I built an outdoor tiki bar table. The top is ceramic tile over 3/4 inch pressure treated plywood. I used thinset to adhere and researched and found siliconized caulk to be the likely answer in place of grout as the table will reside outdoors, and it should remain flexible. I've worked with grout and caulk before, even silicone caulk. This was a nightmare. It tooled like complete crap. I'm disappointed as it was going well until this step and now it looks like it was done by a complete novice. (which I am.... Perhaps I'm just being overly critical, but can I remove it now? Would an unsanded been easier to tool? I don't want it shiny. Do I even have any options at this point?
The caulk will be the least of your worries, I believe. By rights that project is not gonna last very long I'm afraid to say. Is this ceramic tile a true porcelain? I imagine you used a modified mortar?
You should not have used pressure treated ply, plus you needed a concrete backer too. You do not use pressure treated for anything like this. Not sure what good pressure treated plywood is for.
TILE GUY - retired- TROY, MI - Method & Product suitability consulting.