The barrier performance of silane/clay nanocomposites as a coating material on concrete structure has been evaluated under different accelerated weathering tests, including moisture permeability and salty water spray. The silane/clay nanocomposite was fabricated by curing the silane–organoclay mixture through hydrogen bonding with concrete. XRD analysis indicated an improved intercalation of clay after adding into the silane solution. SEM examination of the coated concrete surface confirmed that the nanocomposite can effectively cover the pores and voids present on the concrete surface. The rheological study revealed a linear increase in viscosity with the addition of clay. Wetting properties were evaluated via contact angle measurements. The moisture permeability test showed that the permeability was substantially reduced due to the presence of clay of high aspect ratio. The salty water spray tests indicated the distinct barrier characteristics of silane/clay nanocomposite coating on concrete structure.