The possibility of using an alkyl alkoxy silane (AAS) (iso-butyltriethoxysilane) in mitigating alkali-silica reaction (ASR) has been investigated. Cement mortars were prepared with reactive aggregates of basaltic and siliceous origin. AAS was applied to the surface of test specimens. The accelerated mortar bar method (ASTM C1260) was employed for the detection of ASR-related expansions. In addition to the length change, total water absorption (ASTM C642) of mortars and penetration depth of AAS were also measured Three different curing procedures (short, medium, and long prewaiting periods) were applied to AAS-treated mortar bars before the ASTM C1260 tests. To understand the possible mechanism of prewaiting periods. on water repellency of AAS-treated mortars, Fourier-transform infrared spectroscopy (FT-IR) analyses were also performed.