• • Blog
• April 2nd 2026

What factors affect the viscosity of hydroxypropyl methylcellulose (HPMC)?

HPMC offers excellent thickening properties, enhancing adhesion between mortar and substrates while improving anti-sagging performance. It is widely used in plastering mortar, external insulation systems, and tile adhesives. It also improves the homogeneity and resistance to segregation of cementitious materials, preventing bleeding and settling, and is suitable for fiber-reinforced, underwater, and self-compacting concrete.

HPMC increases the viscosity of cement-based materials, mainly due to the viscosity of its own solution (typically measured at 2% concentration under standard conditions). Viscosity is a key parameter for evaluating cellulose ether performance.

Higher-viscosity HPMC improves adhesion, anti-sagging, and resistance to dispersion. However, if the viscosity is too high, it can reduce flowability and workability, making mortar difficult to apply. Therefore, dry-mix mortars usually use cellulose ethers with viscosities of 15,000–60,000 mPa·s. For applications requiring high flowability, such as self-leveling mortars, lower-viscosity products are preferred.

Additionally, HPMC’s thickening effect increases water demand, which can raise mortar yield.

What factors affect the viscosity of HPMC? It mainly depends on the following:

1. A higher degree of polymerization of the cellulose ether leads to a larger molecular weight, resulting in a higher viscosity of its aqueous solution.

2. Higher dosage or concentration of cellulose ether results in higher viscosity of the aqueous solution. However, careful selection of the appropriate dosage is crucial to avoid affecting the workability of mortar and concrete due to excessive dosage.

3. Like most liquids, the viscosity of hydroxypropyl methylcellulose ether solutions decreases with increasing temperature, and the higher the concentration of cellulose ether, the greater the effect of temperature.

4. Cellulose ether solutions are typically pseudoplastic, exhibiting shear-thinning properties. The higher the shear rate during testing, the lower the viscosity.

In summary, the cohesiveness of mortar decreases due to external forces, which is beneficial for mortar application, resulting in mortar with both good cohesiveness and workability. However, cellulose ether solutions at low concentrations and low viscosities exhibit Newtonian fluid characteristics. As the concentration increases, the solution gradually displays pseudoplastic fluid characteristics, and the higher the concentration, the more pronounced the pseudoplasticity.

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