Soda-lime-silica float glass has been exposed to accelerated weathering conditions (95% relative humidity at 40 deg C) for periods of time varying from 3-49 days. Nanoindentation of the exposed samples has revealed significant differences in the hydration behaviour of the tin side and the air side of float glass. The nanohardness of the air side is initially lower than that of the tin side and this value is further reduced after only 3 days exposure to 95% r.h. at 40 deg C and continues to drop significantly with increasing exposure time. In marked contrast the nanohardness of the float side is relatively little affected by the exposure to 95% r.h at 40 deg C. Similar results are obtained for the reduced moduli of the surfaces. These data confirm that the presence of tin significantly reduces the rate of near surface hydration of float glass as compared to the air side, as they show that a deep layer develops on the air side over 7 weeks of accelerated weathering, whereas the equivalent layer on the tin side is of negligible thickness.
