The use of whole gypsum plasters, i.e. made of gypsum binder and coarse selenite aggregate, still can be found in several historic buildings in Italy (both monumental and rural), but it is absent in historical architectural treatises and totally neglected in current restoration works. The main features of these plasters include good mechanical properties and good resistance, even to outdoor environments, despite their gypsum-based composition; thus, they appear worthy of conservation. In this paper, several specimens of such plasters collected from historical buildings are characterized for the assessment of their formulation, microstructure and state of conservation, as a contribution to the preservation of this interesting technological legacy.