See AATA 23-3075 for another version of this article which appeared in Czech. The church consists of three naves. While the majority of decorative elements at the outside had already been replaced by copies, the only original part left is an arched frieze with two pillars, each of them with a stone sculpture on its capital (Fig. 1, 1a), at the exterior of the apse of the northern aisle. The whole element is made of cretaceous sandstone (quartz, feldspar, glauconite, chalk), and was already in a bad condition when the National Institute of Restoration, Prague, began the conservation. The restorers were confronted with the fact that a great deal of the frieze's surface had been replaced by a repair mortar during an earlier restoration, the binder of which consisted not only of lime and cement, but obviously also of organosilicon compounds. Moreover, almost the whole frieze had been coated by this material. It was obviousthat the mortar's capacity for water vapor exchange was too low compared to the original stone, resulting in the loss of coherency between them and in a falling off and an exfoliation, respectively, of the repair material, leaving behind a surface with strong granular disaggregation. The technique of long-term dampening by application of water-saturated poultices after some time allowed mechanical removal of the artificial material. The remaining stone surface was then open enough to enable deep penetration of the consolidant. Laboratory examinations on the stone as well as on the mortar were made, including porosimetry (Fig. 4, 5), chemical analyses (Tab. 2), determination of water absorption, microscopy of cross sections, and examination of mechanical strength (Tab. 1). Restoration of the frieze after the removal of the repair filling and the coating was done by consolidation of the stone with siloxanes in an ethanol-acetone 1:1 solution. Penetration of the consolidant to a depth of at least two centimeters was proved before. The application was repeated from 3 to 5 times under conditions of 60-70% relative humidity, without prior addition of water. As a roof shall be fixed protecting the frieze from rain water, no hydrophobization was applied, also with the intent of introducing as few chemicals as possible.