Selection Method for Difference Water Retention of HPMC in Gypsum

The dosage of HPMC(hydroxypropyl methylcellulose) in different applications is different, mainly determined by the need for water retention. Hydroxypropyl methylcellulose is suitable for various mortars.

Water retaining agents are commonly used in building powder materials such as plastering gypsum, bonding gypsum, caulking gypsum, and gypsum putty. The dosage is generally 0.1%~0.2% (accounting for the amount of gypsum). When gypsum slurry is used for walls with strong water absorption and for the preparation of bonding gypsum, caulking gypsum, surface plastering gypsum or surface thin putty, the dosage of water retaining agent needs to be larger (generally 0.2%~0.5%).

Although water retaining agents such as hydroxypropyl methylcellulose (HPMC) and methylcellulose (MC) are cold-soluble, they will form lumps when directly dissolved in water. The water retaining agent needs to be pre-mixed in gypsum powder and dispersed to prepare dry powder; after adding water and stirring, let it stand for 5 minutes and stir again for better results.

The higher the water retention of mortar, the better. This concept is incorrect. The water retention of mortar should be controlled within an appropriate range.

Reason: If the water retention is too good, it will cause mortar beach wall, bubbling and hollowing when encountering a shear wall that does not absorb water; if the water retention is too high, the mortar layer will not dry, and the plastering workers will rush the deadline and rub the hair in advance, causing the mortar to sag and crack. If the water retention is too good, it is easy to make the mortar sticky and the construction performance is poor. The plasterers rub back and forth, causing the mortar layer to hollow.

Since this type of gypsum is mixed with a retarder, which inhibits the hydration process of semi-hydrated gypsum, the gypsum slurry must be treated with water retention. Adding a water retaining agent is to maintain the moisture contained in the gypsum slurry, thereby ensuring the bonding strength.

(Such as aerated concrete, perlite insulation board, gypsum blocks, brick walls, etc.)