Long portions of the Apulian coast are steep cliffs in carbonate soft rocks. These, especially the calcarenite, are affected by weathering processes that markedly alter their mechanical properties with time, potentially leading to instability of coastal geomorphological structures. Such alterations are mainly due to chemical reactions between the solid and fluid phases, and are driven by chemical variables, which are internal variables and hence uncontrollable. In a search for the variables that drive the process of rock weakening, recourse is made to the micro scale, at which most of the chemical processes are observed and quantified. Observations using scanning electron microsope, thin sections and X-ray computed tomography analyses appear to be crucial for the understanding, interpretation and definition of the degradation mechanisms of the material. A chemo-mechanical coupled model at the meso scale of the chemically reactive stressed porous system is presented and framed in the context of a multi-scale scenario of an array of coupled phenomena. An analogous model at the macro scale is developed in parallel together with upscaling and identification procedures for meso-scale and macro-scale material constants. The main outcome of the study is a tool for predicting the progress of time-dependent weathering phenomena, potentially allowing the stability of geological structures to be assessed as it evolves with a progressing chemical degradation in a specific configuration and under a specific set of loads.