Cappadocian ignimbrite cave churches: stone degradation and conservation strategies

Abstract

The focus of this research is to investigate the minero-petrographic features and the conservation aspects of the stone materials from some rock-hewn churches in Cappadocia region (Turkey) in order to choose the most appropriate consolidating systems to improve the resistance against the weathering and degradation phenomena of this unique world heritage site. In this study, specimens from the Tokali church in the Göreme's Open Air Museum, and from the Forty Martyrs Church in Şahinefendi were analysed by optical microscopy and Xray diffraction in order to examine the properties of the rock and especially how well preserved it is. The ignimbrite samples show a porphyritic structure with vitrophyric groundmass and crystalloclastic-vitrophyric texture. The presence of smectite and illite caused serious damage to the rock structure such as cracks, decohesion, exfoliation, and disaggregation phenomena. The consolidation tests were performed on the ignimbrite specimens, sized according to the standard procedure, by using three commercial silica-based products: NanoEstel, Estel 1000, and Estel 1100. The consolidant penetration was investigated by titanium labelling procedure followed by scanning electron microscopy-energy dispersive spectroscopy analysis. Colour measurements were used to study the possible chromatic changes due to the treatments. The capillary test was performed to evaluate the amount of water absorbed by the stone surfaces before and after the consolidating treatments. Lastly, the surface cohesion due to the consolidation was investigated by using the peeling test carried out on untreated and treated samples.The consolidating tests showed that the solvent-based products (Estel 1000, Estel 1100) exhibit a better distribution than the aqueous suspensions (NanoEstel). Nevertheless NanoEstel gives better results in the capillary absorption test, suggesting that this product has the ability to leave the stone porous structure substantially unaltered.