Durability assessment of differently orientated surfaces of treated long-term weathered natural stones

Abstract

In this study, selected natural stone prisms have been compared with each other to detect the effectiveness of the hydrophobic treatment on differently orientated surfaces. The samples have been examined after 2 and 17 years of weathering at two different locations in Germany. The examinations focused on certain criteria which are based on the research of the last four years. By measuring colour changes, not only the influence of different hydrophobing agents could be investigated, but also different stone deterioration patterns could be identified. It could be determined that the effectiveness of water repellents is significantly influenced by the penetration and distribution depth of the active substance. The results of non-destructive NMR measurements show that the durability of the stones is more influenced by the uniform distribution of the active ingredient and the penetration depth than by the surface orientation. Thus, for the Obernkirchener Sandstone, the efficiency of the applied agents was proven after 17 years of outdoor weathering. Despite determined effective hydrophobic zones, degradation of the natural stones could not be prevented. Measuring the damaged depth with NMR it was found out that water penetrates the stone within the first 500 to 1000 µm, even with an intact hydrophobic layer, and can cause surface changes, like biogenic growth and decomposition. In these degradation processes, the orientation of the samples again has a significant influence. Thus, the roof surfaces show stronger deterioration.