ABSTRACT
The use of gypsum was fundamental for the installation of Catalan vaults: gypsum is an early set mortar that increases its volume during this phase-instead of decreasing-for the benefit of the contrast among the bricks placed on a flat surface. The first layer was always realised with gypsum mortar and worked as a composite disposable formwork for the upper layers. The latter could be also realised with mortars made with lime and cement and characterised by a less fast set.
