It’s not really fair to compare organic mastics to thinset mortars, because mastics occupy a particular niche in the industry and should be used only within very specific parameters.
Shower pans and pan liners may not seem to be a very interesting subject for discussion. First of all, one cannot see them once the installation is complete. And then, because they are out of sight and mind, you tend to forget about them. That is, until problems surface in the form of odors, drain blockage and bacteria growth.
Questions often arise regarding what constitutes a suitable substrate to which ceramic tile can be bonded. A number of sources can help you determine whether or not your surface is suitable and also advise you on how to prep these surfaces.