tiling onto plastic tub surround?
Can I apply Mastik or something directly to the fiberglass tub surround, or do I have to take out the tub surround, or do something else?
Re: tiling onto plastic tub surround?
It is not a good idea to tile on the tub surround. You should take out the surround (tub also if it's a 1-piece surround) and install a vapor barrier on the walls with cement board over that. You could also use Kerdi waterproofing over the cement board if you like. Make sure to use fiberglass mesh with thinset skimcoat at the corners if Kerdi is not applied. Hope that helps.