Deterioration and preservation of Carolingian and mediaeval mural paintings in the Müstair Convent (Switzerland) Part I: Decay mechanisms and preservation

Abstract

1 THE PROBLEM Since the wall paintings were restored in 1947-51 accelerated decay has been observed. Three types of deterioration occur: 1 deposition of dirt, 2 detachment of the Romanesque intonaco from its support, 3 decay produced by soluble salts. In order to understand the entire problem, some general features and the main events which have affected the paintings will be mentioned. The Miistair Convent is situated on an alluvial cone at 1250 meters above sea level, in the Miinstertal,a valley issuing to northern Italy at the southeastern border of Switzerland. The alluvial coneis used as farming land. The church is integrated into the building complex of the convent and its southern and eastern side lie next to a public cemetery. The walls, composed of local rubble stones (schists, gneisses and rauhwackes) and lime mortars, still carry the original mediaeval lime plaster on their outside. Only in the basal zones, where they were affected by ground moisture, the plaster has been replaced by mortars containing Portland cement. The walls of the convent show the normal aspect of rising damp up to some three-four meters above the soil. The inner surface of the church is covered by the Carolingian plasters and frescoes, on which the Romanesque ones with their intonaco are superposed. Actually the preserved portions of the Carolingian frescoes are visible on all walls with the exception of the three apses, where the well-preserved Romanesque. paintings are partially superposed. The. main events that have affected the mural paintings are given in Table 1. The most remarkable events are two fires in the eleventh and fifteenth centuries, and the last restoration of