HPMC (Hydroxypropyl Methylcellulose) is a polymer material widely used in the construction field, especially in gypsum and cement-based dry-mixed mortar. As a modified cellulose ether, HPMC has unique physical and chemical properties, which makes it play an important role in building materials.

1. Basic properties of HPMC
HPMC is a water-soluble, colorless, odorless powdered compound with good water solubility, rheology, gelling and film-forming properties. The molecular structure of HPMC contains hydroxypropyl and methyl substituents, which makes it have good hydrophilicity and stability, and can produce good dispersibility and thickening effects in materials such as cement and gypsum. By adjusting its molecular weight, the degree of substitution of hydroxypropyl and methyl, the rheology and other functions of HPMC can be adjusted to adapt to different application requirements.

2. Application of HPMC in gypsum-based dry-mixed mortar
Gypsum-based dry-mixed mortar is a building material with gypsum as the main component, which is widely used in wall plastering, decoration and repair projects. The production process of gypsum-based mortar generally adopts a dry mixing process, that is, gypsum, fillers, expansion agents, additives and other powder raw materials are mixed and used directly. As an important additive, HPMC plays the following roles in gypsum-based mortar:

(1) Improving the operability of mortar
Gypsum-based mortar often needs to have good operability during construction, such as good adhesion, moderate viscosity and easy smoothing. HPMC improves the rheological properties of mortar, making the mortar have a suitable consistency, avoiding construction difficulties caused by being too dry or too wet. It can effectively improve the bonding performance of mortar and prolong the open time, thereby improving the operating efficiency of construction personnel.

(2) Improving the water retention of mortar
Gypsum material has strong water absorption, which can easily cause the mortar to dry too quickly, thus affecting the workability and final hardening quality of the mortar. HPMC has good water retention and can effectively reduce water evaporation, thereby delaying the drying process of the mortar, ensuring that the gypsum-based mortar has a longer open time and better finishability during construction. This is of great significance for improving construction quality.

(3) Improving the strength and durability of mortar
HPMC can not only improve the workability of mortar, but also improve its strength and durability. By adjusting the dosage and type of HPMC, the mechanical properties of mortar can be optimized, and the compressive strength and flexural strength of mortar can be increased. At the same time, HPMC can enhance the crack resistance of mortar and reduce cracks caused by drying shrinkage or temperature changes, thereby improving the durability of mortar.

3. Application of HPMC in cement-based dry-mixed mortar
Cement-based dry-mixed mortar is widely used in construction such as walls, floors, exterior wall insulation, plastering, etc., and has a high market demand. In cement-based mortar, the role of HPMC is mainly reflected in the following aspects:

(1) Improving the fluidity and workability of mortar
In cement-based mortar, HPMC, as a thickener, can effectively improve the fluidity of mortar, making it easier to construct and operate. During the construction process, the fluidity of mortar directly affects the construction efficiency and quality. By adding an appropriate amount of HPMC to cement-based mortar, its consistency can be improved, so that the mortar can show good operability in different construction environments.

(2) Improve water retention and reduce water seepage
During the hardening process of cement-based mortar, if the water evaporates too quickly, it is easy to cause water seepage, which in turn affects the strength and surface quality of the mortar. HPMC can improve the water retention of cement-based mortar, avoid excessive volatilization of water, ensure the uniformity and stability of the mortar, thereby improving the construction quality and strength after hardening.

(3) Enhance crack resistance
During the hardening process, cement-based mortar often shrinks, resulting in cracks on the surface or inside of the mortar. HPMC effectively reduces the crack formation of cement-based mortar by improving the rheology of the mortar, increasing its plasticity and adhesion. This anti-cracking effect not only improves the aesthetics of the mortar, but also enhances its durability in long-term use.

(4) Delay hardening time
HPMC can adjust the hydration rate of cement-based mortar, thereby delaying the hardening time. This is particularly important when working at high temperatures or over a large area, as it can provide more operating time for construction workers and reduce construction quality problems caused by too fast hardening.

4. Advantages of HPMC in gypsum and cement-based dry-mixed mortar
(1) Good rheological control
HPMC can significantly improve the rheological properties of mortar, including thickening, viscosity enhancement, and water retention, thereby improving the construction performance of mortar. By precisely adjusting the amount of HPMC, the construction properties of mortar can be optimized to meet the needs of different construction environments.

(2) Excellent adhesion and water retention
Whether in gypsum-based or cement-based mortar, HPMC can effectively enhance the adhesion and water retention of mortar, reduce the cracking of mortar, and ensure operability and hardening quality during construction.

(3) Environmental protection and safety
HPMC is a non-toxic, odorless, environmentally friendly chemical that meets the requirements of green and environmental protection of modern building materials. Therefore, the use of HPMC can not only improve the performance of mortar, but also ensure the safety of the construction environment.

HPMC plays an important role in the application of gypsum and cement-based dry-mix mortar. It improves the workability, strength and durability of the mortar by improving the rheology, adhesion, water retention and other properties of the mortar. With the increasing demand for high-performance building materials in the construction industry, the application prospects of HPMC are very broad, especially in the production and construction of dry-mix mortar, HPMC will continue to play an indispensable role.