High-temperature gypsum plaster on historic exteriors? A plea for gypsum

In past centuries builders and their clients in regions of Asia, North Africa and Europe with natural gypsum deposits have handed on,the calcining, or "burning", of gypsum from generation to generation, to permit the use of this dehydrated product for their building projects, for building exteriors as well as interiors, and even in high-rainfall districts. In the Orient, this building practice can without doubt be traced back for several millennia. In Germany, the epoch in question lasted from between 850 and 1250 until about 1880 to 1950, varying on a regional basis. There is a great probability that "burnt gypsum" originally invariably signified "high-temperature burnt gypsum", since the high-temperature burning process was known - and mastered from the-burning and firing of lime and bricks. The low-temperature process for production of stucco plaster, on the other hand, necessitated. cauldrons or other vessels, preferably of metal. In view of the fact that burnt gypsum was obliged at all times to compete with other materials, such as slaked lime, hydraulic lime and also common clay, there must have been good reasons for deciding again and again, at,least regionally, in favour of gypsum plaster as an interior and exterior masonry mortar, and as a mortar for exterior rendering. The following article presents, on the basis of many years of extensive observations, seventeen arguments in favour of gypsum plaster, and of high-temperature gypsum plaster, in particular, as a building material. They can be subdivided into process-engineering, logistical, building science, fire-safety, chemico-physical, aesthetic and, of course, subjective arguments.