Earthen-based structures, including invaluable heritage sites found worldwide, are particularly vulnerable to climate-induced moisture hazards due to their porous nature and sensitivity to water. Among these, the Wupatki Pueblo in Arizona, USA, represents a critical case study. Its Moenkopi sandstone masonry walls with earth-based mortars are experiencing accelerated degradation under increasingly harsh environmental conditions due to climate change. Recent extreme climate events, such as intense rain and snowfall, combined with no longer efficient drainage, have led to water accumulation, snow deposits and salt crystallization at the base of walls, threatening their structural stability and material durability. In this context, four representative test walls were built at Wupatki Pueblo using sandstone units from the Moenkopi formation and earth-based mortars prepared with locally sourced soil, aiming at evaluating the hygrothermal behaviour of the masonry. Temperature and moisture sensors embedded within the mortar joints enable continuous monitoring of hygrothermal conditions, with local environmental data being recorded through a weather station installed onsite. This paper focuses on the experimental characterisation of the materials used in the construction of the test walls, specifically their physical and hygric properties. Tests included direct bulk density measurements for the mortar and vacuum saturation tests for the sandstone to determine bulk density and open porosity. Additionally, the hygric behaviour of both materials was studied using water absorption and wet cup tests. Given the sensitivity of earthen mortars to water, the adaptation of standard testing protocols for hygric properties is also explored. The results provide essential input for the future development of multiphysics models to simulate the hygrothermal performance of Wupatki Pueblo’s masonry under changing environmental conditions.