The effect of a cement–bentonite grout material was studied through glass/steel interactions. Hence, two experimental mock-ups, consisting of a “sandwich” of four materials in contact, stainless steel/AVM glass/AVM glass/P285NH steel, were leached by Callovo–Oxfordian poral water at 70°C for 1 year. CBG material was added for one experiment, whereas the second one was CBG-free. Chemical and structural analyses (scanning electron microscopy–energy-dispersive X-ray spectroscopy, Raman), performed mainly at the AVM glass/P285NH interface, evidenced a comparable alteration with and without the CBG. Indeed, its presence did not impact the gel formation by hydrolysis/condensation mechanism. For both experiments, the glass alteration rates corresponded to $r_0^{Cox,70°C}\over 32$, highlighting a kinetic rate drop after a 1-year leaching period. However, the CBG impacted the pH solution initially buffered by the claystone, promoting precipitation of Mg/Fe-rich silicates on the gel surface. Regarding P285NH corrosion, no major difference was observed with the CBG. Steel corrosion layers in both experiments were Si-free, and the corrosion rates were similar. Therefore, after 1 year at 70°C, the CBG had a limited effect on the glass/carbon steel interactions.