The studied limestone is a well known Portuguese natural stone that occurs in Valverde – Alcanede region, located in the Maciço Calcário Estremenho (centre of Portugal). This stone is used in several exterior and interior applications such as paving, cladding, masonry and decorations. Slabs made of the studied limestone were installed in ventilated facade with a “kerf” anchoring system in a building located in Valencia (Spain). After approximately five years, signs of degradation were detected on the facades through changes in color, cracks and fissures that caused instability and collapse on several slabs. Limestone slabs comprise irregular patterns due to rock cutting across stylolites. These features represent ideal paths for fluid circulation through the slab and can be identify as vulnerability zones for exterior applications. Experimental procedure included several laboratory analyses in order to study clays and the iron oxide contents. Microscopic petrography, XRD and SEM observations were important to identify the interaction of the clay material in stylolites and fossil contours. Results show the importance of establishing standard methods for selecting stone on cladding applications. From the results, it is possible to understand that clay minerals have a strong influence on the mechanical performance of this stone. Among other important remarks, results show the importance of the development of standard procedures that acknowledge the structure and mineral composition before setting these natural products as construction materials. Proper stone selection was found important to avoid facade degradation, and hence contribute to prevent accidents and promote user safety as well as economic impacts.