Kerdi Void [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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06-16-2019, 11:46 AM
First time installing anything involving tile so I’m learning as I go. Chose to use a Schluter shower kit because I could use drywall instead of hardi backer. I did learn after the fact that drywall shouldn’t be taped for kerdi. Remedy for that was using a latex primer over the mud.

I installed my first sheet and it went well with no bubbles. My 2nd sheet went on and took awhile to smooth out but this morning I went to check on it and it had large void where it didn’t adhere good. After thinking about it I had a drywall seam there.

Also around my diverter valve it has a loose edge around the bottom I need to address.

I used the kerdi trowel and ditra set thinset. I will be using 4x8 subway tile. What is the best method you guys would recommend to correct this issue? I’m ocd about worrying if I’m installing things correctly and this is bothering me.

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06-16-2019, 03:32 PM
Zack...Slit the three bubbles you have and force a bit of thinset in there. Now, cut patches that overlap by at least two inches and smooth some thinset behind them and use a taping knife to flatten them out...good to go.

John Bridge
06-17-2019, 04:39 PM
Hi Zack, :)

Looks to me like you are installing sheets that might be a bit big for your experience level. You can install half pieces and overlap them two inches. That will give you a lot more time to smooth things out. :)

06-17-2019, 04:50 PM
The tile you're using is fairly small. That means your Kerdi really needs to be adhered well for shear strength. When I did Kerdi for the first time, I thought I had mostly embedded it well. It turned out I was wrong. I pulled it off the wall and had lots of "tiger striping" with coverage of maybe 60%. That wasn't enough, obviously. When you let your hands glide across the Kerdi, you will "hear" the unbonded sections. They make a hollow sound. If it's just a few bubbles, then no problem. Slit, fill and overlap with Kerdiband (as has been said). If it's more, carefully evaluate!

06-17-2019, 05:11 PM
If it was a rather large area that didn't bond, I might try to cut and fill it. But those three bubbles to the left of the valve seem fairly narrow. I'd cut a rectangle around all three of them, remove the piece, and patch over it.

06-17-2019, 06:46 PM
Ate they hollow air bubbles or thinset bulges?
It almost looks like you had a kink in your kerdi. What I mean is you didn't start in one corner and work bout from there. If you let the kerdi stick out in front of where your smoothing but it has a wrinkle you may need to pull it up and then smooth out from the corner. I do see the drywall mud line. If they are bubbles cut them out and patch over them. Don't let a buildup of thickness happen or it may effect tile.

06-17-2019, 08:12 PM
Thanks for all the replies.

I ran my hand over all of it and the wall with the niche bonded good. The plumbing wall has those hollow air bubbles. There was also a couple of spots that sounded hollow like it wasn’t embedded good but it wasn’t bubbled out. One is at the bottoms about a 4-5” diameter spot.

I’m halfway tempted to pull the entire sheet off and try again but the pieces that did embed will be a pain to remove.

06-18-2019, 04:27 PM
Cut the piece out to check it out. The fleece that is embedded looks like it’s stuck on good. Tips to get it off?

Also update on running my fingers over it. It feels smooth and solid but some spots if I apply pressure and dig my nails into it I can feel small ridges. The piece isn’t loose so it did embed some but now I’m worried if it is embedded enough? After messing with that fleece I’d hate to rip that entire sheet off.

06-18-2019, 04:52 PM
It's a judgment call on your part. Hard to say from my chair here (or anyone's for that matter). All I know is that my first Kerdi application was a complete disaster and warranted a redo (wasting about $100 worth of Kerdi). I had picked Hardiebackers which sucked all the moisture out of my thinset. So much for learning. :mad:

You really want the full contact without ridges below. Will it work out with less contact? Probably yes, but I wouldn't take the risk. If in doubt, careful and frequent peel-back will make sure you get the contact you need. I also resorted to backbuttering the Kerdi in places that were revealed void upon peeling back. That way I got close to 100% contact. I'd say you would want at least 90% contact. Also, using grey thinset will help as it gives you a visual indication whether the Kerdi is embedded. It will temporarily turn the Kerdi a dark grayish orange.

In my view, there is a learning curve to Kerdi that is not apparent when one watches the Schluter installation videos.

06-18-2019, 05:16 PM
i say if it.feels solid leave it ... just patch the bubbles. dont worry about micro wrinkles but I usually dont get wrinkles.

06-18-2019, 06:19 PM
Paranoia got the best of me and I took the entire lower section off. Disregard next to the valve where I was scraping thinset off.

They do make it look easy on the kerdi videos.

06-18-2019, 08:32 PM
Zach, looking at all those voids and dips, you probably did the right thing. Just skim-coat a thin layer of thinset on top to make it even. If you have to grind down the existing thinset, that might be yuckier. Let set up and then do your Kerdi membrane again. This time, make sure you peel back enough to check for coverage. I peeled back the entire sheet in smaller portions to make sure I had contact. Once your bonding fleece is thoroughly penetrated with mortar, bonding and re-embedding will be easy. Do burn a thin layer of thinset into sections of your Kerdi back (with the flat side of the trowel) should you discover areas without sufficient coverage.

06-18-2019, 09:55 PM
The magic is proper prep of the wall (flat and plumb helps a lot), then ensuring that you moisten down the wall prior to applying the thinset letting all of the moisture in the mortar stay there without getting sucked out, drying it, and last, but just as important, having the right consistency of the mortar. Using a quality one means it will also be smoother, making it easier to embed the material. If all of those are done properly, it is easy to install. The mortar needs to be fluid enough to flow around the fleece fibers and let you flatten out the ridges from the notched trowel when you try to embed it. If you pull a section back, it should have full coverage, and then go back on with almost no effort since there's thinset on both surfaces (the wall and the back of the membrane).

As John mentioned, until you get good at it, don't try to use large will take you too long to spread out the thinset, probably allowing it to dry out some prior to getting the sheet up and embedded.

06-19-2019, 06:11 AM
Watch some kerdi videos,, they show really liquid thinset and wet that wall real good until it stays wet looking for 10 mins then wet it again and proceed. that wall looks very rough now. work on smoothing it our best you can.
It does look like your thinset got to dry.
It looks best you pulled it up

How hard was it to pull off? .

06-19-2019, 03:15 PM
It wasn’t bad to pull off but the fleece did come off certain areas that it was adhered. The fleece that’s left is challenging to remove.

07-09-2019, 08:06 PM
Just an update. I tore the bad spot out and redid that section. Got my base set and everything complete. Did a water test and no level change other than minor evaporation. No wicking that I can see with my untrained eye.

Thanks to everyone for the help. Have to kerdi Fix the outside corners where they popped up a bit but other than that I should be ready to tile.

On another note does everyone trust the kerdi niche overlap or do you seal that seam better?