Gypsum is one of the oldest building materials. Under natural conditions, it is found as crystalline calcium sulfate salt with two water molecules . After appropriate treatment – chopping , grinding and roasting – gypsum becomes viscous material . After contact with the appropriate amount of water required for the bonding process , it returns to its original shape. After drying of the plaster is resistant to compression and is relatively easy . Worse is its tensile characteristics . All its mechanical properties deteriorate when wet.
Thanks to its unique qualities , gypsum has the ability to adjust the relative humidity : it quickly absorbs moisture and quickly compared with other materials , dries , giving moisture to the surrounding air . With this premise , built using plaster, have a distinctive microclimate in which a person feels fine .
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Modern chemistry is capable of , changing the structure of the material , they reduce the absorption of water, but then much more expensive product .
Other gypsum role associated with the presence within its structure of two molecules of water, is that on one hand the gypsum element in direct contact with the fire , can keep the temperature for a long time of about 120 * C, another duration of this effect depends on the thickness of the plaster layer and the intensity of the fire. This property plaster making it one of the cheapest fireproof materials.