The Sieve

In order to have a suitable material, it was necessary to sift, sift or sieve the product of the milling, and thus eliminate all the pebbles that might remain raw, known as granza. To do this, the gypsum was sieved in iron sieves or sieves (circular sieves), the holes or meshes of which were of different sizes. This was usually done by hand, individually or between two men.

It was then that the gypsum transformed into powder, that which after undergoing a process of calcination, grinding and sieving of the stone-base material needed the addition of water for its use on site, or, in other words, it had to be rehydrated in order to be used, giving rise to a viscous paste which hardens from a liquid to a solid state, thus recovering the water lost during calcination and returning to its original composition.

Depending on the greater or lesser amount of water, as well as the existence or not of different granulometry and nature, different types of slurries, pastes, mortars and concretes were obtained. Although it should be borne in mind that in most cases the finer aggregate was part of the “characteristics” that accompanied the gypsum at the end of production, as it was sieved manually and sometimes rudimentary, the product did not, of course, have such a regular granulometry as that of modern-day gypsum.