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Old 12-14-2007, 03:08 PM   #1
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Grout, caulk, and inside shower corners

Question in a nutshell: What is the most correct way of handling grout at a change of plane in a shower, particularly at inside corners?

I've done some searching in the advice forum and in the Liberry, but I have only found bits of an answer, not anything comprehensive in one place. I think I've figured it out, but a number of folks have contradicted my answer, including a few local "pros", so I'm asking people I trust.

What I think the answer is:
  • General rule: Don't grout in corners. Leave them open and caulk instead.
  • Partial exception 1: Outside corners are a lot less sensitive. If you have a stable structure, you might get away with grout here, but it isn't "right".
  • Partial exception 2: If your substrate is a contiguous mud box instead of a board product, it may be stable enough to let you use grout in the corners, but this also isn't "right".

The only part of that I'm certain of: "It's industry practice to caulk at any change of plane". As an amateur, that really doesn't tell me enough.

Background story: I have a glass tile shower that I did myself. I was told that glass has extra susceptibility to flexing, so I should pay extra attention to caulk rules. When I grouted, I used a dental tool to rake the grout completely out of the inside corners. After the grout was well cured, I went back and filled the corners with caulk. I grouted the outside corners along the top of the curb on the reasoning that it's a solid mud curb so the grout shouldn't crack, and if it does it'll be because I have much bigger problems. I haven't seen any problems yet, but it hasn't been finished long enough for me to say there won't be.

I've never really been happy with the color mismatch between the caulk and grout, but I've now seen other jobs that didn't have that problem, so I'm wondering if the caulk color was mislabeled and have investigated replacing the caulk. However, when I started looking for a color match, local "experts" started popping out of the woodwork and telling me I'd done it all wrong. Things I've heard:
"You should have put grout in the corners. You only use caulk at joints with dissimilar materials like where tile meets preformed shower pans."

"Grout in the corners is fine if you just put a thin bead of caulk over it. If it does crack, the caulk prevents mildew from growing in the crack."

"You aren't supposed to grout the corners, but everyone does because it's hard not to, and customers complain if you don't. You might get hairline cracks, but it'll hold up fine."
They've generally said I was a fool for raking out the whole corner. Now I doubt what I thought I knew before. On top of that, I'm now planning for a second bathroom, a much more ambitious project, and would really like to know the right answer before I start.

So, what is the proper way of handling shower corners? I'm hoping for a complete answer from the pros that not only helps me, but that we can point later newbies toward as a reference. If you want to add a description of your techniques to make it easier or when you think the rules don't apply, that's wonderful too.

Two obvious follow-on questions:

If outside corners should be caulked, how do you handle outside corner tiles, the kind that wrap around the entire outside corner at least an inch or two along both walls/planes?

Is the answer the same for dry environments such as a tile floor with a few tiled steps, or is it accepted just to grout and live with the cracks since they won't be wet and growing mold?

Thanks to all for putting up with this.
Eric Sobocinski
DIY Junkie

Last edited by esobocinski; 12-14-2007 at 03:18 PM.
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Old 12-14-2007, 04:30 PM   #2
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I've never yet seen a caulk that dries and matches 100% to the grout, so, I grout everything, except, floor tile to tubs, wall tile to tubs and pre-fab fiberglass pans, backsplashes at countertops, tile to window frames and any wood borders, these get caulk, most other areas are grouted so it looks nicer and matches, I leave behind the matching caulk, so if it ever developes a hairline crack, then they can fill it with the caulk.
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Old 12-14-2007, 10:07 PM   #3
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dont know about over in merca but mapai grout n silicone are a pretty good match.........i always use silicone in the corners
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Old 12-15-2007, 03:35 PM   #4
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I always caulk my corners FIRST to make sure I have caulk in the corner joints to allow for some miniscule movment. I do this since I dont really like caulk on top of grout.
so right as I'm done setting the wall that day I caulk, then the next day grout the walls.
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Old 12-15-2007, 04:33 PM   #5
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I'm with Brian, Caulk the joint before you grout so that you have a soft joint in the change of plain If you caulk first then you will not have to worry about getting grout in the corner. TEC makes good color matching caulks.
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Old 01-08-2008, 09:25 AM   #6
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Grout won't stick to silicone, but silicone sticks to grout
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Old 01-08-2008, 06:36 PM   #7
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we dont grout over the caulked corner.
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Old 01-08-2008, 07:00 PM   #8
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Well there's your answer! (s)

I'm pretty sure the actual TCA guideline is: Every change of plane. Joint must be completely free of anything. You put backer rod in the joint, then caulk over that. I use a backer rod in anything over an 1/8". I saw Musky Mike say anything over a 1/4". His answer should be trusted over mine. That's the complete real guideline from the TCA.

That being said; I alawys caulk inside corners, and at the wall/ shower pan change. Plus that list the other guy said. I've never caulked an outside corner. I also use marble sills on my curbs and not tile. So the only outside corners I deal with are on the jamb which is solid CBU/ 2x4's. Unless your doing a mud wall shower don't worry about those answers. Caulk ( and nothing else like grout) your inside corners. It's up to you if you do the outsides.

You did a good thing by cleaning that joint. Next time though; caulk first.
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Old 01-27-2008, 09:12 PM   #9
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I actually had the same question (I can't post URL link yet the thread id is 57646) my contractor grout & use a clear caulk (I guess I don't have color matching problem) so I guess if there is a crack I'll "see" it

but it's been about 30 days no problem yet!
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Old 01-27-2008, 09:58 PM   #10
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There's really no confusion. As Royce correctly points out, TCA guidelines call out caulk for any change of plane.

Even the pros who do otherwise (based on LOTS of experience ) will tell you it's hard to go wrong following TCA. When the pros don't follow TCA for something like this it's because they've learned what works and what doesn't. The folks who write the TCA specs prolly know that too, but there's no way they could cover all the exceptions and "what ifs." Besides, that's what separates the pros from us Weekend Warriors.

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