The effect of external environment on the aging process of commercially used lime-cement plasters is studied. Three different kinds of plasters are tested at three different ages, namely in the reference state after 28 days of standard curing and after one and two years of exposure to the environmental conditions of Central Europe. The basic physical properties (bulk density, matrix density, open porosity), mechanical strengths (compressive strength, bending strength) and water vapour diffusion resistance factor belong to the studied properties. Experimental results show that not only the compressive strength but also all other studied characteristics are affected by the external environment in a significant way.