The role of redispersible latex powder in putty powder: it has strong adhesion and mechanical properties, outstanding waterproofness, permeability, and excellent alkali resistance and wear resistance, and can improve water retention and increase Open time for enhanced durability.

1. The effect of freshly mixed mortar

1) Improve construction.

2) Additional water retention to improve cement hydration.

3) Increase workability.

4) Avoid early cracking.

2. The effect of hardening mortar

1) Reduce the elastic modulus of the mortar and increase the compatibility with the base layer.

2) Increase flexibility and resist cracking.

3) Improve the resistance to powder falling.

4) Hydrophobic or reduce water absorption.

5) Increase the adhesion to the base layer.

The redispersible latex powder forms a polymer emulsion in contact with water. During the mixing and drying process, the emulsion is dehydrated again. The latex powder acts in the putty powder, and the composite system formation process of cement hydration and latex powder film formation is completed in four steps:

①When the redispersible latex powder is evenly mixed with water in the putty powder, it is dispersed into fine polymer particles;

②The cement gel is gradually formed through the initial hydration of the cement, the liquid phase is saturated with Ca(OH)2 formed during the hydration process, and the polymer particles formed by the latex powder are deposited on the surface of the cement gel/unhydrated cement particle mixture;

③ As the cement is further hydrated, the water in the capillary pores decreases, and the polymer particles are gradually confined in the capillary pores, forming a tightly packed layer on the surface of the cement gel/unhydrated cement particle mixture and filler;

④ Under the action of hydration reaction, base layer absorption and surface evaporation, the moisture is further reduced, and the formed stacking layers are aggregated into a thin film, and the hydration reaction products are bonded together to form a complete network structure. The composite system formed by cement hydration and latex powder film formation improves the dynamic cracking resistance of the putty.

From the perspective of practical application, the strength of the putty used as the transition layer between the external insulation and the coating of the external wall should not be higher than that of the plastering mortar, otherwise it is easy to produce cracking. In the entire insulation system, the flexibility of the putty should be higher than that of the substrate. In this way, the putty can better adapt to the deformation of the substrate and buffer its own deformation under the action of external environmental factors, relieve stress concentration, and reduce the possibility of cracking and peeling of the coating.