Crystallisation of salts

• Soluble salts may be present initially in certain building materials or may be conveyed into them by movement of moisture from the ground or adjoining materials .
• When moisture gets into a material & evaporates from the surfaces , the concentration of the salts in solution increases until finally it crystallize out .
• If this occurs within  the pores of the surface layer and not on the surface , it may cause gradual erosion or flaking .
• On the surface it is referred to as efflorescence which cause some surface disfiguring only .
• If crystallisation takes place below the surface , it can cause more serious problems .