Bowing of Carrara marble slabs used as cladding was observed in a seventeen years old, 7-story commercial building, located in the southern part of Switzerland, and exposed to temperate climatic conditions. In this paper we will report on the results obtained in a laboratory investigation conducted with a twofold aim: the evaluation of the condition of the weathered slabs, on the one side, and the comparison between the effects of natural and artificial weathering, on the other side. A marble slab removed from the façade cladding and a reference slab of unweathered marble, were used to prepare several testing specimens. Flexural and compressive strength and their related elastic moduli, transversal tensile strength, unit weight and porosity parameters, were determined on specimens taken from both slabs. In addition, their microstructures were examined using optical and fluorescence microscopy. The comparison between the results obtained on both sets of specimens show an important reduction of all the measured mechanical properties and a significant increase of the porosity in the weathered slab. Observations made with the microscope clearly show that the bowing of the slabs is related to a widening of the straight grain boundaries, resulting in a kind of microfractures network. Furthermore, weathered and unweathered samples were submitted to 50, 100 and 200 cycles of artificial weathering. Each cycle included the exposure of the specimens successively to periods of rain, freeze (-16°C) and irradiation by a xenon lamp (65°C). Flexural strength and its related elasticity modulus were measured and the microstructures were observed under the optical microscope. The naturally weathered specimens show higher elastic modulus and lower flexural strength than the specimens exposed to 200 cycles of accelerated weathering. The more significant changes occur already after the first 50 cycles.