Buildings deteriorate for many reasons, including exposure to the elements and air pollution. Depending on the materials used to construct the building, exposure to weather over time will cause deterioration unless maintenance is performed regularly. Builders should consider local weather and environmental conditions before choosing certain stones and building materials.
Many 20th century buildings were made from concrete, which deteriorates over time. The main reason for this is corrosion, which falls into two main categories -- general corrosion from carbonation and pitting corrosion from chloride ions. Carbonation exposure to reinforcement structures over long periods can cause widespread cracking. Exposure to chloride ions from water that leaks into the concrete can cause pitting corrosion.
Salt crystallisation is a common reason that buildings made of stone suffer from deterioration. Salt crystallisation tends to effect porous stone. Typically, salt enters the stone through the air and into the pores, where it then crystallises. It causes the stone to deteriorate, usually into a fine powder. Salt is often the result of the mixing of air pollutants and stone. It also comes from groundwater, sea spray and chemical cleaners.
Frost damages buildings. Stone structures in areas exposed to freezing temperatures as well as rain or snow are susceptible to this damage. Frost damages stones with small pores more than it does those with larger pores. Buildings in northern England and Scotland will suffer most from frost damage due to the colder climate.
Life itself can take its toll on a building. Plants and plant roots, ivy, birds and micro-organisms can speed up decay. Bacteria, fungi and algae cause the most damage because they attack carbonate and silicate minerals with acid and other chemicals. These minerals are found in many types of stone.