Tile adhesive for bathroom wall

[Junk Gypsy]

Hi, I am about to put up some penny tile in my shower stall area in my Argosy and I would like some recommendations on what would be the best flexible adhesive to use so that it stays up and doesn’t crack off and come down. I have the proper grout that is flexible but I’m worried about the adhesive as most when dry become stiff and eventually brittle. Thanks in advance. Stay safe!❤️

[Al and Missy]

I installed a self-stick mosaic from Lowes. No problems so far. Sorry, no help on mastic.

Al