Restoration of the Baroque Plague Column, Kutná Hora, Czech Republic

Abstract

The Baroque plague column in the historic centre of Kutná Hora (UNESCO World Heritage site), has undergone several unsuitable repairs throughout its history, leading to the acceleration of degradation processes. The main issues associated with past restoration efforts included extensive fillings made of Portland cement and epoxy resins, as well as incompatible strengthening methods. These, combined with massive black crusts and the presence of water-soluble salts, caused significant damage to the stone. This paper primarily focuses on the thorough preparation for restoration, including a detailed examination that uncovered remnants of historic polychromy. A key part of the process was the restoration of a sample area involving the testing of suitable technologies and materials, including cleaning methods, verification of stone consolidation options, and the selection of appropriate materials for filling. The paper also describes the restoration work itself, during which the heavily soiled surface was cleaned using a combination of Q-switched laser and micro-sandblasting. Material degradation was addressed through deep consolidation using organosilicon compounds and lime nanosuspensions. The intervention also included ongoing desalination using wraps and the prevention of water ingress into the monument. Laboratory testing led to the development of an optimal composition for fillers, based on hydraulic lime combined with limestone aggregates. The restoration work also involved securing the remnants of the original polychromy. An important part of the paper is the evaluation of the restoration work after five years, as well as an assessment of the applied technologies and maintenance regime.