HPMC (hydroxypropyl methylcellulose) is a crucial component in the creation of dry mix mortars. Its significance might not be immediately apparent to those unfamiliar with it, yet it greatly influences the smoothness and uniformity of the mortar, simplifying construction processes. This article elucidates the advantages of integrating HPMC into dry mix mortars, highlighting its numerous benefits.

 

What is HPMC (Hydroxypropyl methylcellulose)?

 

HPMC (Hydroxypropyl methylcellulose), also known as hypromellose, is a type of non-ionic cellulose ether. It typically appears as a white powder or loose fibrous material, with particles sized to pass through an 80-mesh sieve. It is odorless, tasteless, and non-toxic, and does not react with heavy metals. Variations in methoxyl and hydroxypropyl content, as well as viscosity, yield different types of HPMC. HPMC is essentially methyl cellulose modified with epoxy methane (methyl oxirane), which gives it similar solubility characteristics to methyl cellulose—soluble in cold water and insoluble in hot water. Additionally, it exhibits better solubility in organic solvents than in water, with a wide range of solvents capable of dissolving it, including methanol, ethanol, dichloromethane, trichloroethane, acetone, isopropanol, and diacetone alcohol.

 

HPMC is utilized across various industries for multiple applications. It is commonly found in construction, building materials, dispersible coatings, wallpaper paste, polymerization additives, paint removers, leather products, ink, and paper-making. Its versatility allows it to serve as thickeners, adhesives, water retention agents, film-forming agents, excipients, and binders. In construction, it acts as a binder, thickener, and water-retaining agent, while in the coating industry, it functions as a film-forming agent and thickener. Moreover, it sees widespread use in oil drilling and the daily chemical industry.

 

Why is HPMC Important in Dry Mix Mortar?

 

HPMC is primarily manufactured through the alkalization and etherification of wood pulp or cotton fibers (locally sourced). As it lacks any charge, it doesn't interact with charged ions in the gelling material, ensuring stable performance. Moreover, it's more cost-effective compared to other cellulose ethers, making it a preferred choice for dry mix mortars.

 

HPMC serves as a crucial component in dry mix mortar, functioning as a water retention and thickening agent. It enhances the wet viscosity of fresh mortar, mitigating segregation. The retention of water is vital, allowing the cementitious material ample time to hydrate post-application. By incorporating a small quantity of HPMC into the dry mix mortar, a notable increase in water retention can be achieved. However, this effect diminishes as the HPMC content reaches a certain threshold. Typically, the water retention capacity of HPMC decreases with rising ambient temperatures, although some modified versions exhibit superior water retention even in high temperatures. Additionally, HPMC possesses air-entraining properties, enhancing the workability of mortar by introducing fine air bubbles.

 

In dry mix mortar, even a small addition of HPMC can notably enhance the performance of the wet mortar. It has been demonstrated as a crucial additive influencing the construction performance of mortar.

 

 

3 Benefits of Adding HPMC to Your Dry Mix Mortars

 

Water retention, thickening, and improvement of construction performance are the primary benefits of HPMC in dry mortars.

 

1. Water Retention

 

Water retention stands as a crucial quality indicator for HPMC, especially in thin-set applications like cement mortar and gypsum-based products. Enhanced water retention ensures that the mortar doesn't dry out prematurely or undergo inadequate hydration, thereby maintaining its strength and minimizing the risk of cracking.

 

2. Thickening

 

HPMC excels as a thickening agent, significantly boosting viscosity when incorporated into dry mortar. This enhancement leads to improved bond strength, fluidity, structural stability, and resistance to sagging.

 

3. Workability

 

HPMC contributes to mortar's excellent fluidity and facilitates appropriate air entrainment. This results in reduced mortar density, improved workability, and increased mortar output. Furthermore, the presence of air within the mortar enhances the thermal insulation properties of the final products.

 

Typical Applications of HPMC in Dry Mix Mortars.

 

1. Plastering Mortar

 

Incorporating HPMC into plastering mortar boosts water retention, ensuring thorough hydration of cement. This enhances bond strength, as well as tensile and shear strength, resulting in significantly improved construction outcomes and increased work efficiency.

 

2. Wall Putty

 

Within wall putty, HPMC serves key functions such as water retention, bonding, and lubrication. It safeguards against cracks and dehydration resulting from excessive water loss while bolstering putty adhesion. Moreover, it mitigates sagging during construction, ensuring a smoother construction process overall.

 

3. Gypsum Plaster

 

HPMC plays a significant role in gypsum-based products by enhancing water retention and lubrication. It also exhibits a retarding effect, preventing hollow cracking and ensuring attainable initial strength during construction, thereby extending the working time.

 

4. EIFS/ETICS Mortars

 

Within EIFS/ETICS systems, HPMC enhances bonding and strength, facilitates smoother coating of mortar, and improves overall efficiency. It also exhibits a robust anti-sag effect and increased water retention, extending the mortar's working time while minimizing shrinkage and cracking. Additionally, it enhances surface quality and bond strength.

 

5. Tile Adhesive

 

The addition of HPMC to tile adhesive enhances its water retention properties, minimizing moisture absorption by both the substrate and tiles. This ensures that moisture remains in the binder for extended periods, allowing for prolonged application time while preserving adhesiveness. Moreover, maintaining the proper viscosity of the mortar ensures consistency, enhances wetting ability, and improves adhesion.

 

6. Joint Filler/Grouts

 

In joint filler/grouts, HPMC offers excellent abrasion and shrinkage resistance, safeguarding the base material against mechanical damage and infiltration.

 

7. Self-Leveling Compounds

 

Incorporating HPMC into self-leveling compounds enhances fluidity and self-leveling properties while regulating water retention rates. This promotes rapid setting, minimizing the occurrence of cracking and shrinkage.

 

Final Remarks

 

Although the quantity of HPMC added to dry mortar is minimal, its impact on the performance of wet mortar is significant, making it a key additive influencing mortar performance during construction. HPMC primarily contributes to water retention, thickening, and enhancing the performance of dry mix mortars. By selecting the appropriate grades and proportions of HPMC, the performance of dry mortar can be notably enhanced.

 

While HPMC is considered cutting-edge technology, its performance can still be adversely affected by temperature variations, limiting workability and crack resistance even with increased dosage (such as in summer formulas). Some manufacturers address this issue by enhancing the degree of etherification in HPMC, enabling it to retain more water at higher temperatures.

 

Hence, the effectiveness of HPMC hinges on selecting and utilizing the right grade. Presently, there's a prevalence of unscrupulous practices among businessmen who adulterate HPMC, leading to poor quality. It falls upon corporate laboratory staff to ensure the selection of appropriate HPMC grades. Conducting experiments in the laboratory to ascertain the stability of mortar products is crucial for quality assurance.