Climate control for the passive conservation of the romanesque painted wooden ceiling in the church of Zillis (Switzerland)

Abstract

Extensive investigations of the deterioration of the romanesque painted wooden ceiling in the church of Saint Martin in Zillis (Switzerland) have revealed three major active deterioration phenomena: (1) tented flaking of paint layers; (2) flaking of the wheat starch fixative together with parts of the paint layer; and (3) fungal growth. These deterioration processes correlate with the dynamics of the prevailing room climate. Both forms of flaking are mainly driven by fluctuations of the relative humidity (RH), whereas the fungal attack can be related to high average RH and stagnant air. Frequent daily fluctuations in RH of up to 20% in summer are due to visitors leaving the doors open, while fluctuations of up to 25% are related to heating in winter. Given the risks of new consolidation treatments, the aim is to slow the decay processes by influencing the climate in the room. Installation of automatic door-closers reduced fluctuations but led to a rise in RH and a reduction of air movement, causing greater fungal growth. Subsequently, an automatic air-exchange system triggered by absolute humidity values was installed to reduce excess humidity and to exchange stale air without producing major fluctuations in the relative humidity. This kind of 'climatisation' has the advantage of being highly flexible, allowing variation of the rate and scale of exchange; it is, moreover, truly reversible.