Effectiveness of Preservative Treatments on Coloured Ruditic Building Stones

Abstract

The dark grey Breccia di Billiemi and the Ammonitico Rosso of Piana degli Albanesi, two coloured stones widely used in monuments both outdoor and indoor in Sicily, undergo significant decay as effect of weathering: colour change and development of surface microcracks which affect not only the chromatic aspect but also the state of aggregation. In a previous study (Fracture and Failure of Natural Building Stones, 2006, Springer, Dordrecht, The Netherlands: 329), such effects were successfully reproduced on laboratory samples by means of artificial accelerated weathering and the different response of veins and grains to the ageing agents was related to the microstructure of stones. In this study, the effect of accelerated washout and acid etching is evaluated both on untreated samples and after the application of four commercial preservative products. The development of decay phenomena is monitored by means of weight measurements and image analysis, coupled with optical microscopy, the last evidencing a selectivity in the effectiveness of treatments on the different textural components of the lithotypes. The effect of treatments on the stones is also investigated by contact angle measurements on different areas.