Analysis of Moisture for the Preservation of Frescoes at Malpaga Castle

The preservation planning of frescoes requires a precise knowledge about the building technique of the masonry, the microclimatic conditions inside the rooms, its variations due to the changes of the weather in addition to the measures of moisture and the map of its distribution. The case study presented in the paper regards the ancient castle of Malpaga, which is settled near Bergamo, Northern Italy. The building was begun in 14° century, and it was accomplished in 15° century by Bartolomeo Colleoni. Three layers of frescoes decorate the whole surfaces. Objectives of the analysis are the identification of the risk areas, because of the damage already visible and the microclimatic anomalous conditions, and the verification of the hypothesis about the causes of the moisture. Only NDT may be applied, because of the preciousness of the surfaces. The measures were repeated at different weather conditions and in the same days at different hours. The results revealed that the orientation, the disposition of the rooms, the number and wideness of the openings, contribute to modify the temperature of the air inside during the day, decreasing the threshold of dew in few hours and, above all, many times in a short period. The other measured variables are due to the differences of the thickness of the masonry and its component. The tests allowed to map the colder areas, where dew can condense, and the zones affected by rising damp. The results allowed to design the specific air-conditioning plan and those minimal interventions to decrease the effects of the air streams nearby the surfaces of the frescoes.