Redispersible latex powder (RDP) is an important dry powder additive used to improve the performance of dry-mixed mortar. Its working principle is mainly to enhance the key properties of mortar such as adhesion, flexibility, crack resistance and water resistance through processes such as dispersion, film formation and cross-linking.

1. Dispersion principle
RDP usually exists in the form of solid powder in dry-mixed mortar, and the surface of the particles is coated with a layer of protective colloid, such as polyvinyl alcohol (PVA), to maintain a stable powder state. After adding water, the protective colloid in the latex powder quickly dissolves, and the latex powder particles begin to redisperse, releasing small particle emulsions to form high molecular polymer particles dispersed in water. This dispersion process is similar to that of emulsions, but its characteristic is that through hydration, RDP can quickly return to the state of emulsions. Through dispersion, RDP can be evenly distributed throughout the mortar system, thereby enhancing the adhesion and anti-delamination performance between substrates.

2. Film-forming process
During the solidification process of cement or other inorganic materials, the emulsion particles dispersed by RDP will gradually lose water. When the water evaporates completely, the polymer particles dispersed by RDP gather together to form a continuous polymer film. This polymer film plays a “bridging” role in the mortar structure, connecting aggregates, fine powders and substrates together, significantly improving the bonding strength of the mortar. This layer of polymer film has a certain flexibility and toughness, and can adapt to the slight deformation of the base material, thereby improving the crack resistance of the mortar. In addition, the polymer film can also block the micro-pores in the mortar, reduce the water from entering the structure through the pores, and effectively improve the water resistance and impermeability of the mortar.

3. Molecular structure and reinforcement
The polymer main chain of RDP is usually based on monomers such as ethylene, ethylene acetate (EVA) or acrylate, and has excellent flexibility and adhesion. When the copolymers formed by these monomers are dried and dispersed, they can form stable polymer particles in water and eventually form a continuous film layer. This structure has strong adhesion and toughness, and can play a reinforcing role in dry-mixed mortar, improving its crack resistance, impact resistance and durability. By adjusting the monomer ratio, the performance of latex powder can be modified in a direction to meet the needs of different mortar applications.

4. Enhanced modification effect
RDP shows a significant modification effect in dry-mixed mortar, which is mainly reflected in the following aspects:

Improved bonding: After RDP is filmed, the polymer film can produce physical adsorption and chemical bonding with the surface of the substrate, which significantly enhances the bonding between the mortar and the substrate. Especially when used as an interface agent and tile adhesive, the effect of improving the bonding strength is particularly obvious.

Enhanced flexibility and crack resistance: The polymer film after RDP film formation is flexible and can absorb the tiny stress caused by external stress or temperature changes in the mortar, effectively reduce the cracks caused by shrinkage, and improve the crack resistance of the mortar.

Improved water resistance: The polymer film formed by RDP has a certain waterproof effect, which can reduce the capillary water absorption rate in the mortar and prevent moisture from penetrating into the substrate, thereby significantly improving the water resistance of the mortar. Therefore, RDP is widely used in mortars with high water resistance requirements, such as exterior wall mortar and waterproof mortar.

Enhance wear resistance and durability: The polymer film has good wear resistance, which can enhance the damage resistance of mortar under friction and impact conditions and extend its service life. RDP-modified mortar shows strong aging resistance under long-term outdoor exposure conditions, reducing environmental damage to mortar.

5. Comprehensive performance improvement and application
The application of RDP in mortar has greatly expanded the use scenarios of mortar. Due to its significant effects in improving bonding strength, enhancing flexibility and crack resistance, improving water resistance and impermeability, RDP is often used in a variety of dry-mixed mortar systems such as tile adhesives, self-leveling mortars, insulation board adhesives, plaster mortars and repair mortars. Especially in exterior wall insulation systems, indoor and outdoor decoration and repair projects, RDP has become one of the indispensable key materials.

6. Future development trends
With the development of the construction industry, the demand for green, environmentally friendly and energy-saving materials is increasing, and the application prospects of RDP in dry-mixed mortars are very broad. At present, environmentally friendly, low VOC (volatile organic compound) emission latex powder is becoming the mainstream of the market. Especially under the trend of sustainable development and resource conservation, RDP, which replaces some chemical raw materials with bio-based raw materials, is gradually becoming a hot spot in the market. In addition, the development of RDP products with high weather resistance and strong adhesion to meet the engineering needs under extreme climate conditions has also become a future research focus.

RDP obtains better adhesion, flexibility, water resistance and other properties by dispersing, film-forming and strengthening the structure in the mortar system.