Physical and mechanical characteristics, the most significant for the plasters with regard to the features of their behavior as the coating of building faces were evaluated. Results of quantitative estimation of stresses in the plaster layers on surfaces of different stiffness due to the plaster shrinkage are given. It is shown that with a decrease of the surface modulus of elasticity, stresses in the plaster coating are decreased either due to reduction of the effect of its deformations’ constraint. By analysis and with experiments it is proved, that the main factor evaluating the ultimate extensibility of the mortar is its viscoelasticity modulus, while mortar strength increase involves its stresses increase.