Most of the Provence built heritage was erected using a material commonly named " Pierre du Midi ". The exposure of these limestones to natural weathering leads to specific deterioration patterns. Among these, spalling tends to develop in areas apart from capillary rise as well as free from soluble salts, air pollution or biological colonization. The origin of this phenomenon remains uncertain. However, it seems induced by the intrinsic properties of the material and its behavior with respect to water content variations. The present study was aimed to understand the mechanisms and specifically to establish the role played by the clay minerals. From the informations collected in the field, a wide variability of spalling degree has been highlighted on historical buildings of equivalent construction periods. This variability is to be linked with the type of "Pierre du Midi" considered. A representative sampling of the different limestones types has thus been realized. A conventional study on the petrographic characteristics and the mineralogical composition has first been conducted. Then, the clay minerals assemblage of each sample has been defined thanks to an adapted methodological approach combining TEM-EDX characterization to XRD profile modeling. This method allowed determining both the nature and the quantity of each clay mineral phase. Beneficiating from the results, the link between the expansive layers quantity and the spalling degree has been evidenced. The storage and transport properties of the different types of limestones were also defined. Moreover, the macroscopic behavior upon water content variation was assessed through dilation and compressive strength experiences. All of these properties highlight the heterogeneity of the studied material. The durability index calculated from these results fail however to predict the spalling degree. A statistical analysis of the experimental data was thus necessary to understand the relative influence of each parameter. The reading of the results suggests that the mechanism leading to spalling decay is triggered by the interaction between the expansive clay mineral layers and the water molecules. The hydromechanic behavior of the stone constitutes the macroscopic symptom of this interaction. This behavior is highly controlled by the fluid storage and transport properties that condition the macroscopic transmission of the deformation created by the swelling occurring at the nanoscopic scale.
