Zur Dauerhaftigkeit von Hydrophobierungsmaßnahmen auf Naturstein. Vergleichende Fallbeispiele am Kölner Dom und am Ulmer Münster

The long-term durability of impregnation treatments on natural stone cannot be evaluated by means of exact quantitative data. It is difficult to compare different buildings due to numerous factors that determine the durability, in addition to the age of the treatment. Differences in the material and in its alteration due to weathering as well as differences in the emission rate, exposure, and shape of the building part are important parameters. Moreover, the kind of agent used, the method of application, and the carefulness of the restorer can determine the durability. At Cologne Cathedral and Ulm Minster impregnated test areas were investigated a second time at a time interval of five and six years. The results confirm earlier investigations and show remarkable differences with respect to the exposition and the waterproofing agents used. Mechanisms reducing efficiency are discussed.