Kahgel is one of the oldest traditional mortars in Iran capabilities and performance of which in the past to conserve earthen buildings show that it can be used as a covering for conservation and preservation of earthen architectural structures. The ancient waterproof covering is very efficient at keeping the building dry during the heavy rain showers, but low durability and the need for renewal the plaster due to erosion of rainfall suggest that Kahgel plaster is weak and unstable. So, it is very essential and necessary to find appropriate scientific methods to enhance durability and lifespan of Kahgel plaster. In this research, the effect of silicates micronized additives (including Microsilica, Feldspar, Zeolite, Bentonite and Kaolin) on the stabilization and improvement of the physical and mechanical properties of Kahgel plaster with experimental study by hydraulic conductivity and water erosion Kahgel plaster indicated that using the micronized silicates additives can significantly improve physical and mechanical properties of earth and earthen materials such as Kahgel. Experimental results showed that application of Kaolin 150 microns at 3 wt% (by weight of Kahgel) reduced hydraulic conductivity of the Kahgel plaster at 65% level and Zeolite 45 microns at 3 wt% (by weight of Kahgel) decreased by 85%. In addition evaluation of water erosion of the samples during rainfall by rainfall simulator showed that use of 3 wt% micronized Microsilica, Feldspar, Zeolite and Kaolin decreased sample’s total dry material loss of the Kahgel plaster at least10/5% and maximum up to 37/7% and increased their durability against erosion from rainfall. In addition, results from studies indicate that by reducing the particle size of the additive, their positive effect on physical and mechanical properties of Kahgel mortar increases. On the other hand, 3 wt% is the optimized percentage of micronized silicate additives to improve Kahgel coating and increased amount of additives seems to have no significant impact on the improvement of physical and mechanical properties.