Some of your questions are not straightforward that is why you get some of the answers you are getting . We as tilers rely a lot on what we are told by adhesive manufacturer's and that combined with experience is what we make our choices on . I can't remember what the exact differences between an s1 or s2 adhesive are but I know what I would use them for so when you ask a question and you are told what adhesive you should use your answer is your answer
