Since using Si based ceramics as a structure material of combustion chambers, gas turbines, thermal isolating coatings are focused to the EBCs. Water vapor is the one of limitations of EBCs because of loss of Silicate. In this study, we have investigated effect of water vapor on the silicate structure for various temperatures and times on different coating compositions. The coatings were manufactured as three layers substrates. The first layer is MCrALY as a bond coat, second layer is YSZ. The top coat was manufactured various compositions with a mullite and different silicates. Experimental was performed 500, 1100°C and for each temperatures  100, 150, 200h. The coating were characterized with XRD, SEM, AFM DTA.