How much do you know about redispersible latex powder?
Release Time:
2016-04-25
Source:
How much do you know about redispersible latex powder?
Regarding the dosage of redispersible latex powder in mortar, most customers are quite concerned. Below is a brief introduction: Redispersible Latex Powder It can significantly enhance the bond between mortar and the substrate, but it may also reduce the mortar’s water resistance. Hydrophobic agents can effectively improve the mortar’s ability to resist hydrostatic pressure, yet they may compromise its bond strength. Therefore, when formulating pre-mixed mortar products, it is essential to comprehensively evaluate the impact of each constituent on the mortar’s performance characteristics and, through experimentation, determine a cost-effective and technologically advanced mix design. Redispersible latex powder can markedly increase the mortar’s bond strength; the higher the dosage, the greater the improvement—yet compressive strength tends to decline, indicating the existence of an optimal dosage range. Given the relatively high cost of redispersible latex powder, increasing its content raises the overall cost of dry-mix mortar, so cost considerations must also be taken into account. High bond strength exerts a certain restraining effect on shrinkage, facilitating the dispersion and release of stresses induced by deformation; thus, bond strength plays a crucial role in enhancing crack resistance.
Studies have shown that the synergistic effect of cellulose ethers and latex powders is conducive to enhancing the bond strength of cement mortars. As the dosage of redispersible latex powder increases, the bond strength gradually rises. When the latex powder dosage is relatively low, the increase in bond strength becomes particularly pronounced with further increments in dosage. For instance, at a latex powder dosage of 2%, the bond strength reaches 0.182 MPa, thereby meeting the national standard requirement of 0.160 MPa. Taking putty powder as an example: the addition of latex powder can significantly improve the bond strength between the putty and the substrate. This is because the hydrophilic latex powder, together with the liquid phase of the cement suspension, penetrates into the pores and capillaries of the substrate; within these voids, the latex powder forms a film and adheres firmly to the substrate surface, thus ensuring strong bonding between the adhesive material and the substrate. This enhanced adhesion is also evident when scraping off the putty from the test panel—increasing the latex powder dosage does indeed strengthen the putty’s bond to the substrate. However, once the latex powder dosage exceeds 4%, the rate of increase in bond strength begins to slow down. It should be noted that the contribution to putty bond strength comes not only from the redispersible latex powder but also from inorganic materials such as cement and heavy calcium carbonate; therefore, the relationship between bond strength and latex powder dosage does not follow a linear pattern.
Water resistance and alkali resistance are critical performance indicators for determining whether a putty can be used as an interior water-resistant putty or as an exterior wall putty. When the dosage of redispersible latex powder is below 4%, the water absorption rate decreases with increasing dosage, and this effect becomes more pronounced as the dosage rises. Once the dosage exceeds 4%, the reduction in water absorption slows down considerably. The reason is that cement serves as the binding agent in the putty; without the addition of redispersible latex powder, the system contains numerous voids. Upon adding redispersible latex powder, the redispersed polymer emulsion forms a film within these voids, effectively sealing them and creating a denser surface film after the putty has been applied and dried. This dense surface film significantly inhibits water penetration, reduces water absorption, and thereby enhances the putty’s water resistance. When the dosage of redispersible latex powder reaches 4% or more, the redispersed polymer emulsion can essentially completely fill the voids in the putty matrix, forming a continuous, tightly packed film. As a result, the trend of decreasing water absorption levels becomes more gradual as the latex powder dosage increases.
Considering the effects of composite latex powder on bond strength and water resistance of putty, as well as its cost, a dosage of 3% to 4% is most appropriate, resulting in putty with high bond strength and excellent water resistance. The redispersed latex polymer from the latex powder effectively fills the voids within the putty matrix, forming a continuous film that thoroughly binds the inorganic components of the system with minimal porosity, thereby significantly reducing the putty’s water absorption.
