And then there's this from a home inspector: grout not caulk! grout not caulk where tile meets tub. His explanation makes sense: caulk traps moisture that's BEHIND it by not allowing it to evaporate. That moisture is coming from behind the tiled wall! Hence the puzzlement of why one can't clean caulk that appears to be sound. What's that gunk doing behind it and how did it get there? Everybody's concerned about caulking that seam to keep it waterproof from direct hits by shower water. (Why aren't people concerned about the wallful of porous grouted seams on tiled shower enclosures???--just that bottom seam....)
Caulk does keep shower water out, but that's not the problematic water. Shower water seepage through the porous grouted seams of the tiled wall runs down the back of the tiled wall and collects on the tub surface behind the caulked wall-meets-tub seam. (Or it continues downward causing damage to the ceiling of the room below.) With a grouted seam that won't happen cuz is porous and the moisture (from front and back) will evaporate. Yes, eventually the grout will age and crack from movement and need to be removed and replaced and again last for decades. Also a grouted seam looks better cuz matches the grout between tiles. While caulked seams fail yearly--now you know why--and get replaced repeatedly to remove the unsightly trapped gunk.
I just removed cracked grout (not a fun job) from the tub/wall seam that's been there since 1966 when the house was constructed. The last few years I've covered that seam with caulk only to have to replace it over and over again. Did I use grout this time? We're about to put the house on the market and didn't want the house inspector to report a fault in having grouted rather than caulked that seam and the buyers expecting that to be corrected. The tilt out there is pro caulk, not grout. So caulk it is. But when this problem comes up in our next house, we're going the grout route.
Q
getting grout out of cracks before caulking
Q