How MHEC improves the water retention of dry-mixed mortar

In the field of building materials, dry-mixed mortar has been widely used due to its convenience and stability. However, the water retention of dry-mixed mortar is a key factor affecting construction performance and final quality. Methyl Hydroxyethyl Cellulose (MHEC), as an important cellulose ether, is widely used in dry-mixed mortar to improve its water retention.

1. Mechanism of action of MHEC in mortar

MHEC is a water-soluble polymer that mainly improves the water retention of dry-mixed mortar in the following ways:

Film-forming effect: MHEC forms a continuous hydration film inside the mortar, reducing water evaporation and improving water retention capacity.

Thickening effect: After MHEC is dissolved, it can significantly increase the viscosity of the mortar and slow down the penetration and loss of water, which is especially important in high temperature and low humidity environments.

Steric retardation effect: MHEC molecules can wrap water and make it evenly distributed in the mortar system, preventing water from seeping out too quickly and improving water utilization.

Hydration regulation: MHEC can slow down the hydration rate of cement, allowing cement to retain sufficient water for a longer period of time, thereby promoting the full progress of the hydration reaction and improving the early strength and adhesion of the mortar.

2. Specific factors affecting MHEC's improvement of water retention

The effect of MHEC on improving the water retention of dry-mixed mortar is affected by many factors, including molecular structure, degree of substitution, amount of addition, and mortar ratio.

(1) Molecular structure of MHEC

MHEC is composed of cellulose modified with methyl (–CH₃) and hydroxyethyl (–CH₂CH₂OH) substituents. The methyl group increases its hydrophobicity, while the hydroxyethyl group enhances its hydrophilicity and solubility. Appropriate degree of substitution can optimize the water solubility and balanced water absorption capacity of MHEC and improve its water retention performance.

(2) Degree of substitution (DS and MS)

DS (Degree of Substitution): refers to the number of substituted hydroxyl groups in the MHEC structure, which affects its solubility and thickening ability.

MS (Molar Substitution): refers to the average value of hydroxyethyl substituents in each glucose unit, which affects its water absorption and water retention capacity.

Generally, moderate DS and higher MS values can provide better water retention effects.

(3) Effect of addition amount

The amount of MHEC added is crucial to the water retention of dry-mixed mortar. An appropriate amount of MHEC can significantly improve water retention, but excessive addition may lead to excessive mortar viscosity and reduced construction performance. Therefore, the amount of MHEC needs to be optimized according to different application scenarios, and the general recommended range is 0.1%~0.5% (mass fraction).

(4) Effect of mortar formula

Cement type: Different cements have different hydration rates and water requirements, which affect the water retention of MHEC.

Sand particle grading: Fine sand is more helpful in improving the water retention of mortar than coarse sand.

Synergistic effect of admixtures: Used in combination with other additives (such as starch ether, water reducer, etc.), the water retention and construction performance of mortar can be optimized.

3. Application of MHEC in different dry-mix mortar systems

(1) Tile adhesive

MHEC can effectively prevent the substrate from absorbing water too quickly, increase the open time and construction fluidity of the adhesive, and enhance the bonding strength.

(2) Plaster mortar

MHEC can improve the workability, reduce water seepage, increase the water retention rate, and enable the mortar to still have good working performance in a high temperature environment.

(3) Self-leveling mortar

MHEC can control the evaporation rate of water in the self-leveling mortar, prevent cracks, and improve fluidity and uniformity.

MHEC improves the water retention of dry-mix mortar through film-forming, thickening, steric retardation and hydration regulation. Its performance is affected by factors such as molecular structure, degree of substitution, addition amount and mortar formula. In practical applications, by optimizing the MHEC ratio, the workability and final quality of dry-mix mortar can be effectively improved to meet different engineering needs.