Although mortar is an important source of the salts of efflorescence, it is by no means the only one. Masonry units may contain appreciable amounts of salts which are dissolved by moisture and brought to the surface when the units weather. In the case of bricks a standard test may be made to show their capacity to contribute to efflorescence through soluble salt content. A brick is placed on end in a pan of distilled water for seven days, in which time water is drawn upwards through the brick and evaporated from the surface. Soluble salts in the brick are taken into solution by the water and on its evaporation are deposited on the surface.
Efflorescence frequently forms on brickwork adjoining concrete units.
A good example of this is its occurrence beneath concrete window sills. In such a situation concrete frequently is wetted from rain and snow melting on it, and soluble salts of the concrete are dissolved and may be carried into the brickwork beneath. Salts which cause efflorescence may also originate in the back-up masonry behind the facing of a wall. Initially, the face may be free of salts, but later become contaminated from salts of the backing materials. Prolonged dampness in walls also promotes efflorescence.