Redispersible latex powder
Redispersible latex powder is a spray-dried dispersion that forms a stable dispersion when added to water, with properties identical to the original emulsion. It is a commonly used dry powder mortar additive in putty.
1. The role of latex powder flexibility
In the production of building paint putty powder, redispersible latex powder is required. In a reasonable formulation, latex powder can increase bonding strength with a smaller addition amount.
From practical application experience, as a transition layer between exterior wall insulation and paint, the strength of the putty should not exceed that of the render mortar; otherwise, cracking may occur. Within the insulation system, the putty’s flexibility should exceed that of the substrate. This allows the putty to better accommodate substrate deformation and buffer deformation caused by external environmental factors, alleviating stress concentration and reducing the likelihood of coating cracking or peeling.
2. The Role of the Continuous Film After Drying
Redispersible latex powder is used in the production of putty powder. During production, the latex powder can be redispersed and re-emulsified. Due to the continuous consumption of water in the mortar (part absorbed by the substrate, part participating in internal mortar reactions) and the strongly alkaline environment provided by cement, the latex particles form a continuous, water-insoluble film in the mortar after drying. This continuous film is formed by the fusion of individually dispersed particles in the emulsion into a homogeneous mass.
During the application of putty, latex powder improves workability, enhancing the mortar’s scratch resistance and flexural strength, imparting plasticity to the mortar while reducing its hardness.
3. High compatibility between latex powder and cement-based materials
When redispersible latex powder is uniformly mixed into putty powder and then mixed with water, it forms a polymer emulsion upon contact with water. Through the initial hydration of cement, it gradually forms a cement gel. The liquid phase is saturated with Ca(OH)₂ formed during hydration, while the latex powder disperses into fine polymer particles and deposits on the surface of the cement gel/unhydrated cement particle mixture; As cement hydration continues, moisture in the capillaries decreases, and polymer particles are gradually confined within the capillaries, forming a compacted layer on the surface of the cement gel/unhydrated cement particle mixture and fillers; Under the combined effects of hydration reactions, substrate absorption, and surface evaporation, moisture content further decreases. During drying, the emulsion undergoes dehydration again, and the previously formed layered structures aggregate into a thin film, bonding the hydration reaction products into a complete network structure. The composite system formed by cement hydration and latex powder film formation enhances the dynamic crack resistance of the putty.
4. Latex powder can enhance overall strength
Adding redispersible latex powder to putty powder increases its strength and significantly improves hardness. It exhibits outstanding waterproofing performance, excellent bonding strength, and enhances the elasticity of mortar while providing a longer open time. Additionally, it confers superior alkali resistance to mortar, improving its adhesion/bonding properties, flexural strength, abrasion resistance, and workability. In flexible crack-resistant mortar, it also exhibits superior flexibility.