Abstract
The conservation of buildings in the Basque Country made of Eocene sandstone is somewhat problematical, because this type of rock is relatively unstable. This instability is due to the variable content of carbonate cement (0-28%) and the presence of K-feldspar grains (1-13%) which appear to have been dissolved by both diagenetic and environmental processes. We have compared the results of the application of two commercial consolidating products: Sicof SM 296 (product A) and Consistone FS-hA (product B), both ethylsilicates, on Eocene sandstones of the Oquendo Admiral House (16th century) and the Gipuzkoa Provincial Government Palace (19th century), which are both located in the city of San Sebastian (Province of Gipuzkoa, Basque Country, Northern Spain). On the basis of different chemical and physical laboratory tests, together with Scanning Electron Microscopy (SEM) analysis, product A seems to be more efficient in consolidating such Eocene sandstone materials, since it penetrates into the first 8 mm of the rock, occupies very homogeneously even the smallest pore spaces and leaves a certain degree of remaining porosity which allows ventilation of the rock. In contrast, product B seems to be more appropriate for larger pore-sized rocks, because it only penetrates into the first 3 mm of the Eocene sandstone samples due to the thin pores of the matter. Our results demonstrate that the suitability of a commercial product depends not only on its own chemical composition, but also on the textural and lithological features of the rock material upon which it is to be applied.
Highlights
Over the last few decades, it has been worry i n^^ to observe directly the rapid course of the deterioration of the external façades of a number of historical buildini^s in the Basque Country
The measured dijfractograms of Oquendo Admiral House (OAH) samples show that the Eocene sandstone is mainly made up of quartz (Qz), muscovite (Mcv), alkali feldspar (Fd), illite and sometimes calcite (Ca) (Figure 6a)
The Gipuzkoa Provincial Government Palace (GPGP) sandstone is composed of quartz, alkali feldspar, illite and occasional kaolinite and chlorite, together with traces of gypsum (Figure 6b)
Summary
Over the last few decades, it has been worry i n^^ to observe directly the rapid course of the deterioration of the external façades of a number of historical buildini^s in the Basque Country. The causes for this can be found in dissolution processes which have affected the natural cements of the rock and, to a lesser extent, in vci^etal settlini^ on the external surface of the rock. The northern, eastern and western façades were made of a rubblework of much more resistant lithology, such as sandstone from the so-called Supraurgonian Complex (middle Cretaceous)
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