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Discussion Starter · #1 ·
First time tiling and messed up the bottom row and created a big lip between bottom row and next row up along back wall of bathtub. Decided to remove the bottom row and fix it. After removing the tiles, I was using a scraper along with chisel/hammer to remove the remaining thinset on the wall. The vibration kept knocking tiles loose a couple rows above. These tiles were laid about 72 hours ago, but after they fell off, the backs were mostly clean and the thinset looked damp.

1) I'm fighting a losing battle. The more I scrape the old thinset back to the redgard, the more tiles come loose, and require more scraping. I've tried cold chisel/hammer, just scraping with a stiff putty knife, and carbide grout blade on multitool, but all cause tiles to come loose. At this point, I'm considering removing all tiles, cutting the membrane and peeling it off, then re-redgard the area to start over. Ideas?

2) What am I doing wrong here to prevent it happening second time around? Does it simply take more than 72 hours to bond to the tiles, which is why the hammer vibration is causing tiles to cleanly pop off?


 

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The good news is that you’ve discovered the problem before you got very far, hopefully.

After setting your first tile you should remove it and check the back of the tile to evaluate coverage and bonding. It should be mostly covered in thinset. You can see in your first photo that the coverage on this tile is so sparse that I’m surprised it held in place at all. The video linked below shows what the underside of the tile should look like when you pull it up.

Why this happened could be due to a number of different things. Since this is your first tile job it could be that there was too much time between when the thinset was trowelled on the wall before the tile was embedded in it.

If there was a problem with the thinset mix that weakened it, you would still see thinset adhered to the back of the tile, but it does seem odd to me that you’ve been able to scrape of the thinset without damaging the waterproofing membrane underneath. Presumably you’ve reviewed the thinset mixing instructions to ensure that you followed them, including the slaking time. 24 hours after setting thinset is still soft enough to cut with a knife. I clean up any excess thinset between the tiles that would block grouting using a knife the next day (that wouldn't be a good idea where there is a waterproofing membrane, of course). By 72 hours it should be very hard.

The real tilesetters on the forum might have different opinions on this.

Chris

 

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Discussion Starter · #5 ·
Thanks guys. I think huesmann is right....I believe my thinset mix was too dry.

The wall tiles above the niche were from the 2nd day/2nd batch of thinset and it was definitely a wetter mix. These tiles are stuck on extremely good, unlike below the shower niche that pretty much just popped off. The thinset bag says "mix to pastelike consistency", but I guess I did too dry of a paste. Going online though they actually have the water-to-thinset ratio in the instructions, so I might mix one batch by measuring to see how it's supposed to be.

That's a good idea to pull a tile off and check for coverage. It's something I knew should be done, but was so focused on trying to get everything lined up first time around and just didn't do it :/

Ended up just cutting out the section of cement board on the bottom - as you said, the membrane was getting beat up pretty bad and it was taking forever to grind it down with a grout multitool blade.

Now the only issue is figuring out the best way to tile top down. VersaBond thinset says 4 hour pot life and 20 min set time. Thinking to do one row starting from top, tape each tile to something above that's dried and make sure they stay tight until they're set enough to stay put and continue on. So 20-25 min a row isn't too bad........:plain:

 

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Discussion Starter · #8 ·
Thanks all, it was definitely too dry of a mix. Weighed and measured out correct ratios second time around and it's a much wetter mix than eyeball from what it looked like in youtube videos. Additionally did a tight backbutter on the 4x16 subway tiles using flat side of trowel. Probably not necessary for these lightweight tiles, but definitely doesn't hurt to fill in the recessed areas on back of tile. Pulled off first tile after sticking on and it's fully covered with thinset this time.

I do have to say working top down was close to causing a brain aneurysm though. Tiles kept sliding down and even with tape slightly slipped down so that the built in spacers were tight against each other. Had to stop for 15 min every 2 rows and consistently push tiles back up and add extra tape to hold them tight until they set enough.
 

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Well, yes and no. If his "paste" is too dry he may still be getting good contact, but not good adhesion.

Welllllll, OK, maybe splitting hairs with word choice, but 95% sure that thinset was either too dry to begin with, or it skinned over and not much pressure was used to press the tile down (which would probably have mitigated the skinning problem somewhat). For DIYers that move more slowly than pros, what I would recommend is back troweling each tile and installing that way. (This is NOT back buttering). In other words, apply the thinset (of proper consistency) to each tile, rather than a large section of wall all at once. That way there can't be any skinning.
 

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Discussion Starter · #11 ·
Welllllll, OK, maybe splitting hairs with word choice, but 95% sure that thinset was either too dry to begin with, or it skinned over and not much pressure was used to press the tile down (which would probably have mitigated the skinning problem somewhat). For DIYers that move more slowly than pros, what I would recommend is back troweling each tile and installing that way. (This is NOT back buttering). In other words, apply the thinset (of proper consistency) to each tile, rather than a large section of wall all at once. That way there can't be any skinning.
I like this idea and will try it out. Have most of the tiles precut, but I'm slow regardless. And then if I have to make a cut, it's game over. Basically have been only troweling an area on the wall for 1-2 tiles to prevent skimming, but at this point, might as well just back trowel the tiles as I go to keep it cleaner and 100% prevent skimming.
 
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