1 year ago I remodeled my bathroom.

Tile guy did a cheapo job. After the fact, I used a clear silicon to line the edge between the tile and the tub.

Now I see this deterioration of the grout at the tubs edge.

What is causing this?


  1. This is on an exterior wall.
  2. Wall has insulation, Durock, AquaBan coating and taped edges.

enter image description here

enter image description here


It is probably failing because grout was in the gap prior to you caulking over it and it was not clean enough.

The gap should not have been grouted at all. You should remove all of the caulk and grout, use a retractable utility knife and a five in one tool to clean it out. Use the flexibility of the knife to get as much of the old caulk out of the gap and off of the tub lip. (protect the tub lip with some painter tape) Clean the gap well with some denatured alcohol and 3M scouring pad and dry with a towel. (It is vital that you get all of the old caulk off.)

It should be filled with 100% silicone, mold/mildew resistant, caulk. Tape off the tile and the tub with painters tape so that just the thin gap that you want caulk to be is exposed and then apply the caulk with caulk gun.

There are many tutorial videos on YouTube that will give you instruction on this technique; How to caulk a tub YouTube search.

Here are two

Ask this old house.

See Jane drill.

  • It's not grout... I am curious what it is though. – DMoore Feb 1 at 4:26
  1. Too big of a gap between the tub and the tile.
  2. Using grout at that interface.

The tub, sitting on the floor, is going to move relative to the tile (attached to the wall), especially when water is added to the tub. Whatever is used to seal that area needs be an elastomer, like GE Silicone II (just one of many products available). But they are limited in how wide a gap they can seal.

Here's picture of my tub/tile interface before it was caulked. Gap is 1/6" to 1/8" all the way around.

enter image description here

  • There is nothing wrong with grouting here. Do it all the time. You can always apply silicone over that grout and the silicone performs much better (if what gets behind it, it dries instead of instant mold and silicone coming undone. – DMoore Feb 1 at 4:28

I've seen similar gaps in caulk around tubs. It may not be the same as your tub, but it was caused by the floor shifting from water damaged joists.

It could also be the quality of the caulk and/or how it was applied. If it was applied unevenly without fully filling the gap the thinner area can shrink and open up. This is also due to low cost/quality caulking.

Other possibilities are there was soap film on the surface that didn't allow the silicone to adhere, the caulk hadn't cured fully before it was subject to water, and the gap was to wide for the caulk to fll in one pass.

The repair is to cut out the old dried caulk being careful not to cut any deeper than needed (there may be felt membrane behind the tile). Vacuum out the loose pieces. Lay down some blue tape for a boarder and re-apply 100% silicone. Allow to dry for the prescribed length of time (12 hours).


That is not grout in that section.

That is either caulk with grout layered on top of it


Caulk that looks like grout.

Grout does not curl when it is installed incorrectly, it cracks and breaks off in chunks.

You can caulk over grout at tub top but cannot grout over caulk (and caulk that looks like grout is usually crap).

Since the gaps are on the larger side - not obscene but larger - I would try to grout the area... see if it lasts without cracking and then silicone over it if you notice it cracking.

If you try to apply silicone you will need to go deep into cracks (1/4-1/2"), get an edge, let it dry and do another round or two of caulking. You cannot do all of that silicone at once or when it cures and you have a failure piece, the whole system will come out in chunks of silicone.

enter image description here

So here it is - The yellow highlight... that's grout. The red circle is an example of an area (not the only area) that is not grout. The webbing at the top of the "grout" shows it is not grout as grout doesn't do that, ever. You see how dry the yellow area is, that is what grout looks like. Grout cracks in large lines/chunks.

Also if there is caulk on grout - what some are suggesting and maybe...

  1. Wow when you grout you fill the damn gap if this is the case I am not even sure if they filled half the gap.
  2. The caulk wasn't silicone (should be) - silicone doesn't dry or peel like that. Sure looks like caulk that looks like grout.
  • My interpretation is that the caulk is peeling away, taking bits of grout with it. – FreeMan Feb 1 at 16:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.