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Redispersible polymer powder, commonly known as RDP, is a vital component in contemporary tile adhesives. It appears as a white or off-white water-soluble powder, produced by spray-drying a blend of synthetic polymer emulsion, protective colloid, and various additives. When integrated into dry mortar formulations, RDP enhances bond strength, adhesion, flexibility, water resistance, and workability.
1. Enhanced Adhesion: RDP improves the adhesion of tile adhesive to various substrates like concrete, gypsum board, wood, and metal. It forms a strong yet flexible film on the substrate's surface, promoting better bonding with the adhesive. This film enhances the wetting and spreading of the adhesive, preventing premature drying and cracking.
2. Improve workability: RDP can improve the workability and consistency of tile adhesives by reducing water demand, increasing plasticity, and reducing sagging. This is because RDP can act as a lubricant and a binder, which can improve the fluidity and cohesion of the mortar. Using RDP also reduces mixing time, increases open time, and improves the spreadability of the adhesive.
3. Increased Flexibility: RDP boosts the flexibility and deformability of tile adhesives, crucial for tiles and natural stones prone to cracking from thermal expansion, vibration, or movement. It enhances the adhesive's elasticity and tensile strength, reducing risks like delamination or detachment. This improvement in flexibility enhances the durability and longevity of the tiled surface.
4. Enhanced Water Resistance: RDP improves the water resistance of tile adhesive by decreasing mortar permeability and porosity. This prevents water, moisture, and salts from penetrating the substrate or tile, preventing staining, weathering, or decay. Additionally, RDP enhances the adhesive's resistance to freeze-thaw cycles, making it suitable for outdoor applications and cold climates.
5. Convenient Construction: RDP reduces dust, enhances adhesion and leveling, and minimizes shrinkage and cracking during tile adhesive application. This enhances construction efficiency and quality while reducing labor and material costs. RDP formulations can be tailored to meet specific requirements for different tile types, substrates, and environmental conditions.
One of the most significant uses of polymer-modified cement mortar is in the thin-layer construction method for tiles. The process involves mixing the packaged dry powder adhesive with water on-site. The mixed adhesive is then applied to the wall or floor using a scraper with rectangular teeth, and the tile is affixed before the adhesive dries. The adhesive must have good workability, a long open time, excellent slip resistance, and sufficient deformability to ensure durability under various climatic conditions.
In rigorous thermal curing tests, the stress development due to temperature differences and varying thermal expansion coefficients between the tile and the base layer is simulated. The internal stress is mitigated by the deformability provided by the rubber powder polymer distributed in the mortar system, preventing adhesive failure and tile damage. Highly porous ceramic tiles can theoretically bond to substrates with voids because cement mortar containing only mineral binders creates mechanical embedding in the interstices between the tiles and the substrate. This effect can be observed under an electron microscope.
For nearly non-porous tiles, the polymer ensures a strong bond to this near-glass material, as mortars containing only mineral adhesive-cement cannot bond such materials effectively. In these cases, the polymer provides almost all the bonding strength. This bonding mechanism is also applicable to other non-porous substrates.
RDP plays a crucial and versatile role in tile adhesives. It enhances adhesion, workability, flexibility, water resistance, and performance, thereby improving the sustainability of tiles. Incorporating RDP can also support the development of environmentally friendly and low-carbon building materials, benefiting both the environment and society. It is advisable to use high-quality RDP sourced from a reputable supplier and adhere to recommended dosing and mixing guidelines for optimal results.
