Cappadocian ignimbrite cave churches: stone degradation and conservation strategies

The focus of this research is to investigate the minero-petrographic features and theconservation aspects of the stone materials from some rock-hewn churches in Cappadociaregion (Turkey) in order to choose the most appropriate consolidating systems to improve theresistance against the weathering and degradation phenomena of this unique world heritagesite. In this study, specimens from the Tokalı church in the Göreme’s Open Air Museum, andfrom the Forty Martyrs Church in Şahinefendi were analysed by optical microscopy and Xraydiffraction in order to examine the properties of the rock and especially how well preservedit is. The ignimbrite samples show a porphyritic structure with vitrophyric groundmass andcrystalloclastic-vitrophyric texture. The presence of smectite and illite caused serious damageto the rock structure such as cracks, decohesion, exfoliation, and disaggregation phenomena.The consolidation tests were performed on the ignimbrite specimens, sized according tothe standard procedure, by using three commercial silica-based products: NanoEstel, Estel1000, and Estel 1100. The consolidant penetration was investigated by titanium labellingprocedure 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 stonesurfaces before and after the consolidating treatments. Lastly, the surface cohesion due to theconsolidation was investigated by using the peeling test carried out on untreated and treatedsamples.The consolidating tests showed that the solvent-based products (Estel 1000, Estel1100) exhibit a better distribution than the aqueous suspensions (NanoEstel). NeverthelessNanoEstel gives better results in the capillary absorption test, suggesting that this product hasthe ability to leave the stone porous structure substantially unaltered.