There are limitations in the improvement of the performance of gypsum slurry by a single admixture. In order to achieve satisfactory performance of gypsum mortar and meet different application requirements, chemical admixtures, admixtures, fillers and various materials are required to be compounded and complemented scientifically and rationally.

1 coagulant
Coagulation modifiers are mainly divided into retarders and accelerators. In the gypsum dry-mixed mortar, the products formulated with plaster of paris all use a setting retarder, and the products formulated with anhydrite or directly using dihydrate gypsum require a setting accelerator.

2 retarder
Adding retarder to gypsum dry-mixed building materials inhibits the hydration process of hemihydrate gypsum and prolongs the setting time. Conditional factors for the hydration of plaster of paris are various, including the phase composition of the plaster of paris, the temperature of the plaster of paris material when formulating the product, the fineness of the particles, the setting time and the pH value of the finished product. Each factor has a certain influence on the retarding effect, so the dosage of retarder under different circumstances is quite different. At present, the best special retarder for gypsum in China is a metamorphic protein (high protein) retarder, which has the advantages of low cost, long retardation time, small strength loss, good product construction and long open time. In the preparation of bottom-type stucco gypsum, the dosage is generally 0.06% to 0.15%.

3 coagulant
Accelerating the stirring time of the slurry and prolonging the stirring speed of the slurry are all methods of physical coagulation. Chemical coagulants commonly used in anhydrite powder building materials include potassium chloride, potassium silicate, sulfate and other acids. The dosage is generally 0.2% to 0.4%.

4 water retention agent
Gypsum dry-mixed building materials are inseparable from water-retaining agents. To improve the water retention rate of the gypsum product slurry is to ensure that the water can exist in the gypsum slurry for a long time, so as to obtain a good hydration and hardening effect. Improving the workability of gypsum powder building materials, reducing and preventing the segregation and bleeding of gypsum slurry, improving the sag of the slurry, extending the opening time, and solving engineering quality problems such as cracking and hollowing are all inseparable from water-retaining agents. Whether the water retention agent is ideal mainly depends on its dispersibility, instant solubility, moldability, thermal stability and thickening, among which the most important indicator is water retention.

① Cellulose water-retaining agent

At present, the most widely used in the market is hydroxypropyl methyl cellulose, followed by methyl cellulose, and then carboxymethyl cellulose. The comprehensive performance of hydroxypropyl methyl cellulose is better than that of methyl cellulose, and the water retention of the two is much higher than that of carboxymethyl cellulose, but the thickening effect and bonding effect are worse than that of carboxymethyl cellulose. In gypsum dry-mixed building materials, the dosage of hydroxypropyl and methyl cellulose is generally 0.1% to 0.3%, and the dosage of carboxymethyl cellulose is 0.5% to 1.0%. It has been proved by a large number of application examples that the combined effect of the two is better. .

②Starch water-retaining agent

Starch water-retaining agent is mainly used for gypsum putty and surface plastering gypsum, and can replace part or all of cellulose water-retaining agent. Adding starch water-retaining agent to gypsum dry powder building materials can improve the workability, workability and consistency of the slurry. Commonly used starch water-retaining agent products include tapioca starch, pregelatinized starch, carboxymethyl starch, carboxypropyl starch, etc. The dosage of starch water-retaining agent is generally 0.3% to 1%. If the dosage is too large, the gypsum product will be mildewed in a humid environment, which will directly affect the quality of the project.

③Glue type water-retaining agent

Some instant adhesives can also play a better role in water retention. For example, 17-88, 24-88 polyvinyl alcohol powder, Tianqing gum and guar gum are used in gypsum dry-mixed building materials such as gypsum, gypsum putty, and gypsum thermal insulation compound. The dosage of cellulose water-retaining agent can be reduced. Especially in the quick-bonding gypsum, in some cases, it can completely replace the cellulose ether water-retaining agent.

④Inorganic water retention material

The application of composite other water-retaining materials in gypsum dry-mixed building materials can reduce the amount of other water-retaining materials, reduce product costs, and also play a certain role in improving the workability and workability of gypsum slurry. Commonly used inorganic water-retaining materials are bentonite, kaolin, diatomite, zeolite powder, perlite powder, attapulgite clay, etc.

5 Adhesives
The application of adhesives in gypsum dry-mixed building materials is second only to water-retaining agents and retarders. Gypsum self-leveling mortar, bonding gypsum, caulking gypsum, and thermal insulation gypsum glue are all inseparable from adhesives.

