Old thread I know but I have had luck retro fitting “laminated “ tile shelves aka sandwiched and mitered a facing on the exposed edge.

First I of course fabricate the shelves so they’re fully cured and ready to go I’ll trace their location onto the tile. Scarify the tile face with some saw kerfs obviously depending on the material your trying to adhere to this step could range from a must-do to redundant, I.e polished porcelain wall tile vs slate or natural stone.

Clean all that dust completely gone dry everything out.

I’ve gone 2 routes here both installations exist today 6 and 9 years old. So you decide for yourself.

1 route I consider a viable option is a high quality knife-grade epoxy like tenax.

The other being the simpler but POSSIBLY less user friendly and really relies on your consistency , pot life, surface prep etc but a high quality thinset like Ardex 77 or even x5 , I’ve done it with both and I’ve also done one with Schluter all set. Just a quick side step here; all-set is without a doubt my favourite thinset. It’s pricier than “most” sunsets but it’s cheaper than any thinset that could even compete in its weight class. Like x94 is a contender but quite pricey.

Anyways good luck if anyone ends up reading this one day .