Rock-cut architecture represents a distinctive tradition of vernacular building that has persisted into the present day, with new examples continuing to be carved in northern Ethiopia. Rock-cut structures are often carved in rocks that have low strength, because of this inherent property they are deemed more vulnerable to deterioration. However, instances of such structures that have withstood decay forces challenges this assumption. This study investigates the durability of rock-cut structures carved from volcanic rock outcrops, with a focus on surface hardness measurements at rock-cut sites carved in the medieval period (Lalibela) and two newly carved sites (Dagmawi Lalibela and Debre Tsion) in northern Ethiopia. To evaluate how different exposure types and durations affect rock durability, surface hardness measurements of weathered, unweathered, and interior walls at Lalibela, as well as rock walls exposed for 1, 3, and 8 years at newly carved churches, were compared. The results showed that the rock-cut churches at Lalibela had a higher rock strength than the newly carved churches, which points to the level of sophistication in vernacular construction of the period. Moreover, the results showed that the longer exposure of rock walls lead to an increase in surface hardness in the newly carved churches. This was attributed to case hardening and bioaccumulation on the surface. These findings underscore that the long-term preservation of rock-cut structures depends not only on the properties of the rock but also on surface processes such as case hardening and bioaccumulation, which can significantly enhance durability even in low-strength materials.