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As part of the cosmetic updates for the bath, I decided to remove the moldy caulking where the tile meets the bathtub. It looks like the previous owner put the caulk over the grout, I'm assuming because it had cracked. When I stripped the caulk, I got an uneven line of old grout with varying depth and still with mold spots here and there. Looking online, the consensus seems to be that the tile edge at the bathtub needs to be caulked, not grouted, so I figured I would need to remove the old grout anyway whether I would re-grout or caulk.

I tried removing the grout with the grout saw but this was very tedious and there were also some tiles with a gap thinner than the saw. So I used Dremel with a 1/16 carbide bit to make ~3mm deep groove - this went faster - however because of the work angle in the corners I cut into the tile in some areas resulting in a gap as much as 1/8" (see the pic).

At this point I'm thinking that re-grouting is out of question since the tile edge is uneven; I could use caulk and get a straight line but wouldn't I still eventually get the mold behind the caulk?

  • Would I have to clean out all old grout from the groove before caulking? The groove is ~3mm deep.
  • Would sealing (with a grout sealer) whatever grout is left in the groove and caulking over it help with reducing mold growth? The shower will likely be used daily.

The rest of the grout/tile is in a good condition. What is my best course of action from here?

cut tile

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  • I would clean the old grout to the solid base and leave no loose part, then seal with mildew-resistant silicone sealant. Re-seal if getting mold again.
    – r13
    Jan 7, 2022 at 0:10
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    Mold is a sign of moisture. Bathrooms are moist by nature but normally they have fans to exhaust the moisture and pull in dry air preventing mold from growing. In the winter we place a box fan to blow into the shower room for about an hour after a shower, it dries it and puts the moisture in the house which needs it during heating season.
    – Gil
    Jan 7, 2022 at 1:58

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It's not necessary to remove the grout from under the bottom of the tile (it's not ideal from an expansion and contraction point of view, but that is another matter). As long as you have a 90 degree clean area between the tile and the tub, you are okay to reapply new silicone. Buy the best you can find and thoroughly clean the surface before applying. Try to get a good angle and don't feather out the edges too much. Best silicone sealant profile

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