Silane based surface impregnants improve the surface characteristics by imparting water repellency. However, wet conditions are not suitable for their effective performance. A concrete surface impregnant consisting of stearic acid, which exhibits both hydrophobicity and hydrophilicity, along with fatty acid to further improve the repellency in wet condition was developed. Concrete specimen surface was applied with varying amounts of impregnant and the surface moisture and surrounding moisture condition were also varied during application and after the application of impregnant to determine the effectiveness of the impregnant. The specimens were subjected to salt immersion test and accelerated carbonation test to evaluate the concrete surface resistance against deteriorating agents. The impregnant was found to be effective when applied under wet condition. The apparent chloride ion diffusion coefficient was suppressed regardless of the moisture condition of the concrete surface and the environment. On the other hand, reduction in water absorption rate and carbonation rate were more pronounced when applied to wet concrete.