Determination of the impregnation depth of siloxanes and ethylsilicates in porous material by neutron radiography

For conservation of the built cultural heritage, the application of conservation products like consolidants or water repellents is often suggested. Their impregnation depth is a key factor for the assessment of the treatment efficiency. It will vary depending on the internal structure of the stone material and the properties of the conservation products. In this study a porous bioclastic limestone from Maastricht (the Netherlands) and a porous sandstone of Bray (Belgium) were selected for treatment with either ethylsilicate-based consolidant products or siloxane-based water repellents. We explore the potential of neutron radiography to visualize the conservation products after polymerization, since previous experiments already proved their detectability before polymerization. Additionally, water absorption by capillarity was monitored inside the samples. The experiments in this study illustrate that the ethylsilicate-based consolidants remained visible for neutrons even after the polymerization process, while the siloxane-based water repellents can only clearly be distinguished in the stone as long as they contain a certain amount of solvent. The study proves that neutron radiography can provide important additional information for the research in the built cultural heritage domain, especially as it allows to successfully visualize the impregnation depth of silicate-based consolidants inside natural building stones.