Epoxy resins still remain controversial materials, due mainly to their low light-resistance. The necessity of hardening in a dry atmosphere and at a certain temperature can also be regarded as disadvantages. On the other hand, epoxy resins have become irreplaceable because of their evident advantages such as high adhesive power, and good temperature, chemical, and water resistance. Numerous stone, wooden, brick, ceramic, china and glass objects have been saved in Poland thanks to the application of these resins. The state of preservation of three portals (portal of the Eskens' House in Torun, restored in 1966; portal from Olbin in St. Mary Magdalene Church in Wroclaw, restored in 1968; portal of a house in the Old Market in ToruRn, restored in 1969) is the basis of evaluation used in this paper. It is concluded that a monument free of water-soluble salts is guaranteed to resist at least several decades. The objects treated in the correct manner have not changed in color after several years. Epoxy resins should be applied as dilute solutions in selected solvents. That selection plays a decisive role. The solvents recommended are listed. The physical process of impregnation and the climatic conditions under which to operate are also described. Possible microbial deterioration is studied, and tables on the susceptibility of stone samples and mortars to fungal growth show the results of this investigation.