Catbuilder, I don't know the answers to most of your questions, since I did not do the work, nor did I witness the work done. He did not show me the type of caulk (he does this for a living--I trusted him to use what was appropriate). He did not report seeing any visible mold (I asked.) There was no delay between removal and recaulking. It dried for at least 24 hrs, maybe a little longer--I cannot recall. I presume the surround was *adequately* waterproofed, but again I did not do the work. I saw that they did do the waterproofing.

Could be a couple of things. Silicone caulk, when removed, can leave a residue that makes it difficult for other applications of caulk to adhere to. There are "caulk residue removers" available at box stores, that might help. "Liquified caulk" is usually a sign of 100% latex caulk that undergoes long-term water exposure. This exposure could be either from standing water on the edge of the tub after showering, or from water coming down the "back side" of the tile, or down the drainage plane, and hitting the caulk. If the caulk is mushing out just due to direct water spray and standing water on the edge of the tub, then going with a siliconized-latex caulk will give you better water resistance. 100% silicon has the best water resistance of all, but it can be a bit messy to install and tool. As to not caulking that joint, if the drainage plane (usually 6-mil polyethylene or tar paper) that is behind your tile backer board overlaps the flange on the edge of the tub, you might be okay.

Anytime you have a "change of plane" as you do here...you MUST caulk it. Dig out the grout by the tub. You need to caulk this area. A silicone or urethane caulk is best....but needs to be cleaned up with denatured alcohol. Here's the trick: Fill the tub 3/4 full of water before caulking it. This approximates the weight of the water and a person. When you caulk it, the tub is as low as it will be. Might require some gymnastics or a bathing suit...but the idea is that, rather than the caulk pulling away when filled...it cures at the lower expansion and "rolls" up a bit when empty, thereby not allowing it to seperate when filled. Hope this helps.....

As far as I am aware, silicone is caulk. There is caulk that is acrylic and caulk that is silicone. In both my bathrooms I used Laticrete silicone caulk for change of planes on my tile. It is matched to my Laticrete grout that I used. Find out what brand grout & color you used and buy the matching silicone grout that the manufacturer offers. When I had contrasting colors between surfaces I choose the color caulk that matched the least level or straight surface. For example my toilet was white and my floor dark. The floor was somewhat rustic and rippley. The toilet was real smooth and straight edged. I used a dark caulk to highlight the clean white edge. If I would have used white, the white would have highlighted the ripply floor surface, which I didn't want to do. I used blue painters tape to line the surfaces before I caulked. Making sure the tape was really close to the edges. I caulked, then ran my finger over the caulk to get a nice finish. I used alcohol on my finger as I ran it along the caulk. I wouldn't spray anything first, before the caulk, as it might make it not stick to the inner tile edge surfaces. Pull the tape right away, before the caulk sets. I would use alcohol on a paper towel to clean up any stray caulk. I know others have said that windex works too. I am no expert, only a few DIY jobs. But this worked for me. There are many great people on this forum that can help.