Cellulose ether improves mortar water retention.
Viscosity is an important parameter for the properties of cellulose ether.
Generally speaking, the higher the viscosity, the better the water retention effect of gypsum mortar. However, the higher the viscosity, the higher the molecular weight of the cellulose ether, and its solubility will decrease accordingly. This has a negative impact on the strength and workability of the mortar.
The higher the viscosity, the more obvious the thickening effect on the mortar, but the relationship is not directly proportional.
The higher the viscosity, the stickier the wet mortar will be. During construction, it is characterized by sticking to the scraper and high adhesion to the substrate. But it does not help much to increase the structural strength of the wet mortar itself. In addition, during construction, the anti-sag performance of wet mortar is not obvious. On the contrary, some modified methylcellulose ethers with medium and low viscosity have excellent performance in improving the structural strength of wet mortar.
The reasons and functions of adding water-retaining agents to gypsum buildings.
Most building wall materials are porous structures, and they all have strong water absorption. The gypsum building materials used in wall construction are mixed with water and then put on the wall. Moisture is easily absorbed by the wall, causing the gypsum to lack the moisture necessary for hydration. This causes difficulty in plastering construction and reduces bonding strength. As a result, quality problems such as cracks, hollows, and peeling may occur.
Improving the water retention of gypsum building materials can improve the construction quality and improve the bonding force with the wall. Therefore, water-retaining agent has become one of the important admixtures for gypsum building materials.
When using plastering gypsum, bonding gypsum, caulking gypsum, gypsum putty and other building powder materials. In order to facilitate construction, gypsum retarder is added during production to extend the construction time of gypsum slurry. Since the gypsum is mixed with a retardant, the hydration process of semi-hydrated gypsum is inhibited.
This type of gypsum slurry needs to be kept on the wall for 1 to 2 hours before it sets. Most walls have water-absorbing properties, especially new lightweight wall materials such as brick walls, aerated concrete walls, and porous insulation boards. Therefore, the gypsum slurry needs to be treated with water retention. Prevent some of the moisture in the slurry from transferring to the wall. As a result, the gypsum slurry lacks water when it hardens, and the hydration is incomplete. Causes separation and crusting at the joint between gypsum and wall.
Commonly used cellulose ether water retaining agents.
Adding a water-retaining agent is to maintain the moisture contained in the gypsum slurry and ensure the hydration reaction of the gypsum slurry at the interface, thereby ensuring the bonding strength. Commonly used water-retaining agents are cellulose ethers, such as methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), hydroxyethylmethylcellulose (HEMC), etc. In addition, polyvinyl alcohol, sodium alginate, modified starch, diatomaceous earth, rare earth powder, etc. can also be used to improve water retention performance.
No matter what kind of water-retaining agent, it can delay the hydration speed of gypsum to varying degrees. When the retarder dosage remains unchanged, the water-retaining agent can generally retard the setting for 15 to 30 minutes. Therefore, the amount of retarder can be appropriately reduced.
Landcel is a manufacturer that produces and sells cellulose ether products. Cellulose ether products of different types and viscosities can be customized according to needs. The main products are HPMC, HEMC, HEC, EHEC, CMC, RDP.