BUGINI, ROBERTO1; FOLLI, LUISA1

1 Istituto CNR Conservazione e Valorizzazione Beni Culturali

via R. Cozzi 53, 20125 MILANO (Italy) – bugini@icvbc.cnr.it

Significant examples of mortared rubble masonry are present in the medieval site of Castrum Sibrium (Western Lombardy, Italy). The masonries were made of horizontal courses of stones, different in size, shape and lithology, together with a mortar to fill the gaps. Three different kinds of stone elements were classified: cobble and split cobble, ashlar, slab. Petrographic techniques allow to identify: igneous rocks (granophyre, andesite), metamorphic rocks (phyllite, schist, gneiss, granulite, green stones) and sedimentary rocks (limestone, dolomite; sandstone, conglomerate). The stones come from loose sediments of different lithology outcropping in the nearby territory and belonging to the deposits of the Ticino glacier (Quaternary). The bedding mortars contain quick-lime with silicate sand and crushed brick as aggregate. The wall-coating plasters contain quick-lime and silicate sand. Different decay phenomena were detected on the masonries, restored since the 1960s: disaggregation of silicate rocks; roughening of sedimentary rocks; detachment of mortars.

Keywords: rubble masonry, glacial deposit, Middle Ages, Lombardy