Two conditions must be present to create efflorescence:
1. A source of water soluble salts.
2. Water moving through the material to carry the salts to the surface. Water evaporates and leaves the white powder behind.
Efflorescence is a process not a thing. The process is actually water transporting any substance that it can carry to the surface. Substance can be a wide range of things such as iron oxides, concrete additives but usually water soluble salts.
There are two types of Efflorescence
1. Powdery – Result of water traveling though the concrete and evaporating on the surface leaving behind the powdery residue.
2. Crystalline – Occurs when powdery efflorescence is re-emulsified with water creating tightly bonded crystals on the surface. This is more difficult to remove and may require light sand blasting.
Removal of efflorescence can be as easy as applying a phosphoric acid to the surface. However, if the source of the water penetration is not addresses, efflorescence may reappear. In more server cases, light sand blasting may be required.