations, the durability of the flooring must be guaranteed. In addition to this there must be an ease of maintenance, especially in the case of urban centers, where we usually find a frequent restoration of the surface appearance, but above all, frequent signs can be placed. These floors are formed by a surface layer that can be made with various materials such as stone slabs or ceramic tiles, concrete blocks, tiles and flat concrete slabs, and by a support whose characteristics vary according to the nature of the soil , the type of flooring and the expected loads. The floor under the flooring is called the subfloor, which provides the support for the flooring. Special purpose subfloors like floating floors, raised floors or sprung floors may be laid upon another underlying subfloor which provides the structural strength. Subfloors that are below grade (underground) or ground level floors in buildings without basements typically have a concrete subfloor. Subfloors above grade (above ground) typically have a plywood subfloor. The choice of material for floor covering is affected by factors such as cost, endurance, noise insulation, comfort, and cleaning effort. Some types of flooring must not be installed below grade, including laminate and hardwood due to potential damage from moisture.