I'm installing some large format (406mm x 406mm) 12mm travertine tiles on some walls in a bathroom. I'd like to finish some exposed tile edges within some aluminium tile trim. However, I'm unsure which depth of trim to go for. Clearly it'll need to be at least 12mm but I have no idea how thick the adhesive will be after bedding the tile down. The adhesive is 'Vitra marble and stone select' and the recommended trowel notch size is U9 or E10. What would be an appropriate trim depth so that I can have the surface of the tile level with the trim?
I would experiment a bit using some cutoffs and a steel combination ruler. Try to figure the average float percentage, I would expect 10-30% of the notch height for tiles that large.
The depth of mud under tile is variable, mostly based on the wall flatness and somewhat based on tile size. You have to float enough to bridge and give full support, more so with a natural stone tile like travertine.
Your edge profile will look best and protect best if its as flat to the wall as possible.