The degradation of a thin layer of adhesive on a grit-blasted aluminium substrate, as a result of aqueous attack, was investigated and compared with the behavior of the adhesive on a grit-blasted aluminium substrate treated with gamma-glycidoxypropyl trimethoxy silane (GPS). The degradation study was achieved by examining aluminium coupons treated with adhesive that had been immersed in water at 25 degrees C and an elevated temperature ( 50 degrees C) for various treatment times ranging between 10 min and 1 day. All samples were characterized using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS and ToF-SIMS data indicated that the adhesive layer on both types of substrate was readily displaced by water. This is shown to be a two-stage process with bond rupture being identified by ToF-SIMS analysis and the displacement of the organic phase occurring at a later stage, as indicated by the XPS analysis, which showed a reduction in surface carbon concentration. When the substrates were directly in contact with water, a hydration process occurred and hydrated oxide species were formed on the surfaces. The results indicated that the hydration process was a postfailure event.