HPMC (Hydroxypropyl methylcellulose) is generally used in putty powder with a viscosity of 100,000 mPa.s(NDJ), while mortar requires a relatively high viscosity and should be selected with a viscosity of 150,000mPa.s to achieve the desired effect. The most important role of HPMC is water retention and thickening secondly. Therefore, in putty powder, it is okay to have a lower viscosity as long as water retention is achieved. Generally speaking, the greater the viscosity, the better the water retention, but when the viscosity exceeds 100,000mPa.s, the viscosity has little effect on the water retention.
SLEOCHEM industrial-grade HPMC is divided into 4 grades according to viscosity.
Low viscosity: 400mPa.s, mainly used in self-leveling compounds. HPMC has low viscosity and good fluidity. After adding, it will control the water retention of the surface, the bleeding is not obvious, the shrinkage is small, the cracking is reduced, it can also resist precipitation, and enhance the fluidity and pumpability.
Low to medium viscosity: 20,000 – 50,000 mPa.s, typically used in gypsum products, grouts, joint fillers. Relatively low viscosity, good water retention, good workability, less water addition.
Medium viscosity: 750,000 – 100,000 mPa.s, mainly used for interior and exterior wall putty. Moderate viscosity, great water retention, and sag resistance.
High Viscosity: 150,000 – 200,000mPa.s, mainly used for polystyrene particle thermal insulation mortar, vitrified microbead thermal insulation mortar, tile adhesive, etc.
High viscosity with perfect water retention, excellent sag resistance, improved workability.
Generally speaking, the higher the viscosity of HPMC, the better the water retention. Therefore, many customers will choose to use the medium viscosity (75,000 – 100,000 mPa.s) instead of low viscosity cellulose (20,000-50,000mPa.s), to reduce the added amount and cost.