I am going to be doing my first tiling project, a tub surround, around a jacuzzi tub. We have installed georgia pacific's wall board which is meant for tubs and resistant to molding and are getting ready to tile. The Board is set above the flange which leaves a 1" approximate gap at the bottom. What do you do with this gap. Do you fill it or just lay the tile over it? If you fill it do you just fill it with the thinset you are going to use to set the tiles? In the corners of the shower do you overlap the tiles by putting one tile up against the wall and the other over it so there is no gap? And, is the mortar caustic? I've read it can burn your hands. Please help. I am very nervous about doing it wrong because it is not easily fixed. My other half keeps assuring me this isn't going to be hard. I'm sure I'll feel more confident once I start, but I'd like some opinions on my post. Thanks.