Tile adhesive options?
Swiss chemical giant Sika makes a (caulking gun) tube of tile adhesive that I've used for adhering large, very porous, travertine to painted sheetrock. In addition, I've seen 4ft. x 8ft. architectural limestone panels installed in office building lobbies and exterior facades using a strange gummy white paste that turns rock hard pretty quickly. It's stuck on the back of a panel like a snowball then squished into pancakes when the panel is rotated up into place against cinder block or cement.