Examples of weathering and deterioration of Tertiary building stones at St. Michaels Cathedral in Cluj-Napoca (Romania)

Abstract

St. Michael's Church is one of the oldest Gothic architectural monuments in Cluj, Romania, being built predominantly from Cenozoic (Eocene) limestones, locally known as the Cluj Limestone. These limestones are composed of different facies and microfacies types and were deposited on a shallow carbonate platform. The weathering features correspond to the microfacies types, to the position of the stones in the walls, and to the exposure (E, S, W, and N), which controls the moisture/dry cycles. This interrelationship is documented by macroscopic and microscopic examples of the decay of samples from the lower part of the walls. The general mechanisms of weathering, the migration of moisture, and the formation of crusts of varying mineralogy on the surface of building stones are documented. The macroscopic description of damage includes the decay into plates and flakes, the formation of crusts, the formation of fractures, and the growth of lichens and microorganisms. The microscopic analysis documents characteristic damage in detail: fractures parallel to the surface of the stone, internal cementation of fossil chambers, repeated formation of crusts in varying generations, fracturing in intensively lithified, rigid limestones, and settling of lichens in different positions. Briefly discussed are the behavior of the historical mortars and modern "concrete-mortars" in comparison to the adjacent limestones. Techniques of preservation and restoration are discussed with regards to the most recent methods used. The advantages and disadvantages of surface preservation by silica ester, by hydrophobic substances and by epoxy resin, as well as, acrylic total impregnation, lime slurry, biological lime slurry, and DIN-methods are presented.