A variety of materials are used in construction, including brick, stone, plaster, mortar and concrete. They all interact with moisture in the air, with water adsorbing or diffusing through their pores.Characterizing the behavior of water in building materials is fundamental to understanding their interaction with the environment. Water also plays an important role in degradation processes such as crack formation and the chemical attack of concrete and cement by chlorides and sulfates. Differences in the sorption and water transport properties of different materials can, therefore, be used to help explain or predict their performance over time. Many naturally occurring substances, such as clay, sand, wood and rocks, even twigs and leaves have been used to construct buildings. Apart from naturally occurring materials, many man-made products are in use, some more and some less synthetic.