It was time to re-caulk my bathtub, due to mold/mildew in the surface.

The walls are tile down to just above the bathtub and the plumber had apparently used a clear caulk over grouting. I successfully removed the clear caulking, but then some the "grout" pulled out. It's almond colored, but still soft and flexible. My best guess is it's either a colored caulk or a putty.

At this point I think I have the following options:

  • Fill the gap with an almond caulk then top it with fresh clear caulk
  • Just completely fill the gap with a clear caulk
  • Fill the gap with a backer rod then caulk over it
  • Completely fill the gap with white caulk

The problems I see

  • The wall tiles are thick, so the gap is deep, but it's not tall (less than 1/8") - which will make backing rod hard to get in there.
  • I probably need to spread the caulk a little to either side of the gap/join to ensure it's water-tight.
  • Using a White caulk will look bad spread up the tiles, and using a colored caulk will look bad spread across the white tub top
  • Using a colored caulk behind clear will make it look like grouting in the gap but
    • I'm not convinced the clear caulk will adhere to the colored stuff (this may be why they had spread it onto the bath and tiles).
    • I don't how long (or whether) to let the colored caulk dry before applying the clear
    • I've managed to lay my hands on silicon colored caulk to go with the silicon clear, but only the clear caulk is mold-resistant.
  • Fill the deep gap with clear caulk will obviously look opaque ... and I'm not sure how it will look in the end.

And, obviously, a heavily used bath/shower is out of action while it all completely cures.

Suggestions desperately welcomed!


Here's the "grout" that was behind the clear silicone

enter image description here

  • 1
    I think you're focused a little too much on the appearance of the fill material. For starters, forget about clear caulk ... it just moves the problem to whatever is behind it, and in reality you shouldn't care what's behind it .. you don't need anything behind it. Think from the perspective of a user of that bath and not someone intent on analyzing the caulk line. If you can do that, all you need is to pick the wall or tub color, seal the gap, and you're done.
    – jay613
    Commented Apr 30, 2022 at 21:33
  • So, any ideas what they'd put behind the clear caulk instead of grout? It's not sanded, and it's not putty. It's still flexible after 4 years and can be pulled apart
    – kdopen
    Commented Apr 30, 2022 at 22:29

2 Answers 2


You don't need clear caulk and you don't need a backer for a 1/8 inch gap. Just use silicone caulk with a bead big enough to cover the gap and adhere to both the tub and wall, and you're done.

I'd use white, to match the bath but if you prefer you can try to match the wall color. The transition between colors has to be somewhere ... you just need to pick where and IMO, a colored caulk will draw more attention. People are used to seeing a white bath with a white caulk bead, and they won't take a magnifying glass to it, they'll just bathe.

Re filling the gap: You only need to fill the gap with a backing rod or grout if it is too big to just lay silicone caulk over it. I don't know exactly what "too big" is but yours, 1/8 inch, is not too big. You don't have to fill the gap with silicone, it's not like grout that fills the gap between tiles. The silicone makes its seal on the outer surfaces of the tub and tile, even if there is no gap. If there is a small gap you can shove it in a little, it adds strength but it does not have to fill it.

  • I agree, white tub, white caulk.
    – JACK
    Commented Apr 30, 2022 at 22:21
  • 1
    "People are used to seeing a white bath with a white caulk bead, and they won't take a magnifying glass to it, they'll just bathe." ... not worried about the people using it, I'm worried about the one who will decide whether or not I did a good job. She will take a magnifying glass to it :)
    – kdopen
    Commented Apr 30, 2022 at 22:24
  • 4
    Use purple caulk, then when she doesn't like it, peel it out and replace with white, which will then seem perfect!
    – RetiredATC
    Commented May 1, 2022 at 1:19
  • 1
    @kdopen this isn't marriage.stackexchange but since you "asked": Ask her to choose a strategy. Then you come here and ask us about how to execute it best. If she chooses clear caulk with gold flakes mixed in over a light up LED rope that you shove in the crack .... GREAT. Just figure out how to ace it. Hopefully she'll choose white caulk and then .... youtube is your friend.
    – jay613
    Commented May 1, 2022 at 12:33
  • 1
    I added a note to the answer about filling the gap.
    – jay613
    Commented May 1, 2022 at 12:45

I buy a caulking that is close to the color of the original grout. I apply it, smooth it to a groove as close as I can to the original seams. Usually I tape both sides so the edges are perfectly straight. As soon as I apply and smooth the caulking I sprinkle or blow grout onto the wet caulking - a much as it will hold. Then immediately pull off the tape. Leaving it on will cause the cured caulking to also pull off with the tape. You will now have a joint that not only looks like grout but IS on the surface. Using this method on counter to tiled backsplash joints eliminates future cracking when the counters and/or walls move ever so slightly as the caulking is flexible.

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