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Unread 01-25-2022, 10:35 AM   #1
gregm93
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Water behind tile causing efflorescence in Shower pan

Hi all,

We recently completed a shower install using a Kerdi pan with go board on the walls (mixed install due to supplier constraints). Install went well but after a weeks of use their is some efflorescence coming through the grout lines of the floor. Upon cleaning I punctured our silicone joint where the floor meets the wall and water started coming out. We then scraped out this silicone joint on all four walls. On each one we had significant water seepage come out once the silicone was removed.

My theory, and I don't feel very confident here: the water is penetrating the grout lines on the wall tile and running down behind the tile on top of our go board. When it reaches the bottom it can't push out through the silicone so it sits there until it can weep through the floor grout lines slowly, dissolving salt from the mortar and causing efflorescence in the process.

In the specific spots where the efflorescence is occuring it is taking a long time to dry out after use.

Notes:
Tile is 12x24 glossy porcelain (not permeable)
Grout lines are 1/16th
All grout is Mapei FA
All grout was sealed as well
Inspection of walls for holes in grout/silicone checked out

This one has me stumped ????


Located in cold Buffalo New york
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Unread 01-25-2022, 10:42 AM   #2
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Unread 01-25-2022, 01:02 PM   #3
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Welcome, Greg.

If you don't add that geographic location to your User Profile the information will be lost before we leave this page. And it's frequently helpful.

Were the wall tiles install with the required minimum of 95 percent thinset mortar coverage on the back of each tile? Or were the tiles "spot bonded" to aid in making them lie flush on the wall?

The problem with the water running out the bottom joint is, in my experience, the result of voids in the wall bonding mortar, allowing the accumulation of moisture, which finally gravity feeds to the bottom of the walls. The flexible sealant there (a proper installation according to tile industry standards), in combination with the surface applied waterproofing membrane, allows for this moisture to build up rather significantly, and surprisingly, at the bottom of the wall.

As to the efflorescence, if that's what you have, we'd need to know about the bonding mortar and grout used on the floor and wall.

My opinion; worth price charged.
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Unread 01-26-2022, 12:21 AM   #4
Tool Guy - Kg
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My initial question is the same as CX’s: did you achieve at least the minimum 95% mortar coverage behind the tiles?

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Unread 01-26-2022, 02:31 PM   #5
gregm93
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Yes we did! 1/2" trowel on the walls and back buttered every tile.
Does it seem reasonable that if this much water can penetrate the grout lines, then the water could also drain if the bottom joint was grout as opposed to silicone?
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Unread 01-26-2022, 03:41 PM   #6
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The bigger the tile, the harder it is to fully embed it by squashing the notches flat and filling in the gaps in between. So, while burning in a layer on the back of the tile certainly helps for the bonding, with a notch that large, you probably have some significant voids underneath the tiles.

In one class I took, they had us install some clear glass tile where we could see how well the notches were collapsed. It took a LOT of hard pressing and back and forth to get them all flattened out.

I'm a fan of slant-notched trowels. The trowel notches are taller than 'normal', and because they aren't vertical, after the trowel passes, they literally fall over on themselves making a nearly flat surface that has the proper amount of thinset gauged onto it.

A 12x24" tile is 288sq in. Say you weigh 144, and could put all of your weight on the tile, that's 1/2# per square in...almost nothing. To get those notches flattened, because you can't just push it down (or in this case, against the wall), you have to move it back and forth 3-4 times, or maybe even more, depending on how far you can move it...the suction from the tinset makes that REALLY hard work, and you almost certainly won't. In another class, when setting large format tile, they demonstrated using a random orbital palm sander with no sandpaper on it and used that to vibrate the tile to embed it well. IOW, as opposed to say a small 2x2 or 4x4 tile where you could apply lots of pressure and flatten the ridges, without working at it, you will NOT flatten them easily on a 12x24" tile, and almost certainly have some gaps behind it.
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Unread 01-26-2022, 04:23 PM   #7
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Yes, under those circumstances, water could/would drain out of the bottom grouted joint, Greg. Potentially for weeks with the shower not in use. Yes, I've seen that trick.

