Hydroxypropyl methylcellulose (HPMC) is a non-ionic cellulose ether widely used in building materials, especially mortar and plaster. As an additive, HPMC can significantly improve the various properties of these materials, including workability, water retention, crack resistance, etc.

1. Chemical properties and structure of HPMC

HPMC is a semi-synthetic polymer obtained by modifying the hydroxyl groups of cellulose through methylation and hydroxypropylation. Its basic structural unit is glucose, which is connected by β-1,4-glycosidic bonds. The long chain of cellulose gives it good film-forming and adhesive properties, while the introduction of methyl and hydroxypropyl groups improves its solubility and stability.

The chemical structure of HPMC gives it the following characteristics:

Water solubility: It can dissolve quickly in cold water to form a transparent viscous liquid.

Viscosity adjustment: The solution of HPMC has an adjustable viscosity, which depends on its molecular weight and concentration.

Stability: It is stable to acids and bases and can maintain its performance over a wide pH range.

2. Mechanisms of HPMC to improve the performance of mortar and plaster

(2.1). Improve water retention
Water retention refers to the ability of mortar or plaster to retain water, which is crucial to the cement hydration and hardening process. HPMC improves water retention through the following mechanisms:

Film-forming effect: HPMC forms a thin film in mortar or plaster, slowing down the evaporation rate of water.
Molecular water absorption: HPMC molecules can absorb a large amount of water, reducing water loss during construction.
High water retention helps to fully hydrate cement, thereby improving the strength and bonding properties of mortar and plaster. In addition, it also reduces the formation of cracks caused by excessive water loss.

(2.2). Improve workability
Workability refers to the operating performance of mortar and plaster during the construction process, such as fluidity and workability. The mechanisms by which HPMC improves workability include:

Improving plasticity: HPMC provides good lubricity, giving the mixture better plasticity and fluidity.
Preventing delamination and segregation: The thickening effect of HPMC helps maintain an even distribution of particles, preventing delamination or segregation in mortar or plaster.
This makes the mortar or plaster easier to work with during construction, allowing for more even application and shaping, reducing the possibility of waste and rework.

(2.3). Increased crack resistance
Mortar and plaster may crack due to volume shrinkage during hardening, and HPMC helps reduce this phenomenon:

Flexibility: The network structure formed by HPMC in the material increases the flexibility of mortar and plaster, thereby absorbing and relieving stress.
Uniform drying: Because HPMC provides good water retention, water can be released evenly, reducing volume changes during drying.
These properties reduce the possibility of crack formation and improve the durability of the material.

3. Examples of HPMC applications in mortar and plaster

(3.1). Tile adhesive
In tile adhesive, HPMC provides excellent water retention and anti-slip properties, allowing tiles to adhere firmly to the substrate and maintain good construction operability.

(3.2). Self-leveling mortar
Self-leveling mortar requires high fluidity and self-compacting properties. HPMC’s high water retention and viscosity adjustment capabilities help achieve these requirements, resulting in a smooth surface.

(3.3). Plaster
HPMC increases the adhesion and crack resistance of plaster, especially in exterior wall plastering applications, and can resist cracking and falling off caused by various environmental factors.

4. Precautions for the use of HPMC

(4.1). Usage
The amount of HPMC used in mortar and plaster is usually a small amount in terms of weight percentage, such as 0.1% to 0.5%. Too much HPMC will result in excessive viscosity and affect workability; too little will make it difficult to significantly improve performance.

(4.2). Compatibility with other additives
When using HPMC, it is necessary to consider compatibility with other chemical additives (such as water reducers, air entraining agents, etc.) to ensure that no adverse chemical reactions occur or the final performance of the material is affected.

As an important chemical additive, the application of HPMC in mortar and plaster significantly improves its water retention, workability and crack resistance. These improvements not only enhance the construction effect and material quality, but also improve the durability and reliability of the project. In specific applications, by reasonably adjusting the dosage and ratio of HPMC, the performance of mortar and plaster can be effectively optimized.