December 27, 2012
I think I would first ask the question "Why did it separate?" There may be some movement in the supporting structure, or in the tub itself, or maybe both. Even if there were some movement it may not be cost effective to tear the walls apart to fix the problem. So, I would definitely take off the original grout, if for no other reason but to be able to apply more of the new grout. This can be done with a Dremel if you happen to have one. The old grout may have mildew and dirt within it that you should try to get cleaned out. Clean the surface well for better adherence. Mix the grout to a paste consistency and apply, wipe with a wet sponge after a few minutes. I don't have any photos of this. All of my recent experience has been in remodeling my home and I took my bathroom walls down to the studs and reapplied Sheetrock. Good Luck.
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