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Unread 05-27-2022, 11:52 AM   #1
C. Daniel
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Best way forward for crumbling grout?

Hi all, I've read these forums a few times and found them really helpful. This is my first time posting.

My wife and I recently hired a contractor to install a new bathroom, including shower tile. All the shower tile is installed over kerdi (the orange stuff). We noticed that less than six months after completion, the grout is crumbling between the floor tiles. The grout also seems to discolor pretty quickly (within a couple of weeks), though it can be easily scrubbed away.

From what I've read, crumbling grout is usually a result of poorly mixed grout or an "unstable" subfloor. The grout is only crumbling in part of the shower floor; not the rest of the shower floor, nor the tile floor in the rest of the bathroom, outside the shower.

I suspect (though am far from certain) the problem is poorly mixed grout, for a couple of reasons. First, building inspections in our area are pretty strict, so I'd think the inspector would have said something if the joists were too small, spaced too far apart, etc. Also, it turns out our contractor did questionable work in other areas, so I wouldn't be surprised if he didn't mix the grout thoroughly enough, or used the wrong ratio of grout:water.

My main question is: what would you recommend in terms of best next steps? Try to dig out the grout and re-grout? Tile over the existing tile? Something else?

Also, I'm somewhat concerned about water getting underneath the grout. I know grout isn't completely watertight; should I be concerned about water getting behind anything? I've heard kerdi is pretty great stuff, but given the quality of other work, I can't be confident that he did the kerdi properly.

We'll do what we have to do in order to fix it correctly, but I'd like to pick the lowest hanging fruit first. I don't want to rip everything out if there's a simpler solution that is likely to be effective.

Two photos attached; I'm happy to take others that may be helpful.

Thanks so much for your time!
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Unread 05-27-2022, 02:22 PM   #2
jadnashua
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Is all of the crumbling grout near the drain?

What is the pan made of: foam pan, or deck mud?

Any idea how big the hole around the drain in the floor was?
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Unread 05-27-2022, 06:26 PM   #3
Davy
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Same questions as Jim. Cracking grout usually means there's movement.

Just to confirm, this is over a wood sub-floor and not slab? Any pictures from the construction would be handy.
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Unread 06-08-2022, 06:39 PM   #4
C. Daniel
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Thanks so much for your responses. Here are the answers to your questions:

Is all of the crumbling grout near the drain?
Yes, it's all by the drain. I've attached another photo, which shows where the crumbling grout is (the darker areas right beside the drain).

What is the pan made of: foam pan, or deck mud?
I can't say for sure, but I'm pretty sure it was a foam pan cut to size.

Any idea how big the hole around the drain in the floor was?
That's a good question, I'm not sure.

Just to confirm, this is over a wood sub-floor and not slab? Any pictures from the construction would be handy.
Yes, it's over a wood sub-floor. In fact, it's on the second floor of our home. I'm not opposed to cutting out the ceiling below it, although I'm not eager to do that recreationally...

Some other solutions I've read/thought about:
1. Scuff the existing tile with an angle grinder and lay a new layer of tile over top of the existing tile. But if there's movement, I suppose I'd just end up with the same problem.
2. Try to grind out all the existing grout and re-grout. Same possible problem as before.
3. Grind out the existing grout and find a caulk instead of grout? Is there a caulk that would withstand the movement?
4. Tear out ceiling below and sister joists/beef up framing. Then try one of the solutions above.
5. Rip it out and start from scratch. Least idea, probably most thorough.

Since this is part of a much larger reno project, the timeline is a factor for us. If I don't make this the top priority, how much do I risk water damage or other longer term damage? The tile is on mortar, which is on top of kerdi. Without you being able to see each layer that's underneath, do you have any hunches about how waterproof it still might be? In other words, I'm wondering if this is a high priority (risk of water damage) or just an inconvenience, and could wait a few months...

Thanks again for all y'all's time.
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Unread 06-08-2022, 08:31 PM   #5
jadnashua
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A Kerdi foam tray can work just fine, but there are a few 'buts' involved. First, the hole in the floor should be about 5" in diameter. The floor should be level AND flat. The thinset under the tray must not have dried out and skinned over prior to setting the tray in place, and you do need to sort of shuffle across it all over to help push it into the thinset.

If all of those things are done, the tray should be fine.

Then, the Kerdi needs to be embedded well into the thinset on top of the tray.

The tile must be well embedded on top of the Kerdi. INdustry standards call for 100% of the edges, and like 95% of the rest of the tile surface be covered with thinset.

If that's still good, there should not be any movement and the grout should not crack.

If someone walked on the thing before the thinset had cured well, it may have broken the bond. Usually 24-hours is okay for a light load, longer for a heavier one. Depending on the grout, you may need to let things cure longer before you apply it, and then, that needs some time to cure.
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Unread 06-09-2022, 04:16 PM   #6
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Chris, the reason the size hole in the plywood is critical is because if the hole is too large, it doesn't support the foam well. Then when someone steps in that area, the foam flexes. We've seen that before here on the forum.

The waterproofing layer is the Kerdi so if the shower is built properly, you can use it before it's grouted and it not leak. I'd say if it's leaking, you'd see it in the ceiling below. But if the drain or floor is flexing and not leaking, it might flex enough to eventually cause it to leak.
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