Dissolution and effect of HPMC in wet mortar

Hydroxypropyl methylcellulose (HPMC) is a non-ionic cellulose ether widely used as a key additive in building materials, especially in wet mortar systems. After being dissolved in mortar, it can significantly improve the core properties of mortar such as workability, water retention, and adhesion.

1. Dissolution characteristics of HPMC in wet mortar

HPMC is usually added to mortar in powder form. Its dissolution process is synchronized with cement hydration. As a hydrophilic polymer, HPMC undergoes swelling in cold water and eventually forms a viscous and transparent colloidal solution. Dissolution behavior is regulated by the following factors:

Particle size: The finer the particle size, the faster the dissolution rate and the more uniform the dispersion.

Degree of substitution (DS/MS): The higher the degree of substitution, the better the hydrophilicity and solubility.

Temperature: Following the characteristics of "hot coagulation and cold dissolution", it needs to be dissolved at an appropriate temperature.

Stirring: Adequate stirring is conducive to particle dispersion and viscosity formation.

System pH value: The alkaline environment of the mortar affects the swelling stability.

2. Improvement of mortar performance by HPMC dissolution

Excellent water retention: The hydrated colloid formed by HPMC can effectively wrap water and significantly inhibit the rapid loss of water to the substrate or the environment. This ensures sufficient cement hydration, reduces the risk of plastic shrinkage cracking, and prolongs the open time.

Enhanced adhesion: The dissolved HPMC gives the mortar cohesion and adhesion to the substrate, effectively preventing slippage and delamination, especially for vertical surface construction (such as plastering and tiling).

Optimized rheology and construction properties: HPMC provides the required lubricity and consistency, improves the spreadability, pumpability and compactability of the mortar, and improves construction efficiency and surface quality.

Inhibit segregation and water seepage: The HPMC colloidal structure can stabilize the fine particles and cementitious materials in the suspended mortar, prevent aggregate sinking and surface water seepage, and ensure system uniformity.

Improved anti-sagging: In vertical applications, the viscosity and cohesion provided by HPMC significantly enhance the anti-sagging ability of mortar.

3. Effect of HPMC on the hardening process

HPMC mainly acts on the plastic stage of mortar and does not directly participate in the cement hydration reaction. It indirectly promotes more complete hydration by optimizing water distribution and retention, which is beneficial to the development of later strength and durability. At the same time, its water retention effect helps to reduce early plastic shrinkage cracks.

4. Application points

The amount of HPMC added needs to be strictly controlled. Excessive use may lead to:

Delayed early strength development

Prolonged setting time

Excessive viscosity and increased construction resistance

The formulation design should be optimized and adjusted according to the specific application (masonry, plastering, tile adhesive, insulation system, etc.) and the model of HPMC (viscosity, degree of substitution).

Conclusion

The dissolution of HPMC in wet mortar is the basis for its multiple functions. By improving water retention, adhesion, rheological properties and anti-sagging, HPMC is a key functional additive to ensure the construction performance, stability and final quality of wet mortar. With the development of green building materials and functional additives, the application of HPMC will become more extensive and refined.