Marés Stone and Structural Slenderness: A Material-Based Diagnostic Study of Palma Cathedral

The Palma Cathedral, a landmark of Mediterranean Gothic architecture, features some of the most structurally daring slender piers in European ecclesiastical design. This study examines the role of marés stone—a local marine calcarenite—in enabling such architectural feats despite its inherent fragility. A multi-technique, non-invasive diagnostic campaign was conducted, including visual inspection, portable microscopy, and infrared thermography, to evaluate the physical condition and behavior of the stone under structural and environmental stress. The results reveal widespread deterioration processes—granular disintegration, alveolization, biological colonization, and structural cracking—exacerbated by the stone’s high porosity and exposure to marine aerosols and thermal fluctuations. Thermographic analysis highlighted moisture retention zones and hidden material discontinuities, while crack monitoring confirmed long-standing, localized structural strain. These findings demonstrate that the Cathedral’s formal audacity was grounded in a refined empirical understanding of marés’ properties. The study underscores the importance of material-based diagnostics for the sustainable conservation of Gothic heritage architecture.