During the hydration of the mortar a reaction occurs between water and cement. This reaction forms high concentrations of free calcium. Directly after the masonry is finished, the mortar will start curing. Curing is caused by the reaction of calcium and CO2 from the air. Calcium and CO2 react to form calium carbonate (carbonation). This calcium carbonate is hard, and not-soluble in water. If the supply of CO2 is hindered, by the presence of excess water, for example, the carbonation reaction will be prevented. The presence of water caused by rain during construction, will result in high concentrations free calcium in the brickwork. When the calcium migrates to the surface upon drying, it will then react with CO2 at the surface and form visible white calcium deposits.