A formulation of a lime plaster dry building mix with polysaccharide additives designed for exterior finishing work has been developed. The issues of the finishing layer influence on the heat and humidity conditions of building enclosing structures are considered using four types of dry building plaster mixes and three types of enclosing structures as an example. The amount of condensate falling out is analyzed depending on the type of structure and time of operation. It is established that the presence of a finishing layer based on dry building mixes on the outer surface of the enclosing structure contributes to the shift of the zero isotherm. It was found that in walls made of foam blocks without insulation, condensation will fall out in the foam concrete layer. The use of plasters based on dry building mixes Porotherm LP, VerMix ShN50 and on the basis of the proposed lime plaster eliminates the formation of condensate in the thickness of structures made of expanded clay concrete with insulation and brick with insulation. The expediency of using a dry building mix based on the developed lime composition with additives of polysaccharides is formulated.