As a material widely used in the construction industry, gypsum mortar is favored for its excellent thermal insulation, sound insulation, environmental protection and other properties. However, gypsum mortar often faces durability problems during use, such as cracking and peeling, which not only affects its aesthetics, but also affects the service life of the project. In order to improve the durability of gypsum mortar, many researchers have tried to optimize its performance by modifying the material. Among them, hydroxypropyl methylcellulose (HPMC), as a common water-soluble cellulose ether, has been widely used in gypsum mortar to improve the construction performance and durability of the mortar.

1. Basic characteristics of HPMC
HPMC is a derivative of cellulose, which has good water solubility, thickening and adhesive properties through chemical modification. Its molecular structure contains hydroxypropyl and methyl groups, allowing it to form a stable colloidal solution in water. HPMC is often used in building materials, especially adding HPMC to gypsum mortar, plastering mortar, etc. can significantly improve the performance of these materials.

2. Effect of HPMC on the construction performance of gypsum mortar
The construction performance of gypsum mortar is one of the important factors in its durability. Good construction performance can reduce unevenness during the construction process, improve construction efficiency, and ensure the compactness of the mortar layer, thereby improving its durability. As a thickener and water-retaining agent, HPMC plays an important role in gypsum mortar:

Thickening effect: HPMC can improve the viscosity of gypsum mortar, making the mortar more operable and avoiding construction difficulties caused by too thin or too dry mortar.

Water retention: HPMC has good water retention, which can effectively delay the evaporation of water in gypsum mortar, increase the opening time of mortar, and make it easier to apply and trim during the construction process. This helps reduce cracking problems caused by too rapid evaporation of water during construction, thereby improving the compactness and overall durability of the mortar layer.

3. Effect of HPMC on the durability of gypsum mortar
Durability is one of the important indicators of gypsum mortar, which is directly related to its service life in actual projects. The durability of gypsum mortar is mainly affected by many factors such as moisture, changes in temperature and humidity, and external forces. The addition of HPMC improves the durability of gypsum mortar in the following ways:

3.1 Enhance crack resistance
In gypsum mortar, cracks are one of the important factors affecting the durability. The rapid evaporation of water in the mortar or the dry-wet cycle will cause micro-cracks on the surface and interior of the mortar. The water retention effect of HPMC can effectively slow down the evaporation of water and prevent surface dryness, thus reducing the occurrence of cracks. At the same time, the thickening effect of HPMC can also enhance the adhesion of mortar, improve the overall stability of the mortar layer, and reduce the incidence of cracks.

3.2 Improve penetration resistance
Gypsum mortar is often exposed to humid environments during actual use. If its water absorption is too strong, the moisture inside the mortar will gradually increase, resulting in swelling, peeling and other phenomena. The addition of HPMC can improve the permeability resistance of the mortar and reduce the erosion of the internal structure of the mortar by water. The enhanced water retention enables the mortar to better maintain its structural stability and avoid performance degradation caused by moisture intrusion.

3.3 Improve freeze-thaw resistance
Gypsum mortar is often used in exterior walls or other areas that are greatly affected by weather changes, which requires the mortar to have a certain resistance to freezing and thawing. In cold regions, the repeated effects of freezing and thawing can easily cause mortar to crack. HPMC can improve the structure of mortar and increase its density, thereby enhancing its freeze-thaw resistance. By reducing moisture accumulation, HPMC reduces the damage caused by moisture expansion during freeze-thaw cycles.

3.4 Improve anti-aging performance
Over time, the strength and durability of gypsum mortar will gradually decrease. The addition of HPMC can delay the aging process by improving the microstructure of the mortar. HPMC molecules can form a protective film to reduce direct damage to the mortar surface from external environments (such as ultraviolet rays, temperature fluctuations, etc.), thereby improving its anti-aging ability.

4. HPMC usage and performance optimization
Although HPMC plays a significant role in improving the durability of gypsum mortar, its usage also needs to be moderate. Excessive addition of HPMC may cause the mortar to be too viscous, affecting construction performance, and may even have adverse effects during long-term use. Therefore, in practical applications, it is usually necessary to optimize the usage of HPMC according to the specific mortar formula and construction requirements. Generally speaking, it is ideal to control the usage of HPMC between 0.2% and 1%.

As a common modifying additive, HPMC has a positive impact on the durability of gypsum mortar. It can not only improve the construction performance of mortar, extend the opening time and improve the construction quality, but also enhance the crack resistance, permeability resistance, freeze-thaw resistance and aging resistance of mortar, thereby significantly increasing the service life of gypsum mortar. In practical applications, by reasonably controlling the amount of HPMC added, the comprehensive performance of gypsum mortar can be effectively optimized and more durable and stable building materials can be provided for the construction industry.