Il pavimento del Duomo di Siena. Valutazione critica dei danni provocati dall’attuale sistema di protezione

The paper reports a study of the flooring of the Cathedral of Siena (Italy).This is a unique work of great beauty, consisting of innumerable marble decorations, which was created during the period 1369 to the first half of the 16" century. This study, which included also an architectural survey of the flooring, looks at physical and chemical deterioration processes arising from the current floor protection, which consists of a covering made of panels of faesite. Various analyses, including mineralogical, chemical and SEM studies, have shown that these panels, which are impermeable and acidic, in conjunction with high, persistent humidity, have resulted in the creation of a micro-environment at the interface with the flooring, which is very aggressive towards carbonate lithotypes. Soluble salts (sulphates, chlorides, nitrates), which contribute towards deterioration of the stone, are thus mobilised and transported. The most obvious result of the corrosive effect of these panel is the formation of a “shadow" on the panels, which effect is visible when they are removed from the flooring.