Historical plasterwork techniques inspire new formulations

Gypsum based mixes for conservation purposes: evaluation of microstructural and mechanical features

“…1. pure gypsum as a reference; 2. gypsum plus rabbit glue (11,33); 3. gypsum plus MgO (33); 4. gypsum plus lime putty (11,16,33,41,42) The amount of water was considered crucial to achieve the final performances, so its weight in each mixture was measured.…”

“…It is known from the literature that magnesium could be present in lime mortars, when magnesian lime is fired in the kiln (43,44) starting from rock raw materials with dolomite impurities (4). Lime putty was selected because, when mixed with gypsum, it forms a well-known and diffused blend utilised in stuccoes practice (11,13,33,38,41). Finally, the choice of the rabbit glue is due to the well-documented use in scagliola and pastiglia techniques, for example in the creation of altar frontals (11,15,41).…”

“…Lime putty was selected because, when mixed with gypsum, it forms a well-known and diffused blend utilised in stuccoes practice (11,13,33,38,41). Finally, the choice of the rabbit glue is due to the well-documented use in scagliola and pastiglia techniques, for example in the creation of altar frontals (11,15,41). It is worthwhile to note that magnesium oxide and calcium carbonate have been detected in recent characterisation studies (9,11,13,28,45), as well as animal glue or other protein based materials (11,41).…”

“…Choices in stuccoworks making, for example low and high reliefs, mouldings and in the round statues implied the workability properties of the mixes used. For these reasons gypsum was often mixed with both organic and inorganic natural and artificial materials, such as lime putty and organic additives (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). The blend with animal glue and pigments was widely used in painting ground layers and in gilded artworks, especially in the south of Europe (21)(22)(23).…”

19th c. Coloured stuccos and plasters from Grilos' Church (Oporto, Portugal): Materials and techniques employed

“…(a) and (b)]. The addition of lime water, used as a wash, in the gypsum based mixture, harden the surface of setting stuff, improves moister resistance, and retards the setting, useful for molding directly the plaster. In the plasterwork of the Church's nave, the plane plastering is applied in a single gypsum‐based mortar layer on the granitic wall because of the following factors: the granitic ashlars present quite straight and rugous surface that is adequate for the good adherence of a single plaster layer; the low porosity of the granite, when well wetted does not lose the water quickly, and so, when plain plastering is applied, it keeps the humidity during the time necessary to execute the decorative plastering.…”