Geoffreys almost got it. In the professional world, I would make it right starting with removing this and doing it correct from framing thru to waterproofing You have the wrong tub to start and the Flange needs to be be properly lapped and the waterproofing tied into it or you will have issues in time. You need the durock to be graded toward the tub, lapped over the flange and either A moisture barrier siliconed to the flange under the durock (which is a piss poor approach when you consider putting screws thru the moisture barrier on a tub deck but it is still accpeted as a practice.) *The smarter way is to use a topical membrane that ties into the tub deck with A proper sealant that will lap the tub/durock joint and stop durock from wicking.. Also read the durock installation specs in regards to screw courses.and framing specs. If im in somebodys home accepting payment *Thats how its done..but we are on the web here....do as you wish..

Heed MillWorkman's advice. Any change of plane, whether it is wall to ceiling, wall to floor, wall to wall, etc.. will almost always require caulk of some sort. !00% silicone for anything around water. In other areas, a siliconized caulk, or paintable 100% silicone caulk can be used. I have done a lot of painting, either for myself or others, and I learned from an experienced pro to put a light layer of caulk in corners, around mill work, and wall to wall/ceiling/floors to prevent the paint from cracking/splitting. Just my 2 Lincolns worth.

If you're going to use tiles at the edge to form a water resistant barrier, I see no need to fill in behind them. The tiles you install are unlikely to be as thick as the old baseboard. How will you address the gap between the floor and the new tile base? Perhaps a better choice would be to install PVC baseboard and seal the edges with a sanded caulk to match the tile grout color. Unless you have a drain in the floor, making the room a drip pan will only work until there's a leak big enough to flow out the door.

thanks mainenell. Any suggestions on the type of caulking, Im sure once I go to Lowes or HD, there will be so many types and brands with minor and major differences, I will get lost. Most frustrating thing about a DIY project is to pick an item at these big box stores. Is this the current one grout?