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Features of solutions based on high-strength gypsum

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26.06.2013
Gypsum world news

A distinctive feature of gypsum mortars based on dry mixes in comparison with cement mortars of a similar purpose is a reduced material consumption, which makes it possible to obtain a 2-fold larger area from the same mass of gypsum-based dry mix than on cement-based dry mixes. In addition, the use of gypsum dry mixes for finishing reduces labor costs by more than 2 times compared to cement mortars.

It should be noted that the technical properties of gypsum mortars depend mainly on the quality of the gypsum binder, since its content in dry mixes is 70-90%, while the proportion of filler is small. Therefore, when developing recipes for dry building mixes based on gypsum binder, its careful input control is necessary. For gypsum binders, it is necessary to control the setting time, fineness of grinding, brand, and humidity. According to GOST 125, there are three types of gypsum according to the fineness of grinding (I, II, III), which are evaluated by the remainder on a sieve with a grid number 02. At the same time, even in finely ground gypsum (III), no more than 2% of particles with dimensions of more than 200 microns are allowed.

The brand of gypsum binders based on semi-aqueous modifications of calcium sulfate according to GOST 125 is tested after 2 hours of air hardening. For manufacturers of dry gypsum mixes working on commercial gypsum, it is necessary to control the humidity of the gypsum binder. It is established that depending on the humidity of the air during storage of the binder from 65% to 98% rel. after 7 days, the humidity of gypsum is 0.8 and 14.0%, respectively. At the same time, it is not possible to provide the required information according to SNIP 28013-93 "Construction solutions. General technical conditions " humidity of dry mixes is less than 0.1%.

The final moisture content of gypsum dry mixes is in the range of 0.7-0.8%. At the same time, it should be taken into account that an increase in humidity affects the change in the setting time and water demand of gypsum. According to VNIISTROM, gypsum dry mixes with a moisture content of 0.7 - 0.8% retain their original properties for six months of storage. However, it is necessary to periodically check the properties of dry mixes to predict the quality of solutions on gypsum binders.

Currently, the following types of dry gypsum mixes are produced::

  • plaster mixes (including light ones)
  • putty mixes
  • grout mixes
  • gypsum glue
  • drywall adhesive
  • self-levelling floor mixes.

Location:

Samara, Russia
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