HPMC (hydroxypropyl methylcellulose), as an important chemical additive, is widely used in dry-mixed mortar. Its main function is to improve the water retention performance of the mortar. Water retention performance has an important impact on the performance of mortar and final construction effect. The application of HPMC in dry-mixed mortar can effectively improve its constructability, bonding strength, durability, etc., thereby improving construction quality and construction efficiency.

1. Basic properties and working principles of HPMC
HPMC is a non-ionic cellulose ether with good water solubility. It forms a colloidal solution after dissolving in water, which can significantly enhance the water retention capacity of the mortar. Its water retention property comes from the water-absorbing molecular structure of HPMC. Hydroxypropyl and methyl substituents give it hydrophilicity, allowing it to form a sticky substance in the presence of water molecules, thereby reducing water loss. At the same time, HPMC molecules form a network structure through hydrogen bonding, which plays a role in fixing moisture in the mortar. This unique chemical structure makes it an ideal water-retaining agent in dry-mix mortars.

2. Effect of HPMC on water retention performance of dry mixed mortar
(1) Improve the workability of mortar
The water retention effect of HPMC can effectively prolong the evaporation time of water in the mortar, making the mortar less likely to lose water in hot or dry environments, thereby maintaining good construction performance. This water-holding capacity is particularly important for outdoor construction, helping to ensure the plasticity of the mortar during laying or plastering, making it easier to apply and level. At the same time, good water retention reduces the risk of shrinkage and cracking caused by water loss and improves the stability and uniformity of construction.

(2) Enhance bonding strength
Moisture in cement-based materials is critical to the cement hydration reaction. HPMC ensures sufficient hydration of cement through its water retention effect, thus enhancing the bonding strength between cement and substrate. When the water in the mortar is lost too quickly, the cement cannot complete the hydration reaction, resulting in a decrease in bonding strength. The addition of HPMC effectively maintains the moist state in the mortar and ensures the hydration reaction, thus improving the bonding performance.

(3) Improve the crack resistance and durability of mortar
Rapid water loss often causes shrinkage cracks in the mortar, affecting the overall strength and appearance. HPMC can form a water-holding film in the mortar, effectively reducing the evaporation rate of water in the mortar, thereby reducing the probability of shrinkage and cracking. In addition, good water retention properties help improve the density of the mortar, thereby improving its anti-freeze and anti-permeability properties, making the mortar still have high durability in harsh environments such as moisture and cold.

3. The amount of HPMC added and its influencing factors
The water retention performance of HPMC is closely related to the amount added to the mortar. Generally speaking, the amount of HPMC added is between 0.1% and 0.5%. The specific amount needs to be adjusted according to the type of mortar, construction environment, etc. Adding too little HPMC may not meet the water retention needs, while adding too much may cause the mortar to be too viscous and difficult to construct. Therefore, in practical applications, the appropriate HPMC dosage needs to be determined based on the needs of the mortar and the actual effect.

In addition, the water retention effect of HPMC will also be affected by its molecular weight, degree of substitution, particle size and other factors. For example, HPMC with high molecular weight usually has better water retention properties, but the viscosity also increases accordingly, requiring a balance between workability and water retention. In addition, the dissolution rate of HPMC will also affect the water retention effect of the mortar, so it is necessary to ensure that it is fully dissolved when preparing dry-mixed mortar.

4. Application prospects and development of HPMC
As an environmentally friendly water-retaining agent, HPMC has broad application prospects. As the construction industry’s requirements for material quality and construction efficiency increase, HPMC is increasingly used in dry-mix mortar. In the future, research on HPMC will further focus on improving its water retention performance and environmental friendliness. For example, the water retention performance and use effect of HPMC can be further improved through molecular structure modification, compound additives, etc. In addition, with the increase in environmental protection requirements, HPMC production processes with low energy consumption and low pollution will also become the focus of research.

The application of HPMC in dry-mixed mortar greatly improves the water retention performance of the mortar, thereby improving the workability, bonding strength and durability of the mortar. Its unique water retention effect not only ensures the stable performance of the mortar during construction, but also effectively extends the service life of the mortar. With the development of the construction industry, the application of HPMC in dry mixed mortar will become more and more extensive.