Porosity as key factor in the durability of two historical building stones: Neapolitan Yellow Tuff and Vicenza Stone

Porosity plays a decisive role in decay processes of stones, as the pore network allows the water penetration responsible for the several physical and chemical deterioration processes affecting stone materials. In this paper two stones (with porosity from high to medium) used in Naples and Vicenza architectures have been considered to investigate the effects produced by the application of an ethyl silicate consolidant and an anti-swelling protective agent on pore space and therefore on stone durability.A deep characterization of the pore system has been carried out as considered crucial to evaluate the effectiveness of conservation treatments and their performance through time. To this purpose, petrophysical and physico-mechanical measurements have been carried out before and after aging tests, on both untreated and treated stones.Conservation treatments, strongly affecting pore size distribution and the behavior towards water absorption, do not always improve the durability of stone, especially in Neapolitan Yellow Tuff (herafter NYT) where a set of meso-macropores was totally annealed as well as a relevant portion of ultramacropores. Such treatments favor the persistence of water in NYT rock structure still after a long time, further contributing to a fast decay of this stone after aging tests. By contrast, treatments in Vicenza Stone (hereafter VS) prevailingly occlude micro- and mesopores and only slightly affect larger pores thus again favoring the flow rate during water desorption test. Moreover, the increase of the average pore radii after treatments also improves the features of this stone that accounts for almost negligible effects after accelerated aging tests.