Stucco Marble in the Dukes Chapel in Krzeszów, Poland - Microclimate and Degradation Mechanisms / Stuckmarmor in der Fürstenkapelle in Krzeszów (Grüssau) Polen- Mikroklima und zerstörende Mechanismen

The baroque Dukes Chapel in Krzeszów, Poland, contains elaborate stucco marble decorations of great historic value and artistic quality. Cracks and losses appeared in the thin stucco marble layers as a result of layer deformation and detachment from the ground. The glossy polished surface has become locally eroded and rough, and the original material deformed and porous. The damages are located in a non-uniform way; they appear at the base of the walls and high on the vaulted ceilings. A year-long monitoring of air parameters has been conducted inside and outside the chapel. The micro climate of the chapel has been found to be strongly influenced by the outside climate via air exchange with the exterior. The unheated interior undergoes cooling during the winter period and warms up very gradually during the spring and summer. This thermal inertia of the building gives rise to periods of moisture condensation on the walls. Large amounts of magnesium sulphate, which leached out in the past from the dolomitic mortar, are present in the deteriorated decorations of the ceiling. The repeated periods of moisture condensation and evaporation lead to the damaging cyclic crystallization of the salt. Considerable swelling of the stucco marble on humidification is another cause of the deterioration observed. The conservation strategy should restrict the air exchange between the chapel and the exterior and include treatments removing magnesium sulphate from the material.