Preliminary communication
https://doi.org/10.17018/portal.2025.16
Stone of Zagreb Cathedral: History of Decay and Interventions
Vinka Marinković
; Croatian Conservation Institute (Split)
Edita Šurina
; Croatian Conservation Institute (Zagreb)
Abstract
In the series of earthquakes that struck Zagreb in 2020, one of the city’s most significant historical buildings, Zagreb Cathedral, suffered severe damage. This unfortunate event provided an opportunity in the subsequent years, during preparatory work for its structural repair and comprehensive restoration (2022–2023), to consolidate knowledge about the cathedral’s stone materials.
This paper offers a brief overview and analysis of the technical properties of the stone used in the cathedral’s construction: lithothamnium limestone (litavac) and calcareous sandstone. It also outlines the history of work and intervention on the cathedral’s stone facades, with a focus on the period from 1937 to 2020, during which heavily-damaged stone was largely replaced. This section examines in detail the historically documented problem of the original stone’s degradation, primarily the transformation of calcite (calcium carbonate, CaCO3) into gypsum, leading to gypsum swelling, stone disintegration through spalling and flaking, and the circumstances surrounding the choice of travertine as a replacement stone during exterior renovations.
The condition of the stonework and carved stone elements after 2020 is described with emphasis on, and a catalogued overview of, internal areas. In addition to earthquake damage from 2020, characteristic damage and accumulated contamination over time have been identified. Almost all the stone facades of the cathedral, and most carved stone elements inside, bear multiple historical layers of coatings and finishes, rendering the original stone structure largely unreadable, and making problem-detection challenging. It was determined that the issues inside are similar to those on the exterior, including extensive flaking and spalling, loss of surface layers, porosity and significant joint damage. Moisture and associated issues, such as the presence and crystallization of water-soluble salts, also pose challenges.
The following section discusses newly documented elements of final detailing (documented between 2022 and 2023): masons’ marks, graffiti and inscriptions, coats of arms and ribbed vault profiles. All documented elements are accompanied by photographs and/or drawings. Their documentation during these investigations, as well as their recording in forthcoming conservation and restoration, will contribute to a more detailed understanding of specific alterations and the historical sequence of events at the cathedral.
The final section presents a general proposal for conservation and restoration of the stone elements inside the cathedral, along with guidelines for further work on the exterior. A detailed conservation and restoration approach is recommended, differentiated by the types of damage and contamination between the interior and exterior. For the exterior, additional guidelines are specified, including the designation of zones requiring special conservation and restoration treatment, coordination of past work and approaches, and cataloguing of all components ever removed from the cathedral. During the execution, the emphasis is on the conservation and restoration of stone, with the replacement of blocks and carved details to be carried out only when structurally necessary.
Keywords
Zagreb Cathedral; conservation and restoration; stone consolidation; limestone; sandstone; travertine; masons’ marks; graffiti and inscriptions; coats of arms; ribbed vault profiles
Hrčak ID:
342562
URI
Publication date:
15.12.2025.
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