How to grout bathroom tub / tile joint?
Hello. I'm trying to fix worn out grout above my bathroom (white porcelain) tub. I dug out much of the old grout, and 1/2 of the botom tiles came out in the process. This row of tiles is cut to only about 3/4" high, and 4" wide. The spacing between tiles is 1/16", and 1/4"-1/2" between the tiles and the tub. Behind some tiles is a bit of the backing wood wall, and only empty space behind others. So, there's not much solid substrate behind. I've repositioned some tiles by gobbing in 'SimpleFix Pre-mixed Adhesive & Grout, for grout joints 1/16" to 3/8"' behind them on the tub, the bit of backing available, and between the new tile and it's neighbors, but not filling in all the way so i can do a surface grout after it sets (I thought it might shrink and not work if I filled in, adhered the tiles, and grouted all the way in one step.) For the tiles with only air behind them, I glued in thin 3/16" strips of wood onto the riser beams behind so that tomorrow I'll have something to glue/grout the tiles onto.
My questions are:
1. The "Adhesive & Grout" stuff is sandy, will I damage the porcelain (I think) tub, or the ceramic (I think) tiles?
2. Is this "adhesive & grout" a good grout for the 1/16" gap between tiles (I read it shouldn't be sanded), or the wider gap between the tiles and tub? (The ingredients are silica quartz, limestone, acrylic copolymer, water.) I read that normal grout wasn't flexible enough or doesn't bond the tub well enough to use at the tub/tile joint. If I should use caulk, what kind? My old silicone surface fix was getting moldy behind.
3. How about the joint where 2 walls come together? The existing had silicone behind caulk.
I have a few tiles that seem solidly in position now, but I have more to put in, and haven't grouted/caulked yet.
If anyone's actually read this, my thanks, and any responses are appreciated.