Views: 27 Author: Site Editor Publish Time: 2025-04-03 Origin: Site
With the continuous improvement of environmental protection requirements and construction quality standards, high-efficiency additives are increasingly widely used in dry-mix mortar. These additives not only significantly improve key properties of mortar such as workability, water retention, and strength but also play an irreplaceable role in saving cementitious materials, reducing project costs, lowering energy consumption, and ensuring project quality. The following are several common types of additives in dry-mix mortar and their characteristics:
As an important organic additive, redispersible polymer powder performs excellently in fields such as thin-layer plastering mortar, tile adhesives, external wall insulation systems, and self-leveling floor materials. It forms a "dual bonding system" with cement in mortar, enhancing the bonding performance of mortar through synergistic effects. At the same time, it can effectively improve the workability of mortar, increase the flexural-compressive ratio and tensile-compressive ratio, and enhance the mechanical stability of mortar. With the increase of polymer powder content, the dry bulk density of mortar increases accordingly, thereby endowing the modified mortar with good wear resistance and impermeability, and expanding the application scenarios of mortar.
Cellulose ether provides excellent water retention capacity for mortar through intermolecular forces, effectively solving the problem of rapid water penetration or evaporation during thin-layer application, and ensuring uniform and sufficient hydration of inorganic binders such as cement and gypsum — thanks to its heat of vaporization similar to that of water and capillary diffusion characteristics. In the mortar system, cellulose ether acts as a plasticizer, reducing the frictional resistance between particles, playing a lubricating role, improving the workability of mortar, and reducing the risk of cracking during thick-layer application. In addition, cellulose ether swells in volume after dissolution, increasing the viscosity of the slurry through bridging, which can effectively inhibit the settlement and stratification of fine aggregates and cement particles, improve the uniformity of mortar, enhance the bonding strength with the base material, and significantly reduce shrinkage deformation.
The core function of water reducers is to reduce the water demand of mortar through plasticizing effect. Under the premise of maintaining the same workability, the water reduction rate increases with the increase of admixture dosage. At the same time, the dispersing and moderate air-entraining effects of water reducers have a positive impact on improving the water retention of mortar, so they are widely used in scenarios with high fluidity requirements such as self-leveling，surface mortar, and leveling mortar. At present, there are three main types of water reducers commonly used in dry-mix mortar: casein, as a natural superplasticizer, has outstanding performance in thin-layer mortar, but its quality and price fluctuate greatly due to its natural properties; melamine formaldehyde condensate has good plasticizing effect, but its role in thin-layer mortar is limited, and there is a problem of formaldehyde release; polycarboxylate water reducer, as a new generation of technical products, not only has excellent efficiency but also no formaldehyde release, making it the preferred choice for both environmental protection and performance.
Hydrophobic agents represented by organosilanes and their modified compounds play a role by virtue of the active reactive groups in their molecules. In the highly alkaline environment formed by cement hydration, the hydrophilic organic functional groups of silanes hydrolyze to form highly active silanols, which then undergo irreversible reactions with the hydroxyl groups in cement hydration products to form stable chemical bonds. This bonding makes the hydrophobic organic functional groups face the outside of the pores, endowing the pore surface of the mortar with hydrophobicity, thereby achieving an overall waterproof effect.
The addition of finely dispersed organic polymers will increase the porosity of mortar, so defoamers need to be used to eliminate bubbles. The commonly used powdery defoamers in dry-mix mortar are based on chemical groups such as polyols and polysiloxanes, and there are also types such as hydrocarbons, stearic acid and its esters, and tributyl phosphate adsorbed on inorganic carriers. High-quality defoamers need to have good chemical stability, surface tension lower than that of the medium to be defoamed, and insolubility. Their role is not only to adjust the bubble content but also to reduce mortar shrinkage. It should be noted that the effect of defoamers is system-specific; a component that acts as a defoamer in one system may have an air-entraining effect in another system. Therefore, it is necessary to select special or composite defoamers for different mortar systems.
