Lime-based Sacrificial Layers – Evaluation of a Traditional Conservation Method Applied in an Urban Environment

The use of modified lime slurry as a sacrificial layer to protect the original porous substrate has a long tradition in the practice of building and monument conservation in Austria. This paper presents the results of analyses performed on the Natural History Museum Vienna to get more insight into the long-term performance of this conservation method. Stone surfaces on the facade and roof area, covered with an acrylic tempered lime sacrificial layer and subsequently made water-repellent, were tested in situ and in the laboratory. Whilst coatings in the exposed zones were completely vanished in certain areas, the samples from the facade were in a good condition even after nearly twenty years of exposure. Hydrophobic activity could be verified up to a depth of five mm in the porous stone substrates. Despite the general good state of preservation of most surfaces, the existence of highly hydrophobic substrates will definitely restrict the implementation of any future sustainable conservation effort.