My opinion; worth price charged.
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Unread 01-28-2022, 02:52 AM   #8
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Water Behind The Tile

This thread I find interesting because I have often wondered about this situation happening. From what I've read on this forum as well as other places, water WILL get through the grout joints, and possibly even the tile in some cases, to the back side of the tile. Then, as CX says, gravity will carry the water down to the bottom of the wall. Now, with the change-of-plane joint between floor and wall "sealed" with like 100% silicone, or possibly polyurethane type sealant, it seems like that water will be held "captive" in essence between the tile and the waterproof (or 'resistant') membrane on the tile backer? Would this be a correct assessment of what will happen?

If this is the case, would there be some way to incorporate "weep holes" leading from behind the tile out to the shower floor? I could see these being immediately above the change-of-plane sealant, which would seem to be the lowest point the moisture could drain to. The sealant would prohibit the water from going lower, and the joint grout allows the water to seep through very slowly, so essentially it is 'trapped' behind and will only come out over an extended period of time.

Another point that was brought up was possibly lack of complete mortar coverage, voids in essence, between the back side of the tile and the tile backer. Spot bonding would no doubt leave a few voids, air spaces, I guess, where moisture would gravitate to. Why, I don't know other than the fact that water will generally flow in the direction of the path of least resistance;it there is a "dry" area laterally, to the side, versus a 'saturated' area below, then it will flow laterally to the dry area. It hadn't really occurred to me that spot bonding, I suppose for purposes of dealing with lippage, will in all likelihood increase the incidence of water behind the tile.

Would there be an appreciable difference in the amount of water passing through grout joints depending upon whether they are done with sanded grout versus unsanded grout? Would a 'fortified' (latex modified) grout, or an epoxy type grout lessen the chance of water passing through? Wish you success in dealing with your situation Greg.
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Unread 01-28-2022, 04:18 PM   #9
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Epoxy and acrylic grouts tend to be less porous than cement-based ones.

On a conventional shower construction, the pan rapidly gets damp and will stay that way unless the shower is only used very rarely. On a surface applied membrane, you don't get as much wicking, as the water wants to go where it's drier and thinset is denser than deck mud. If you have full coverage, with a surface applied membrane, it tends to dry out in between uses.

TO help on any shower, wipe the surface down when the last person is done for the day. That also helps keep any soap scum from accumulating and mineral deposits from hard water spots occuring. Many people don't use, or don't let a fan run long enough during and after using a shower. A timer can help, or, you can buy fans with built-in moisture sensors that will continue to run until it senses the moisture level is lower. Panasonic fans have that as an option, and you can buy a wall switch with that built in. The wall switch isn't as efficient, as the 'steam' needs to build up down to the switch, rather than at the ceiling if it's built into the fan, so it turns on sooner. About 30-minutes after finishing a shower is about what it takes, but that also assumes you have good air exchange (can't leave the door closed fully).
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Unread 03-18-2022, 07:21 AM   #10
gregm93
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Thanks everyone for the extremely informative replies. I've seen the palm sander trick before and think I will be incorporating that in the future.
Ideally with any install we have full coverage behind the tile so water intrusion is at a bare minimum. However, this talk of water draining at the change of plane in the floor has me wondering if I should grout that joint on all future projects. I'd love to hear some more opinions on that.

The apparent downside in my opinion is that there is a strong likelihood that the grout will crack and fall out over time
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Unread 03-18-2022, 11:13 AM   #11
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I can't account for the water problem, but I know something about cracking and it's causes. I grout everything in every shower I build and tile, and I've d.one hundreds of them in my time.

Showers need to be framed tight. I use screws instead of nails. The corners of the shower need particular attention. The framing members there must be drawn tightly together.

I have to admit, though, that I've not done backer board showers. They've all been either mud jobs or waterproof membrane.
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