The application of geopolymers in the renovation of the historical ceramic tiles in the pilgrimage church of St. John of Nepomuk (Czech Republic)

This article describes the use of geopolymer materials for the renovation of historical ceramic tiles from the mosaic floor of the church of St. John of Nepomuk. The restoration project, carried out in close cooperation with expert restorers, proceeded in several stages. These stages included initial experiments to assess the suitability of the geopolymer material, the development and adjustment of the geopolymer composition, the possibility of coloring the mixture, and extensive testing to evaluate the effect of ambient temperature on the geopolymer setting. Experiments with different geopolymer mixtures have shown that higher slag content can reduce the setting time but it also changes the consistency, color and surface hardness of the material, which are crucial properties for restorers. Finally, suitable geopolymer mixtures were created to meet the specific requirements of restorers. The project involved the successful bonding and reinforcement of damaged tiles in a controlled laboratory environment. The restoration process was concluded with an in-situ application – filling in the missing parts of the ceramic tiles in the church. This comprehensive approach highlights the potential of tailored geopolymer materials in the protection of cultural heritage.