You may remember that gypsum binders are building binders obtained by calcining and grinding gypsum dihydrate contained in sedimentary rocks.
Depending on the processing temperature, the binders are divided into two broad categories: soft-burnt and hard-burnt binders. Hard-burnt gypsum binders are the so-called anhydrite cement and estrich gypsum plaster — hard-burnt gypsum proper. Soft-burnt gypsum binders are molding and high-strength construction gypsum plasters.
Let us give a more detailed classification of gypsum binders. As a rule, all types are divided into 12 grades according to their maximum strength:
| Grade: | : Maximum flexural strength, MPA, NLT |
|---|---|
| G-2 | 1.2 |
| G-3 | 1.8 |
| G-4 | 2 |
| G-5 | 2.5 |
| G-6 | 2.5 |
| G-7 | 3.5 |
| G-10 | 4.5 |
| G-13 | 5.5 |
| G-16 | 6 |
| G-19 | 6.5 |
| G-22 | 7 |
| G-25 | 8 |
Depending on the setting time, gypsum binders are divided into fast-hardening (initial setting time - 2 minutes, final setting time - 15 minutes), standard hardening (initial setting time - 6 minutes, final setting time - 30 minutes) and slow-hardening (initial setting time - 20 minutes, final setting time- not standardized). According to the grinding fineness, gypsum binders are divided into compositions with coarse, medium and fine grinding.
Gypsum-based binders are used as an independent bulk material in a dry mortar mix or added to compositions with other base binders — for example, to lime-sand mortars to increase their strength and accelerate setting. Adding gypsum binders to plaster mortar improves smoothness and whiteness of the surface. The most common component of dry mortar mixes and products is grade G-2–G-7 gypsum plaster. During manufacture of products, gypsum binders are mixed not only with water, but also with polymer dispersions. This allows obtaining polymer gypsum plaster which is significantly superior to conventional gypsum plaster in many aspects: density, strength (up to 30 MPa), water resistance, volume stability, abrasion resistance, and electrical insulating properties.
Packaged gypsum-based binders are transported in covered goods wagons and cars and stored in rooms that are reliably protected from moisture. With prolonged storage, even under normal conditions, the activity of gypsum binders decreases.