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Unread 07-17-2019, 09:09 AM   #1
jeffmattero76
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Lauan and tile

It was suggested by KG that I ask this question here.

My son bought a 180 year old house that we are rehabbing for him and his family. Being so old, nothing is plumb and nothing is level.

He wants a tile floor in his kitchen. There were areas where we had to remove the old flooring down to the joists. When we reinstalled new plywood, the floor heights didn't quite match. Therefore, we packed up the lower areas using Luan plywood. One of the tilesetters informed us that Luan is not suitable under hardi backer. As it turns out, from other forums here and other reading, I now understand that he was correct. Due to the amount of staples used to lay it down, the Luan would be a real problem to remove.

Thus, I am looking for options. I thought about painting the floor with redguard. I know that is approved for use with thinset and tile. As I understand it, the main problem with Luan is that it will likely delaminate due to the water in the thinset. Would a coat of redguard solve this?

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Unread 07-17-2019, 10:15 AM   #2
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Jeff, I'll post a link here to your thread on this project so folks can see what you're doing and what's been previously asked and answered and we need not duplicate all the Q&A here.

Personally, I think you got good advice on your project thread and if you want to tile over what you have anyway, that's certainly your prerogative. We can't guarantee failure any more than we can guarantee success, we can only tell you what the ceramic tile industry says and where the smart money is betting. Your house, your tile, your choice.
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Unread 07-17-2019, 11:13 AM   #3
jeffmattero76
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Thanks. I know it is not industry standard, but we are where we are. I am simply looking for opinions on the best way to move forward from those who have experience. I would guess that I am not the first person who put luan down to pack up an uneven floor.

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Unread 07-17-2019, 11:23 AM   #4
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Hey Jeff - as I posted in your other thread, ply over the luan would be good solution; you would still need CBU or Ditra before tile so you’re looking at a 5/8” overall increase in floor height. Is that too much for your project?
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Unread 07-17-2019, 12:07 PM   #5
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Thanks, but yes, that would not work.

As I see it now our (both less than desirable) choices are to cover the entire floor with 3/8" plywood, and tile on that (no cement board), or paint it with a couple coats of Redguard, then cement board and tile. I am just trying to figure out which of those two options would be better.

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Unread 07-17-2019, 12:25 PM   #6
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Hmmm, I see your point. In that case, I would go with CBU over the existing floor. You’re going with 1/4” I’m guessing to minimize height difference?

No redgard, don’t see it gets you anything since the CBU is screwed down to the joists over a bed of thinset to fill any voids between the layers.
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Unread 07-17-2019, 12:27 PM   #7
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Jeff, while there is an industry accepted method of tiling directly to a plywood substrate, there are very specific requirements for doing so. Your situation does not qualify under those conditions and even if it did the absolute minimum thickness you could use for your top layer of plywood is nominal 1/2-inch.
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Unread 07-17-2019, 01:07 PM   #8
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Ok, thanks to all of you for your insight and advice.

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Unread 07-22-2019, 04:58 PM   #9
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I think if you do go CBU over your luan patch work, the biggest thing you also need to remember is thinset it down. A LOT of people don't, so if you took that step even with your questionable subfloor setup, I think you'd likely be ahead of the game compared to probably 90+% of installs around. Especially if you use a strong A118.15 mortar under it. I would recommend Mapei Ultraflex RS (the Mapei Rapid Setting tile mortar at Lowes is the same thing...) it's ridiculously strong mortar, you'd also get the possible benefit of doing it, and getting everything set 100% before walking on it, so less chance of voids and a better chance of a good bond to the floor.

For the Redgard and waterproofing. Well, in the two bathrooms I saw in your other thread, no issues, and presumably water would get on them from people getting out of the tub and the like. In the kitchen where the tiles did crack, the water damage was extensive, and there was rot on the actual plywood subfloor as well once I saw how everything looked demolished. My concern with waterproofing under the floor is that the liquid membranes don't really stick to wood that well. They'd probably stick with a coat of an oil primer, but imo they just don't stick that well to wood. Then of course when you screw down your CBU you're puncturing it anyway. They do stick well to cement. I think it would be better to just waterproof the top CBU once it's all done, and make sure the CBU joints are taped and thinsetted too. In theory the liquid membrane is a crack isolation membrane for the tile, so it might buy you some more insurance, too.

I think modern A118.15 mortars are amazing, and I think do allow you to "get away" with a lot more. So definitely go spend the money for a decent mortar like that. Make sure as well you/the installer gets good coverage on the tiles as well, if you've not seen the "trowel and error" video https://www.youtube.com/watch?v=Way5bMh-eYg You definitely should watch it.

One thing I was told by a pro installer at a TCNA conference (I kind of just happened into, free food and beer, yay...) was "It's usually not the first thing you do wrong that gets you, it's the second, third, or fourth thing." So in this instance, make sure you do everything else you can right.
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Unread 07-22-2019, 09:21 PM   #10
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Great, thanks for the info#

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Unread 07-22-2019, 10:17 PM   #11
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Joe, you seem like someone who wants to grow in this trades, so I'll mention a few things for you to consider:
Quote:
Originally Posted by mrberryman
...a better chance of a good bond to the floor.
What you need to realize here is that the bond between the subfloor and the cement board shear within a couple of years. It's not permanent. Using a high dollar mortars will keep it bonded for a few more years. But it'll still shear. And while a lamination that strengthens and stiffens the floor is a benefit...it's only temporary until the shear. I'd guesstimate that less than 5% of installers know this bit.

Quote:
Originally Posted by mrberryman
... My concern with waterproofing under the floor is that the liquid membranes don't really stick to wood that well. They'd probably stick with a coat of an oil primer, but imo they just don't stick that well to wood.
I find the opposite true. It's always been true of Hydroban. And it's been true with RedGard after it was reformulated about 10 years ago. Although I've never tried it on solid dimensional wood...or cheap lauan. But in this particular case, it wouldn't matter how little it did bond because its purpose is only to form a barrier to keep the moisture in the mortar from the lauan while it's drying.

Quote:
Originally Posted by mrberryman
...Then of course when you screw down your CBU you're puncturing it anyway.
That doesn't matter in the context of keeping the lauan dry. This is a one-time shot of moisture and only trace amounts of moisture will get around the fasteners as it dries.

Quote:
Originally Posted by mrberryman
One thing I was told by a pro installer at a TCNA conference (I kind of just happened into, free food and beer, yay...) was "It's usually not the first thing you do wrong that gets you, it's the second, third, or fourth thing." So in this instance, make sure you do everything else you can right.
Unless, perhaps, the first thing you do is build your install upon a weak foundation of lauan.

Food for thought.

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