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

Abstract

The Oporto’s St. Lourenc¸o Church of the JesuitCollege is locally known, since the St. Augustin BarefootedEremites occupation (1779/80), as Grilos’ Church. TheOporto’s siege laid by D. Pedro and D. Miguel (1832/33)succeed in the college abandonment by Grilo’s Friars.Throughout Augustin Friars presence period, the whiteplasters of the nave (end of 18th c.) were executed and itwas constructed the Holly Sacrament Chapel (early 19thc.) with neoclassic coloured stuccos and plasters, influ-enced by Robert Adam, Luigi Chiari and Teixeira Barretoornamental motifs. Pigments were added to the externallayer to imitate the marble and to achieve the “base” col-our of the panels. This study of the blue, rose and whitestuccos and plasters of H.S. Chapel of Grilo’s Churchallows carrying out useful database on the original mor-tars composition by the use of different analytical techni-ques, important to select the most adequate solutions forrestoration interventions. Optical microscopy, XRD, TG-DTA, SEM-EDS, XRF analysis results were considered toidentify the composition of different layers and to providemineralogical, microstructure and chemical characteriza-tion of the mortars components and to quantify the bindercontent in those mortars. These results were comparedwith collected information on compositions from othersources. This study allowed the identification of the decaycauses of decorative stuccos and plaster, suggesting thatwater retention in the masonries and wooden laths struc-ture of the dome of the chapel is the main factor