Efflorescence includes the water-soluble salts precipitated on the wall by water evaporation. The substance appears with building construction or after the completion of construction on the façade.
There are typically sulfides, particularly Preet (iron sulfide) in bricks. These sulfides are oxidized during burning and produce SO3. SO3 reacts with oxides present in clay, and creates calcium, sodium, potassium and magnesium sulfates.