The problems of wetting of masonry structures were considered: its causes, consequences and methods of humidity control. The classification of destructions that occur in the masonry as a result of its moistening was given. Destruction processes under wetting of different origin were briefly described. The experimentally ascertained impact of humidity on the strength of different kinds of brick was presented. The influence of this factor is often missed in the material testing and analysis of structures. The comparison between different methods of moisture control was given. A technique for measuring the moisture using the calcium carbide method was pictured; this method is little known in Russia. The advantages and disadvantages of non-destructive methods were discussed. Special attention was paid to the definition of errors in electrical control methods, occurring due to existence of salts in the masonry. The recommendations for combined use of different methods of humidity control were given.