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#Self-leveling cement/mortar,#HPMC,#HEMC

Self-leveling cement/mortar, a type of flooring material that levels itself through its fluidity, is widely used in modern building flooring projects due to its high construction efficiency and excellent surface smoothness. However, achieving superior "self-leveling" results relies on a series of precisely designed chemical additives. Among them, hydroxyethyl methyl cellulose ether (HEMC) plays an indispensable key role and is hailed as a "multi-functional modifier" in self-leveling cement systems.

1. What is HEMC?

HEMC is a non-ionic cellulose ether, produced from natural cellulose through an etherification reaction. It is a white or slightly yellow powder that dissolves in water to form a clear, transparent, viscous solution. In the building materials industry, HEMC is widely used due to its excellent water retention, thickening, lubrication, and retarding properties.

1. The Core Role and Mechanism of HEMC in Self-Leveling Cement

In the complex formulation of self-leveling cement, FWD HEMC ME 400 is the most important additive. It is a specially formulated cellulose ether for self-leveling cement, with a Brookfield viscosity of 320-480 mPas. Its contributions are multifaceted, and its mechanism of action is as follows:

1. Excellent Water Retention – The “Guardian” Against Cracking

• Function: FWD HEMC ME 400forms a water film on the surface of mortar particles and locks in free water through hydrogen bonding, greatly reducing the rapid loss of water to the porous substrate.
• Mechanism: This water retention provides the necessary moisture for the continuous hydration of cement, especially in thin-layer construction and high-temperature, dry environments. Insufficient water retention prevents the cement from fully hydrating, leading to insufficient strength development and plastic shrinkage cracking.
• Importance: The excellent water retention provided by FWD HEMC ME 400is a prerequisite for obtaining high-strength, crack-free self-leveling floors.

2. Moderate Thickening and Rheological Properties – The “Master of Balance” Between Flow and Stability

• Function: FWD HEMC ME 400significantly controls the viscosity of self-leveling mortar, maintaining its high fluidity. Compared to other thickeners (such as HPMC), it has less negative impact on flowability and better meets the low shear viscosity requirements of self-leveling materials.
• Mechanism: FWDHEMC ME400 molecular chains extend in water, forming a three-dimensional network structure, giving the slurry good structural viscosity (low viscosity under high shear and high viscosity at rest).
• During Application (High Shear): Under pumping and scraping action, the viscosity temporarily decreases, making the material easy to flow and spread.
• After Settling (Low Shear): The viscosity recovers rapidly, preventing aggregates (such as silica sand) from settling and slurry stratification, ensuring the uniformity and stability of the material system and avoiding “bleeding”. • Importance: It ensures that the self-leveling material possesses both good flowability and self-healing properties, while maintaining volume stability after application.

3. Good Lubricity and Workability – Enhancing the Application Experience

• Function: FWD HEMC ME 400molecules form a lubricating layer on the surface of cement and aggregate particles, reducing friction between particles.
• Mechanism: This lubrication makes the slurry flow and spread more easily under its own weight, resulting in a smoother and more even surface. It also improves pumpability, making application smoother.

4. Retarding Effect – A “Metronome” for Controlling Application Time

• Function: FWD HEMC ME 400slightly slows down the hydration process of cement, extending the workable time of the slurry.
• Mechanism: FWD HEMC ME 400molecules adsorb onto the surface of cement particles, temporarily hindering the contact between water and cement minerals, thereby slowing down the hydration reaction.
• Importance: This is crucial for large-area construction, ensuring the material maintains good fluidity within the specified open time (usually 15-20 minutes), preventing construction joint marks due to premature setting.

III. How to Choose the Right HEMC in a Self-Leveling Compound Formulation?

The performance of HEMC varies significantly depending on its viscosity, degree of etherification, and dosage. Correct selection is key to a successful formulation.

• Viscosity Selection:
• Base Layer/Top Layer Self-Leveling: Base layer self-leveling typically uses lower viscosity HEMC (e.g., 300-500 mPa·s). Base layer self-leveling requires stronger water retention and anti-settling capabilities to handle thicker construction layers (typically 3-5 mm or more) and potentially rougher substrates.
• Top Layer Self-Leveling: Top layer self-leveling typically selects products with a viscosity below 400 mPa·s (testing conditions are generally a 2% aqueous solution at 20°C). Common commercial viscosity grades, such as 300-400 mPa·s, or even lower (around 100 mPa·s), are widely used.
• Dosage:
• The dosage of FWD HEMC ME 400 is typically 0.1%-0.4% of the total dry-mix mortar volume. Too low a dosage results in insufficient water retention and thickening; too high a dosage severely delays setting, reduces strength, and may lead to excessive viscosity, affecting leveling. Optimal dosage needs to be determined through extensive experimentation.
• Synergy with other additives:
• HEMC needs to work synergistically with components such as polycarboxylate superplasticizers, setting accelerators, defoamers, and redispersible latex powders. In particular, compatibility with superplasticizers is crucial; it is necessary to ensure that HEMC provides sufficient water retention and stability while the superplasticizer provides high fluidity.

1. Comparison of HEMC with Other Cellulose Ethers (such as HPMC)

In the self-leveling field, HPMC (hydroxypropyl methylcellulose ether) is also commonly used, but HEMC is generally considered a superior choice for the following reasons:

• **Anti-retardation:** HEMC typically has a smaller retarding effect on cement than HPMC, which is more advantageous for self-leveling systems requiring precise control of setting time.
• **Solubility and Viscosity Stability:** HEMC has better solubility in cold water, and its solution viscosity is more stable to temperature and pH.
• **Bubble Sensitivity:** HEMC introduces relatively fewer bubbles, which is more beneficial for the final strength and surface density of the slurry.

1. Common Problems and Solutions

• Problem 1: Poor fluidity, uneven flow.
• Possible Causes: HEMC viscosity is too high or the dosage is too high; poor compatibility with water-reducing agents.
• Solutions: Reduce the viscosity grade or dosage of HEMC; adjust the type or dosage of water-reducing agent.
• Problem 2: Surface bubbles or bleeding. • Possible causes: Insufficient HEMC viscosity or dosage leads to inadequate system stability; inappropriate defoamer selection.
• Solutions: Appropriately increase HEMC viscosity or dosage; optimize the defoamer system.
• Problem 3: Excessively long setting time and slow strength development.
• Possible causes: Excessively high HEMC dosage results in an overly strong retarding effect.
• Solutions: Reduce HEMC dosage; appropriately increase the amount of accelerator.

1. Conclusion

Although FWD HEMC ME 400 constitutes a small proportion in self-leveling cement formulations, its role is comprehensive and decisive. Through excellent water retention, moderate thickening, and stable rheological properties, it ensures the stable performance of self-leveling materials throughout the entire process from mixing and application to hardening. A successful self-leveling formulation is inevitably based on a deep understanding of the characteristics of key additives such as HEMC and precise compounding. It can be said that without HEMC, it is difficult to achieve a high-performance, highly stable modern self-leveling cement system.

For more details, please visit www.fwdnewtech.com or contact us at info@fwdnewtech.com.