How do premixed mortar additives improve mortar performance?-HPMC/RDP/VAE

HPMC can be used as a thickening and water-retaining agent for mortar in construction, while RDP/VAE can be used as a toughening agent for mixed mortar, making mortar application easier. Shijiazhuang Cellulose Co., Ltd., as a Chinese cellulose company, can provide you with high-quality industrial-grade chemical powders HPMC/RDP/VAE.

I. What is Premixed Mortar? Why are Additives Needed?

Premixed mortar (dry-mixed mortar) is mortar that has been precisely batched and uniformly mixed in a factory, then transported to the construction site in dry powder form. It only requires the addition of water and mixing according to the specified ratio before use. Compared to traditional on-site mixed mortar, it offers advantages such as stable quality, environmental friendliness, and high construction efficiency.

However, to achieve these advantages and meet various complex construction requirements (such as thin-layer construction, high bond strength, and construction in inclement weather), basic components such as cement and sand alone are far from sufficient. This is where additives play the role of "magic powder." They are added in extremely small amounts (usually 0.1% to 5% of the total mortar mass), yet can significantly improve and adjust the mortar's performance.

II. Detailed Explanation of Core Additives: How Do They Improve Mortar Performance?

The following are some of the most critical and commonly used premixed mortar additives and their mechanisms of action:

1. Cellulose Ethers - Mortar's "Water-Retaining and Thickening Agent"

Representative Product: Hydroxypropyl Methyl Cellulose Ether (HPMC) is the most commonly used.

Core Mechanism of Action:

Water Retention: HPMC molecular chains can adsorb a large number of water molecules, forming a hydrated film. In mortar, this film effectively prevents water from being absorbed too quickly by the substrate (such as bricks or concrete) or evaporating into the air. This ensures that the cement has sufficient water for a complete hydration reaction, thereby achieving the final strength.

Thickening: The long molecular chains of HPMC become entangled in aqueous solution, greatly increasing the viscosity of the mortar, thus improving the workability and anti-sag properties of the mortar (i.e., the mortar will not easily slide down vertical surfaces).

Improved Performance:

Enhanced Bond Strength: Good water retention ensures sufficient cement hydration, resulting in naturally high strength.

Prevents cracking: Slows down water loss, reduces drying shrinkage stress, and minimizes plastic cracking.

Improves workability: Makes the mortar smoother and more manageable, reducing plastering effort and increasing work efficiency.

Extends open time: The mortar remains workable in the container for a longer period and is less prone to drying out.

2. Redispersible latex powder – the “strong adhesive” and “toughening agent” of mortar

Representative products: Vinyl acetate-ethylene copolymer powder (VAE), etc.

Core mechanism of action:

Film-forming adhesion: After the powder is dispersed in water, as the water evaporates and the cement hydrates, a polymer film forms on the pores and particle surfaces of the mortar. This film acts like an ubiquitous “spider web,” firmly binding cement hydration products, aggregates, etc., together.

Enhanced cohesion: The polymer film itself is flexible, which can greatly improve the flexural strength and toughness of the mortar.

Improved performance:

Significantly improved bond strength: Especially crucial for difficult-to-bond substrates (such as insulation boards and smooth concrete surfaces). This is a core component of tile adhesives and insulation system mortars.

Improved flexibility and impact resistance: Enables the mortar to withstand certain deformations and impacts without cracking.

Lower elastic modulus: Makes the mortar “softer,” better adapting to the thermal expansion and contraction of the substrate, reducing stress cracking.

Improved impermeability: The polymer membrane blocks some of the capillaries, increasing the density and water repellency of the mortar.

3. Air-entraining agents - "air-entraining plasticizers" and "antifreeze agents" for mortar

Representative products: Alkyl sulfonates, saponins, etc.

Core mechanism of action:

Introducing microbubbles: Air-entraining agents are surfactants that reduce the surface tension of water, stably introducing a large number of uniform, closed microbubbles (approximately 0.01~0.1mm in diameter) during mortar mixing.

Improved performance:

Improved workability: These tiny "balls" greatly improve the lubricity and plasticity of the mortar, making construction easier. Under the same workability, the amount of mixing water can be reduced.

Improved freeze-thaw resistance (key role): When the mortar freezes, these microbubbles provide a buffer space for ice crystal expansion, preventing the internal structure from cracking. This is an essential property for winter construction and exterior wall plastering mortars.

Reduced density:Introducing air makes the mortar lighter.

4. Water-repellent/Waterproofing Agents - The "Raincoat" for Mortar

Representative Products: Organosilane powder, stearates, etc.

Core Mechanism of Action:

Capillary Hydrophobicity: The molecular structure of these substances has one end that is hydrophobic (friendly to organic matter) and the other end that is inorganic. The inorganic end anchors to the surface of cement and sand, while the hydrophobic end faces outward, forming a water-repellent film on the inner wall of the capillary. When water attempts to penetrate through capillary action, it is blocked by this film.

Improved Performance:

Excellent Impermeability: Gives mortar a "breathable" waterproof function, meaning liquid water cannot penetrate, but water vapor can escape, preventing condensation and mold growth on the wall.

Improved Weathering Resistance: Reduces rainwater erosion and freeze-thaw damage to the mortar.

Prevents Efflorescence: Reduces water penetration, thus reducing the possibility of internal soluble salts being carried to the surface.

5. Starch Ethers - Mortar's "Anti-Sagging Agent"

Core Mechanism of Action:

Thixotropy: Starch ethers significantly increase the structural viscosity of mortar (i.e., its viscosity at rest), but once subjected to shear forces (such as stirring or troweling), the viscosity rapidly decreases, restoring its fluidity. This property is known as "thixotropy."

Improved Performance:

Excellent Anti-Sagging Properties: Particularly suitable for thick-layer plastering mortars and tile adhesives, preventing sagging even when applied to ceilings.

Enhanced Workability: Works synergistically with cellulose ethers to make the mortar more "smooth" and less sticky to the trowel.

6. Water-reducing agents/plasticizers - the "lubricant" of mortar

Representative product: Polycarboxylate superplasticizer (PCE).

Core mechanism of action: Electrostatic repulsion/steric hindrance: Water-reducing agent molecules adsorb onto the surface of cement particles, creating a strong repulsive force between the particles, thereby releasing the water trapped in the flocculated structure, achieving a "lubricating" effect.

Improved performance: Significantly reduces water consumption while maintaining the same fluidity (water reduction rate can reach 20%~40%). This is the core of high-performance mortars (such as self-leveling mortars and high-performance tile adhesives).

Increased strength and density: Lowering the water-cement ratio is the most effective way to improve the strength and durability of cement-based materials.

Improved fluidity and self-leveling properties.

7. Retarders and Accelerators - The "Time Controllers" of Mortar

Retarders (e.g., sodium citrate, gluconate): Delay cement hydration, extending the workable and open time of the mortar, suitable for construction in high-temperature seasons or large-area construction.

Accelerators (e.g., lithium carbonate, aluminate): Accelerate the cement-water mixture, allowing the mortar to set and harden quickly, often used for repair mortars requiring early strength and rapid setting, or for winter construction.