When both redispersible polymer powder (RDP) and cellulose ether are present in wet mortar, some data models show that RDP has stronger kinetic energy to adhere to cement hydration products, while cellulose ether remains more in the interstitial fluid, primarily affecting the mortar’s viscosity and setting time. Cellulose ether has higher surface tension than RDP, so its greater enrichment at the mortar interface helps form hydrogen bonds between the substrate and the cellulose ether.
In wet mortar, as water evaporates, cellulose ether accumulates on the surface, forming a film within five minutes, which slows down further evaporation. As more water migrates from thicker areas of the mortar to thinner areas, the initially formed film partially dissolves. This water migration brings more cellulose ether to the surface, further enriching it. Thus, the film-forming properties of cellulose ether significantly impact mortar performance.
If the film is too thin, it may dissolve again, failing to limit water evaporation and reducing strength. If the film is too thick, the high concentration of cellulose ether in the interstitial fluid increases viscosity, making it harder to break the surface film when tiles are applied. Therefore, the film-forming ability of cellulose ether greatly affects open time.
The type of cellulose ether (e.g., HPMC, HEMC, MC) and its degree of etherification (substitution level) directly influence its film-forming properties, as well as the hardness and flexibility of the film.
