Gypsum coatings in ancient buildings

Gypsum plasters from old buildings are a legacy of the building techniques of our ancestors. These coatings, frequently gifted with a high artistic value, are part of the historical building heritage of each country that needs to be well known and preserved.The present paper begins with a general overview of the history of gypsum plasters in Portugal, since the most ancient traces in the Roman period until modern plasters.A description of the main coats that constitute traditional gypsum plasters follows: the lime mortar undercoat, the lime, gypsum and fine sand preparation coat with a thickness of 3–5 mm and the gypsum finishing coat, made of gypsum and air lime slurry.Next, the constitution of the backgrounds is described, namely of the timber framed main walls and of the partition walls typical of the anti-seismic Pombalina construction used in Lisbon after the 1755 earthquake. Finally, the constitutions of the several plaster coats and their production and application process are referred to.