Why is redispersible latex powder added to self-leveling mortar?
Release Time:
2020-05-29
Source:
Why is redispersible latex powder added to self-leveling mortar?
Due to the unique characteristics of self-leveling floor construction—namely, that the self-leveling layer is a secondary overlay, typically applied at a thinner thickness than conventional floor screeds, and often subjected to minimal or no curing after placement in order to expedite project delivery—the self-leveling layer must withstand thermal stresses arising from differing materials. In some cases, self-leveling materials are used on substrates that are inherently difficult to bond to. Therefore, even with the aid of an interface primer, incorporating a certain amount of latex powder is essential to ensure long-term, robust adhesion of the self-leveling layer to the substrate. Whether applied to absorbent substrates (such as commercial concrete), organic substrates (such as wood), or non-absorbent substrates (such as metals, e.g., ship decks), the bond strength of the self-leveling material increases markedly with increasing latex powder content. For instance, in failure-mode tests, bonds involving self-leveling materials containing latex powder consistently fail within the self-leveling layer itself or within the substrate, rather than at the interface, thereby demonstrating excellent interfacial adhesion.
Although the wear resistance requirement for the self-leveling underlayment is lower than that for the top layer, the floor inevitably experiences various dynamic and static stresses—such as those imposed by furniture casters, forklifts (e.g., in warehouses), and vehicle wheels (e.g., in parking lots)—making adequate wear resistance one of the key properties that ensure the long-term durability of self-leveling floors. Increasing the dosage of latex powder leads to a very significant improvement in the wear resistance of the self-leveling material; in contrast, self-leveling materials without latex powder, after 7 days of laboratory curing, exhibit complete substrate exposure after only 4,800 reciprocating roller passes. This is because latex powder enhances the cohesive strength of the self-leveling material and improves its plasticity (i.e., deformability), enabling it to effectively dissipate dynamic stresses transmitted by the rollers.
The addition of latex powder enhances both the tensile strength and the elongation at break of self-leveling floor coatings. As the latex powder content increases, the cohesive strength (tensile strength) of the self-leveling material improves markedly, while its flexibility and deformability also increase significantly. This is consistent with the fact that the tensile strength of latex powder is more than ten times that of cement. Experimental results show that when the dosage is 4%, the tensile strength increases by over 180% and the elongation at break increases by over 200%. From a health and comfort perspective, this enhanced flexibility helps reduce noise and alleviates fatigue associated with prolonged standing on the material.
Under conditions of constant water-to-cement ratio and air content, the dosage of latex powder has a significant influence on the flexural and compressive strengths of cement-based floor screeds. As the latex powder content increases, the compressive strength decreases slightly, while the flexural strength increases markedly, resulting in a gradual reduction in the compressive-to-flexural strength ratio. This indicates that the brittleness of self-leveling floor materials decreases substantially with increasing latex powder content. Consequently, the elastic modulus of the self-leveling material is reduced, and its crack resistance is enhanced.
Self-leveling mortar products are complex, and their various performance characteristics can be significantly enhanced through the addition of latex powder. Latex powder plays a crucial role in increasing the tensile strength and flexibility of self-leveling floor materials, as well as improving their bond strength to the substrate. Incorporating redispersible latex powder can also improve the water retention of fresh cement mortar, while enhancing the hardened mortar’s bond strength, flexibility, impermeability, and corrosion resistance.
