Toilets, Sinks, Showers, Tubs and Disposals - Replacing the soap dish in the shower/tub????

I regrouted and recaulked the tile walls around my tub this weekend. I had pulled off some loose tile and cleaned the back of them and replaced them. the soap dish came off too and I used the tile adhesive to paste it back on. a day later, I removed the tape that was holding the soap dish to the wall and the soap dish fell off- the adhesive was still moist. so I re-did it and I'll let it sit for a few days.

question. the walls beneath the tile were regular drywall. when the tiles and soap dish came off, so did the paper thats one the drywall. I re-glued the tiles straight to the plaster surface of the drywall. Will that be a problem.

I know there should be some cement board or waterproofing back there but I really dont want to tear all the tile off and re-do it. Will the soap dish hold to the plaster when I remove the tape in a few days??

I used this white plastery looking adhesive from Lowes to put the tile and soap dish on the wall. This is what I used http://www.lowes.com/lowes/lkn?action=productDetail&productId=43951-1295-1040011-EA&lpage=none its called Mapei Floor and wall tile adhesive

If it falls off this time, get some thinset, mix it up to the consistency of peanut butter, clean all the surfaces of all the other stuff you have been using, butter the back and edges of the dish and install it in the hole, tape it up and wait a day. Good luck.