I have several tiles that have popped off or were loose that we have removed around the spa area of my pool. I have cleaned off the backs of all of the tiles and the concrete. I think the pool will need to be remodeled (tile and plaster) in the next year or so, but I am hoping to make it a little longer before spending that kind of money. What can I use to glue the tiles back? I am assuming I need to use a thin set mortar and grout, but does it need to be a something special designed for pools/outdoor use? Thank you all so much for your help!!