Dispersible polymer powder:

Redispersible latex powder is widely used in gypsum self-leveling mortar, gypsum thermal insulation compound, gypsum caulking putty, etc. Especially in gypsum self-leveling mortar, it can make the slurry sticky and fluid, and it also plays a great role in reducing delamination, avoiding bleeding, and improving crack resistance. The dosage is generally 1.2% to 2.5%.

Instant polyvinyl alcohol:

At present, the most widely used instant polyvinyl alcohol on the market is 24-88 and 17-88 products, which are commonly used in bonding gypsum, gypsum putty, gypsum composite thermal insulation compound, plastering gypsum and other products. 0.4% to 1.2%.

Guar gum, Tian Qing gum, carboxymethyl cellulose, starch ether, etc. are all adhesives with different bonding functions in gypsum dry-mixed building materials.

6 thickener
Thickening is mainly to improve the workability and sag of gypsum slurry, which is similar to adhesives and water-retaining agents, but not completely. Some thickener products are effective in thickening, but not ideal in terms of cohesion and water retention. When preparing gypsum dry powder building materials, the main role of admixtures should be fully considered in order to better and more rationally apply admixtures. Commonly used thickener products are polyacrylamide, Tian Qing gum, guar gum, carboxymethyl cellulose, etc.

7 Air-entraining agent
Air-entraining agent, also known as foaming agent, is mainly used in gypsum dry-mixed building materials such as gypsum thermal insulation compound and plastering gypsum. Air-entraining agent (foaming agent) helps to improve workability, crack resistance, frost resistance, and reduce bleeding and segregation. The dosage is generally 0.01% to 0.02%.

8 Defoamers
Defoamers are often used in gypsum self-leveling mortar and gypsum caulking putty, which can improve the density, strength, water resistance and cohesiveness of the slurry. The dosage is generally 0.02% to 0.04%.

9 water reducer
Water reducing agent can improve the fluidity of gypsum slurry and the strength of gypsum hardened body, and is usually used for gypsum self-leveling mortar and plastering gypsum. At present, the domestic superplasticizers are arranged in terms of fluidity and strength effect: polycarboxylate retarder superplasticizer, melamine superplasticizer, tea-based superplasticizer, and lignosulfonate superplasticizer. When using water reducer in gypsum dry-mixed building materials, in addition to considering water consumption and strength, attention should also be paid to the loss of setting time and fluidity of gypsum building materials over time.

10 Water repellent
The biggest defect of gypsum products is the poor water resistance, and the water resistance of gypsum dry-mixed mortar is higher in areas with high air humidity. Generally, the water resistance of gypsum hardened body is improved by adding hydraulic admixture. In the case of wet or saturated water, the external addition of hydraulic admixture can make the softening coefficient of the gypsum hardened body reach more than 0.7, so as to meet the requirements of product strength. Chemical admixtures can also be used to reduce the solubility of gypsum (that is, increase the softening coefficient), reduce the adsorption of gypsum to water (that is, reduce the water absorption rate), and reduce the corrosiveness of the gypsum hardened body (that is, the water-resistant approach to water isolation). Gypsum waterproofing agents include ammonium borate, sodium methylsiliconate, silicone resin, emulsified paraffin, and silicone emulsion waterproofing agents with better effects.

11 Active Stimulators
Activation of natural and chemical anhydrite can make it sticky and strong, suitable for the production of gypsum dry-mixed building materials. The acid activator can accelerate the early hydration rate of anhydrite, shorten the setting time, and improve the early strength of gypsum hardened body. The alkaline activator has little effect on the early hydration rate of anhydrite, but can significantly improve the later strength of the gypsum hardened body, and can generate some hydraulic cementitious materials in the gypsum hardened body, effectively improving the water resistance of the gypsum hardened body. sex. The effect of the acid-base complex activator is better than that of a single acid or alkaline activator. Acid stimulators include potassium alum, sodium sulfate, potassium sulfate, etc. Alkaline activators include quicklime, cement, cement clinker, calcined dolomite, etc.

12 Thixotropic lubricant
The thixotropic lubricant is used in self-leveling gypsum or plastering gypsum, which can reduce the flow resistance of gypsum mortar, prolong the opening time, prevent the stratification and sedimentation of the slurry, so that the slurry can obtain good lubricity and workability. The body structure is uniform while increasing its surface strength