What are the key roles of cellulose ether in self leveling mortar? ​

cellulose etherIt is an essential core functional additive in self leveling mortar. It is not an aggregate or cementitious material, but can determine whether the mortar can achieve "self leveling" and ensure engineering quality from multiple dimensions such as workability, mechanical properties, and durability. Its key role is mainly reflected in the following six aspects.

1、 Water retention function, preventing bleeding and segregation

Self leveling mortar is composed of multiple components such as cement, fine aggregates, fillers, and additives. The water cement ratio directly affects its flowability and strength, while the strong water retention of cellulose ether is the basic guarantee.

The molecular structure of cellulose ether contains a large number of hydroxyl groups, which can form hydrogen bonds with water molecules, firmly locking in the mixed water, preventing water from quickly penetrating into the base layer, migrating inside the mortar, or causing segregation phenomena such as aggregate sinking and slurry layering.

This function ensures that all components of the mortar are evenly dispersed during the construction process, and the flowability does not significantly decrease over time. It also provides sufficient and stable moisture for the cement hydration process, avoiding incomplete hydration caused by rapid water loss, such as sanding, cracking, and insufficient strength. It is especially suitable for base floors with high water absorption rates.

2、 Thickening and rheological adjustment to achieve ideal self leveling

The core characteristic of self leveling mortar is that it does not require vibration and can be leveled and leveled by its own gravity, which is inseparable from the thickening and rheological modification of cellulose ether.

cellulose etherAfter dissolving in water, it will significantly increase the viscosity of the slurry, construct a stable internal colloidal structure, and give the mortar a suitable yield value. This structure gives the mortar thixotropy: it has a high viscosity at rest, which can support the aggregate and prevent settlement; When subjected to the shear force of the construction scraper and its own gravity, the viscosity rapidly decreases, exhibiting excellent flowability; After losing external force, the viscosity quickly recovers, avoiding excessive flow and uneven edge flow. At the same time, the flowability of the mortar is effectively controlled, allowing it to spread quickly and accurately control the leveling range, forming a flat and uniform base surface.

3、 Delay condensation and extend the construction window period

The hydration and setting speed of cement is fast. Without a retarding component, the mortar will lose its fluidity in a short period of time and cannot complete large-scale construction. Cellulose ether has a slight retarding effect. It wraps around the surface of cement particles, delaying the contact between cement and water and slowing down the generation rate of hydration products.

This function will not excessively reduce the early strength of the mortar, but will reasonably extend the initial and final setting time, reserve sufficient operating time for construction personnel, ensure the continuity of large-scale ground construction, avoid problems such as obvious construction joints, junctions, and uneven surfaces, and improve construction efficiency and overall aesthetics.

4、 Introducing microbubbles to optimize the internal structure of mortar

High quality cellulose ether can uniformly introduce a large number of small, closed, and stable bubbles during the mortar mixing process. These bubbles are not harmful large bubbles, but rather the "structural modifiers" of the mortar.

On the one hand, microbubbles can play a ball rolling effect, further enhancing the fluidity of mortar and reducing construction resistance; On the other hand, uniformly distributed microbubbles can alleviate the shrinkage stress generated during the cement hydration process, reduce the occurrence of dry shrinkage and plastic shrinkage cracks, while reducing the density of mortar, improving its toughness, and avoiding cracking and hollowing of the ground due to stress concentration.

5、 Improve bonding strength and enhance adhesion to the substrate

Self leveling mortar needs to be closely combined with the base ground to prevent later cracking and hollowing, and cellulose ether plays a key role in bonding and assisting.

It enhances the viscosity of the mortar, allowing the slurry to better infiltrate the surface of the base layer, fill the small pores of the base layer, increase the contact area and mechanical biting force between the mortar and the base layer; At the same time, the stable colloidal structure forms a strong interface bond between the mortar and the base layer, effectively improving the bonding strength of the interface, preventing delamination and hollowing, and ensuring the integrity and service life of the ground.

6、 Suppress stratification and settlement to ensure uniform performance

The density difference between fine aggregates and fillers in self leveling mortar is significant. Under high fluidity conditions, there is a tendency for heavy aggregates to sink and light components to float, resulting in uneven strength and compactness of the upper and lower layers of mortar, and sanding and uneven strength on the ground.

cellulose etherThe formed colloidal network can suspend and support each component, limit the free settling of solid particles, and ensure that the components of the mortar are uniformly distributed throughout the entire construction and setting process. After forming in this way, the overall density, strength, and wear resistance of the ground are highly consistent, and there will be no local weak areas, improving the durability of the ground.

Addendum: Key points for selecting different types of cellulose ethers

Hydroxypropyl methyl cellulose ether (HPMC) is commonly used in self leveling mortar, and hydroxyethyl methyl cellulose ether (HEMC) may be used in some scenarios. When selecting, the key is to consider the viscosity index:

Low viscosity cellulose ether: focusing on improving fluidity, suitable for ultra-thin layer self leveling with high fluidity requirements;

Medium to high viscosity cellulose ether: focuses on water retention, thickening, and anti settling, suitable for self leveling mortar with thick layers and high aggregate content.