Achieving superhydrophobicity with an epoxy/ZnO coating can be challenging, even with stearic acid treatment. One possible reason for the lack of superhydrophobicity could be incomplete coverage of the surface with the coating, which can result in regions of the surface that are not hydrophobic. Another possibility is that the surface roughness of the coating is not sufficient to create the necessary micro- and nano-scale features that contribute to superhydrophobicity. To address these issues, one could consider optimizing the coating process to ensure complete coverage and increasing the roughness of the coating by modifying the deposition conditions. Additionally, using a different material or modifying the surface chemistry of the coating could also be explored.

I guess the Zno is only for giving a rough texture. If it is washed away it will turn into a simple epoxy coating. Because if you try to mix the zno with the epoxy, epoxy will cover the rough surface of zno with itself, making a polished coating with less hydrophobicness.