Weathering of marble and calcareous breccia in the lateral facade of Foligno cathedral: influence of lithology and role of exposure

The influence of lithology and exposure in weathering were investigated in two very different building stones. a medium-grained Carrara marble and a calcareous breccia from the lateral facade of Foligno cathedral. Weathering of marble is significantly influenced by the grain size and by the additional porosity induced by thermal 'cooking'. Breccia, instead, shows two distinctive behaviours to weathering depending on its state of aggregation: in fact the well recemented material is resistant to weathering and its behaviour may be assimilated to that of its constituent clasts, whereas the poor-recemented material may be variably resistant to weathering depending on the extent of macropores present However, the calcareous breccia as a whole exhibits a higher durability than marble at the environmental conditions, as it is less involved in the dissolution attack of its calcitic cement at large scale, and more resistant to sulfation at small scale. Exposure plays an important role in the development and diversification of the crusts and deposits through the extent of sheltering of the surfaces, as black crusts result from dirt washing, whereas superficial deposits are related to dirt accumulation of pollutants.