4. Water retaining agent
Gypsum dry-mix building materials are inseparable from water-retaining agents. To improve the water retention rate of gypsum product slurry is to ensure that water can exist in gypsum slurry for a long time. In this way, a good hydration hardening effect is obtained.
Improve the constructability of gypsum powder building materials, reduce and prevent segregation and bleeding of gypsum slurry. Improving the sagging properties of slurry, prolonging the opening time, and solving engineering quality problems such as cracking and hollowing are all inseparable from water-retaining agents.
Whether the water retaining agent is ideal mainly depends on its dispersibility, instant solubility, moldability, thermal stability and thickening property. One of the most important indicators is water retention.
There are four types of water retaining agents:
Cellulose water retaining agent
At present, the most widely used in the market is hydroxypropyl methylcellulose, followed by methyl cellulose and carboxymethyl cellulose. The overall performance of hydroxypropyl methylcellulose is better than that of methylcellulose. And the water retention of the two is much higher than that of carboxymethylcellulose. But the thickening effect and bonding effect are worse than those of carboxymethylcellulose.
In gypsum dry-mixed building materials, the dosage of hydroxypropyl and methylcellulose is generally 0.1% to 0.3%. The amount of carboxymethyl cellulose is 0.5% to 1.0%, and a large number of application examples prove that the combined use of the two has a better effect.
Starch water retaining agent
Starch water retaining agent is mainly used for gypsum putty and surface layer plaster. It can replace part or all of the cellulose water retaining agent. Adding starch-based water-retaining agent to gypsum dry powder building materials can improve the workability, workability, and consistency of slurry.
Commonly used starch-based water-retaining agents include tapioca starch, pregelatinized starch, carboxymethyl starch, and carboxypropyl starch. The amount of starch water retaining agent is generally 0.3% to 1%. If the dosage is too large, the gypsum products will be mildewed in a humid environment, which will directly affect the quality of the project.
Glue water retaining agent
Some instant adhesives can also play a better water retention role. Such as 17-88, 24-88 polyvinyl alcohol powder, Tianqing gum and guar gum, etc. They are used in gypsum dry-mix building materials such as bonding gypsum, gypsum putty, and gypsum insulation compound. In the case of a certain amount of addition, the amount of cellulose water-retaining agent can be reduced. Especially in fast-bonding gypsum, it can completely replace the cellulose ether water-retaining agent in some cases.
Inorganic water retention material
Composite with other water-retaining materials and used in gypsum dry-mixed building materials can reduce the amount of other water-retaining materials. Therefore, the cost of the product is reduced, and it also plays a certain role in improving the workability and workability of the gypsum slurry. Commonly used inorganic water-retaining materials include bentonite, kaolin, diatomaceous earth, zeolite powder, perlite powder, attapulgite clay, etc.
In future articles, we will continue to discuss “What admixtures are used for gypsum mortar?”
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1.What admixtures are used for gypsum mortar?
2.What admixtures are used for gypsum mortar?(3)
3.What admixtures are used for gypsum mortar?(4)