At this article it has been considered the questions concerning the occurrence of efflorescence on the surface of buildings’ exterior walls made of vibropressed concrete blocks. The chemical and mineralogical composition of efflorescences were investigated using the electron-scan microscope and diffractometer. The mechanism of the efflorescence occurrence was disclosed The suitability of hydrophobization as a purifying method of the above mentioned walls from efflorescences was analyzed. The results of full-scale testing of proposed methods are given.