The regions of Zhouqu and Wudu in Gansu Province, China, experience some of the world's most severe debris-flow-related disasters, such as landslides and mudslides. The intensity of these events is attributed to the underlying Silurian slate lithology, which undergoes freeze–thaw and dry–wet weathering processes. In addition, the regional climate allows these processes to alternate, which intensifies the weathering of the slate. In this study, the physical weathering of slate was assessed using photographs and measurement of variations in characteristics such as quality, elastic velocity, stress–strain curves and uniaxial compressive strength. Varying numbers of cycles of either freeze–thaw or dry–wet weathering processes, or an alternating combination of the two cycles, were applied to samples. Rules defining the correlative index of slate weathering were established via correlation regression and fitting analyses. Variations in physical and mechanical properties in response to weathering were used to elucidate the weathering and behavioural mechanisms of the slate under the different weathering processes. The results also provided a reference for both evaluating slope stability and predicting the potential for debris-flow disasters within the study region.