PLUL

Ultracal 30 is a gypsum cement made for patternmaking, where the measurements of a model are the thing being delivered. It holds its dimensions closely and stays workable for a good while after mixing.

Ultracal 30 moves very little between the wet pour and the finished piece, which is what patternmaking asks of a material and why it goes into master models, block-and-case work, dies, and the rigid jackets that back a flexible mould. In all of those, any growth on setting would be inherited by everything cast from the piece afterwards. It also stays workable for a good while after mixing, so a jacket or a case can be laid up over a model without racing the set. The setting is a chemical reaction rather than a drying: the powder takes water back on and grows interlocking crystals, and the mix warms as that runs.