Selection of a hydrophobic polyurethane material for the restoration of a wayside shrine

A sandstone (Hildesheimer Rhatsandstein) wayside shrine in Algermissen, Germany had to be restored. The stone under the panting required both a strengthening and a hydrophobic treatment and two polyurethane-based products, hydrophobic strengtheners, were considered for this purpose. The aim of the research described in this paper was to select the most appropriate product. For this purpose, measurements on treated anduntreated samples of the sandstone were carried out. Water related properties, such as water uptake and hydric expansion, as well as mechanical properties like flexural bending strength, were measured on both treated and untreated samples. The paper describes the minimalist approach the developed that allowed selecting the suitable product for the conservation of a rather small object with limiting funding.