• • Blog
• March 27th 2026

The Thickening Effect of Hydroxypropyl Methylcellulose

Hydroxypropyl methylcellulose (HPMC) provides excellent consistency to wet mortars. It improves bonding between the mortar and substrate and enhances sag resistance. Therefore, it is widely used in rendering mortars, external thermal insulation systems, and tile adhesives. Its thickening effect also improves homogeneity and prevents stratification, segregation, and bleeding. HPMC is suitable for fiber-reinforced, underwater, and self-compacting concrete.

The consistency of cement-based materials depends on the viscosity of the HPMC solution. “Viscosity” is the standard measure, typically assessed using instruments like rotary viscometers under specific conditions—e.g., 2% concentration, 20°C, and 20 rpm.

Higher HPMC viscosity increases mortar consistency, adhesion, sag resistance, and dispersion resistance. However, excessively high viscosity can reduce flowability, making plaster stick to the trowel. For dry-mix mortars, HPMC viscosity usually ranges from 15,000 to 60,000 mPa·s. Lower-viscosity variants are preferred for self-leveling mortars and self-compacting concrete to maintain workability.

HPMC thickening also increases water demand, raising mortar yield.

Factors affecting HPMC solution viscosity include:

1. Molecular weight (degree of polymerization), concentration, temperature, shear rate, and test method.
2. Higher molecular weight leads to higher viscosity.
3. Higher concentration increases viscosity, but excessive dosage can reduce workability.
4. Viscosity decreases as temperature rises, with the effect more pronounced at higher concentrations.

HPMC solutions are pseudoplastic (shear-thinning). Higher shear rates reduce viscosity, aiding troweling while maintaining cohesion. At low concentrations and viscosities, they behave as Newtonian fluids. As concentration rises, pseudoplasticity becomes stronger.

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