HPMC used in Wall Putty/Skim Coat

HPMC, or Hydroxypropyl Methyl Cellulose, serves various purposes based on its grade. In China, it's predominantly used in construction. Specifically, in the production of wall putty or skim coat, a substantial amount of skim coat powder, including HPMC and other powdery materials, is blended thoroughly and then dissolved by adding water. This method prevents agglomeration due to the immediate dissolution of HPMC particles in water.

The gel temperature of HPMC depends on its methoxy content;lower methoxy content leads to a higher gel temperature. Cold water instant-soluble HPMC, treated with glyoxal, quickly disperses in cold water, exhibiting increased viscosity but not complete dissolution. On the other hand, thermosoluble HPMC, untreated with glyoxal, disperses fast but has slower viscosity with smaller amounts. HPMC can be categorized into instant and heat-soluble types. Instant products quickly disperse in cold water and gradually increase viscosity, forming a transparent viscous colloid. Heat-soluble types, suitable for skim coat and mortar, exhibit agglomeration in liquid glue and coating.

The production of HPMC involves a solvent method using toluene or isopropyl alcohol. The application of skim coat powder requires lower viscosity, around 10,000, with a focus on water protection. Mortar applications demand higher viscosity, around 15,000, while glue applications necessitate instant products with high viscosity. The actual amount of HPMC used varies based on climate, environmental temperature, local gray calcium quality, skim coat formula, and customer quality requirements.

HPMC, with a viscosity of 100,000 in skim coat powder, plays a crucial role in water retention and thickening. However, in practical applications, a viscosity of 70,000 to 80,000 is acceptable. The main function of HPMC in skim coat includes thickening, water retention, and aiding construction. It does not participate in chemical reactions but contributes to preventing bubble formation by ensuring proper drying.

The relationship between wall putty/skim coat powder and main ash calcium quality is significant, while the influence of HPMC is limited. HPMC's role in water retention can affect powder drooping, and its interaction with water during skim coat application involves a chemical reaction, forming a new substance (calcium carbonate). However, HPMC itself does not participate in these reactions.

Various wall putty powder formulas cater to different needs, such as ordinary inner wall putty, high hardness inner wall putty, water-resistant inner wall putty, high hardness exterior wall putty, washable and mildew-proof inner wall putty, and elastic washable exterior wall anti-crack putty, among others. Each formula specifies the percentage of Redispersible Polymer Powder (RDP), double fly powder, gray calcium powder, white cement, and HPMC, tailored for specific applications like mortar, glue, or coating.