Porosity is an important characteristic of brick. In contrast to other moulded or pre-cast building materials, the porosity of brick is attributed to its fine capillaries. By virtue of the capillary effect, the rate of moisture transport in the brick is ten times faster than in other building materials. Moisture is released during day-time and re-absorbed during night-time. The ability to release and re-absorb moisture by capillary effect is one of the most useful properties of brick that helps to regulate the temperature and humidity of atmosphere in a building. This distinctive property makes brick an admirable building material, particularly suitable for buildings in the tropics. On the other hand, all porous materials are susceptible to chemical attacks and liable to contamination from weathering agents like rain, running water and polluted air.