A brick is the basic ceramic element which is used to build masonry walls. Masonry however is a general term which indicates the assembly of relative small units to form larger entities such as walls. The materials which are generally used in masonry therefore also include elements such as stones or concrete blocks. These elements are generally held together by mortar which is a mix of sand, a binder (either cement or lime) and water. The binder can be of two types: hydraulic or non-hydraulic. Gypsum and lime are non-hydraulic binders. This type hardens in contact with air, in a process known as carbonation. When wet lime is exposed to air carbon dioxide is reabsorbed and the mortar hardens . Non hydraulic binds are cement and hydraulic lime. This type hardens in a process known as hydration which can occur irrelevant of the presence of water. During this process heat is generated when adding water (exothermic reaction).
Bricks are generally made of clay (which is a hydrous aluminum silicate containing calcium carbonate and iron oxides). Modern bricks are typically burned in continuously fired tunnel kilns.
The colour of bricks is determined by the proportion of hydrated oxide of iron and other ingredients they contain, also by the degree of heat in burning . If under burned the colour is pinkish-orange. These bricks tend to have low strength and low durability. If over burned or burned at high temperatures (like clinker bricks) the colour is dark. These bricks are partially vitrified, mechanically very resistant and impervious to water. These bricks also tend to be very dense and do not bond well with mortar.