Were Castle Walls in Portugal covered with Renders? - The case of Arraiolos Castle

Abstract

Arraiolos Castle is one of the medieval fortresses that still stands in Southern Portugal with few modifications of restoration and preservation interventions. Particularly relevant is the fact that large areas of the castle walls are covered with mortars and some have gothic inscriptions that point out to their production in the second half of the 14th century. This work was carried out in order to verify if the mortars present were the same with each other and with the age of the mortar inscriptions. The characterization methodology involved a multidisciplinary set of chemical and microanalytical techniques, as well as radiocarbon dating. The results showed that all render mortars have similar composition, with aerial calcium magnesium lime as binder and aggregates with siliceous nature and similar in composition to the rock of the region around Arraiolos. The radiocarbon blind analysis corroborated the date discovered in one of the gothic inscriptions found in the renders of the castle walls.