Laboratory testing of mortars for a suitable conservation of mosaics in archaeological sites

The decay of mosaics in archaeological sites depends on different causes (physical, chemical and mechanical), however a relevant role in the conservation of mosaics is related to the composition and structure of the mortars where the tesserae are embedded. These mortars, in fact, may contribute to the release and transport of soluble salts, transport of water and detachment of the tesserae themselves. In this work, on the basis of the problems related to the conservation of mosaics in the archaeological site of villa romana delle Paduline, I-II sec. B.C. (Castiglione della Pescaia - Grosseto - Italy), three different repair mortars useful to embed the tesserae were prepared and their performances tested. In particular the behaviour of these mortars during their preparation, hardening and artificial ageing has been checked. The colour changes of the mortars during hardening and ageing (determined by chromatic test), the water vapour permeability, the cohesion properties (by Drilling Resistance Measurement System) and durability to artificial ageing (thermo-hygrometric changes in presence of water or salt solution uptake) were determined.