Problemy konserwacji obiektów architektonicznych z dolomitu na przykładzie barokowych bram w ogrodzeniu Katedry Wawelskiej

• Authors: Stępień Piotr , Kozłowski Roman , Magiera Janusz

Title variants

EN

Problems of the conservation of dolomitic architectural objects, as illustrated by the case of the Baroque gates of the Wawel Cathedral

• Languages of publication: PL EN

Abstracts

EN

Dolomite has been rarely studied by conservation scientists. The authors’ research has been carried out during the conservation (1992-1993) of three Baroque gates in the wall enclosing the Royal Cathedral at the Wawel Castle, Cracow, Poland. The gates were built between l6l7 and 1619, probably according to the design of an Italian architect Giovanni Battista Trevano from Lugano. Dolomite is the principal material used in these gates. The research has identified in the object several types of dolomite, showing varying resistance to weathering. The mechanism of decay involves acidic corrosion due by sulphur dioxide contained in the polluted air. In contrast to the corrosion of limestone, the corrosion of dolomite yields two reaction products: calcium sulphate (gypsum) and magnesium sulphate (epsomite). Magnesium sulphate is extremely soluble in water. It dissolves and migrates easily in the object and crystallises when the stone dries. Repeated dissolution crystallisation cycles of this salt are the main cause of the decay of dolomite. Symptoms of this decay are deep alveoli, pulverisation and flaking. Furthermore thick black crusts containing gypsum are formed in the non-washed areas. The described process of destruction proceeds differently in different types of dolomite. The porous types and/or those containing many of fine-grained components are much affected. An important damaging factor is exposure to rain water and rising dampness - the corrosion zones in the object are clearly linked to a high moisture content. Conservation of dolomitic architectural objects must involve extraction of soluble salts, specially of magnesium sulphate. Poulticing (cellulose + water) proved an efficient method, but the poultices had to be applied 5-6 times to obtain the reduction of the salt content to levels below 1 weight %. Another important point of the conservation is protection from water. In the case of the gates, new proper roofing of copper leaf and injections at the base of the gate (to obtain insulation against rising damp) were made. The whole surface of the stone was impregnated to obtain water-repellency. A solution of silicone resin (Polish product Ahydrosil Z) was used, both for water-repellency and consolidation. Another possibility is a mixture of acrylic and silicone resins (the method of O. Nonfarmale). Acrylic resins were found insufficiently resistant in Polish climate and silica esters ineffective in the consolidation of relatively large „nodules” of dolomite. It is important also to choose properly the material for repairs, avoiding the „bad” types of dolomite mentioned above. Lime mortars (with some hydraulic additions) and stone powders with a silicone preparation (Adhesil Kl) were used as filling mortars.

• Publisher: Narodowy Instytut Dziedzictwa
• Journal: Ochrona Zabytków
• Year: 1993
• Issue: 4
• Pages: 338-346

Dates

published

1993

Contributors

author

Stępień Piotr

author

Kozłowski Roman

author

Magiera Janusz

References

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Identifiers

ISSN

0029-8247