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Unread 06-17-2022, 03:48 PM   #1
Fractal20
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Questions On Tiling a Bathroom Floor

Hi all, two months ago I got a lot of help on this forum for tiling a tub surround on this thread: https://www.johnbridge.com/vbulletin...d.php?t=132187. I'm now getting ready to tile the floor. I'm assuming since it is a separate project at this point that it makes sense to start a new thread?

I've been doing a little research about tiling the floor and I have a few questions that I would love to get advice on

(1) It appears that the subflooring was redone on the bathroom sometime in the past 20 years I would guess. It consists of 3/4 plywood that just has a thin vinyl flooring on top currently. My plan is to go the 1/4 inch cement board route rather that Ditra. Do I need to remove the vinyl before laying down the cement board, or is it okay to put the cement board on top of the vinyl flooring?

(2) The floor joist situation is a little odd. The original floor joists under the bathroom are actually 2 inches in width (not 1.5), but when the bathroom substrate was redone, it looks like in, what I assume was an effort to make the floor more level, that a lot of the floor joists have a 2x6 or 2x8 (modern so actually 1.5 in width) sistered on to them and this is what the plywood is actually resting on. The joists span ~10ft under the bathroom between the supports. I ran the deflector calculations on the website here and it said it would be okay for ceramic tile. But I wanted to double check that the extensive sistering isn't necessarily a concern.

(3) Nothing in this house is actually level. The bathroom is in an L shape and is pretty small, ~50 square feet. I only have a 4ft level. Along the narrow width of the L it seems like the floor is about an 1/8th of an inch off. Along the long part of the L, the first half is about an 1/8th of an inch off as well, but the second half seems to be level. Do you think it is okay to get by not doing any self-leveling compound? If it makes a difference, I'm planning on using tile that are 12in x 12 in

(4) Since the current bathroom floor is just the thin vinyl, I'm imagining that the toilet flange will be low after the tile is installed. I assume this is a common problem. Would the best approach be some kind of adapter like Set-Rite system?

Thanks for your time, I appreciate it!
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Unread 06-17-2022, 11:29 PM   #2
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1) Have you checked for a relatively thin layer of ply or lauan under the vinyl? I ask because it’s relatively uncommon to run vinyl directly to the 3/4” subfloor.

2) The sistering is actually strengthening the floor, not detracting from it. Did you run the Deflecto numbers using just the original 2” wide joists?

3) You might need to do some prep work here. With your relatively short level, it’s harder to see the overall picture. The standard for flatness for your substrate, when used with non-large-format tiles (tiles with all facial dimensions under 15”) is 1/4" in 10' and no more than 1/16" in any given 12".

4) Raising or extending the closet flange to the height of the new floor or to approximately 1/4” higher than the finished floor is ideal. Doing so prevents the use of excessively thick wax rings.

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Unread 06-19-2022, 07:35 AM   #3
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Bubba has you covered so I'll just add a bit...

You will want to remove the vinyl because you cannot determine if the vinyl is sufficiently adhered to whatever is under it. The 1/4" cement board needs to be installed with thinset mortar under it. If you're lucky, and as pointed out, there might be 1/4" lauan under the vinyl so you can just pull up the whole mess.

Check that those sisters are properly fastened to the original joists.
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Unread 06-21-2022, 08:28 AM   #4
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Thank you for the advice! I'll have to double check about the possibility of 1/4 lauan. A few more things

1) From what you wrote it made it sound like that if there is a 1/4 lauan, that it is easier to remove it with the vinyl, then just the vinyl. Is that what you were implying?

2) If there is a 1/4 lauan layer, then I would guess that the plywood subfloor is actually just 1/2 inch. My memory is 1/2 inch isn't thick enough. If that were the case, would you suggest trying to remove just the vinyl floor to save the addition 1/4 lauan layer? Or put down a separate 1/4 layer of plywood? Or would a 1/2 layer of cement board rather than a 1/4 layer make up the difference?

3) I'm trying to get a sense of the timeline with dry times. So cement board is put down with thinset and then needs to wait 24 hours. Then the tile is put down and also needs 24 hours before the sealant can be applied? Then 24 more hours with the sealent? So ~3 days of total drying time?
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Unread 06-21-2022, 08:40 AM   #5
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1. That is sometimes the case.

2. No. If your subfloor is actually only 1/2" thick, your best option would be to remove the entire floor/subfloor and start over with nominal 3/4" plywood or OSB.

3. There is no wait time after installing the CBU. You can tile immediately. The 24 hour wait tile after setting the tile would apply before grouting. Not sure where you'll be using sealant, but you would need to wait 'till your grout cured sufficiently, and 24 hours would be a reasonable time for that.

My opinion; worth price charged.
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Unread 06-21-2022, 10:53 AM   #6
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I just drilled out a plug to verify about the lauan. It doesn't seem to have multiple layers and was just a pure 3/4 inch plug. So I'm pretty sure there is no lauan, unless it was glued really well to the plywood.

Just to verify, I should definitely remove the vinyl? Somebody mentioned removing it because you don't know how well it is adhered to the subfloor. If when I try to remove it, and I find that it is really hard to rip off, does that mean it is safely enough adhered to just leave it?
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Unread 06-22-2022, 01:10 PM   #7
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I'm trying to decide on tile and found some slate tile that was leftover from a job at my local tile store. I just wanted to double check the output from the deflectolator. It yielded a rating of L/426 which said was okay for ceramic (and I presume porcelain?) but not natural stone. This slate tile is small, 2x4 inches, matted together into square foot squares. I just wanted to double check if there is any wiggle room with the rough deflection if the tile is small like this.
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Unread 06-22-2022, 04:21 PM   #8
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Porcelain tile is ceramic tile, Bob.

With tiles that size, you're basically ending up with a coat of grout with some small pieces of tile pressed in and I would expect the strength to be no better than soft natural stone tiles.

Straight answer to your question is, no, there is no wiggle room in the industry standard requirements for subfloor deflection based upon using smaller tiles. Indeed, the industry sometimes limits the minimum size of ceramic tiles for some subfloor/substrate combinations.

And there is at least one tile installation product manufacturer who will warranty a stone installation over subfloor deflection no grater than L/480, rather than the industry requirement of L/720, if you use their setting products.

But it's all a matter of risk tolerance. You wanna give it a try with what you've got, it's entirely up to you.

My opinion; worth price charged.
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Unread 06-22-2022, 06:03 PM   #9
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Thanks for the info CX. You said that there is no need to wait for the thinset under the cement board to set before tiling. I just wanted to double check if that is still the case if it is going to be walked on. For example, if I do the thinset and cement board over the entire floor and then go to the back of the bathroom and start tiling towards the front I'd be walking on the cement board and thinset. Is there any issue walking on it in that case?

Also, just to double check, the seams should be taped and mudded on the cement board as well right? So if you are walking on the cement board as it is setting I assume you just are careful to avoid stepping on seems with the fresh thinset?
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Unread 06-22-2022, 06:19 PM   #10
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Feel free to contact the manufacturer of the CBU, Bob, if you're skeptical about getting questionable advice from some guy you've never met that you found on an Internet site. I would be.

Many people who set tile over CBU floors fill and tape the joints as they set the tiles to prevent making "speed bumps" of cured mortar and tape. You might wanna try that. But yes, if you fill and tape beforehand, you'd obviously want to avoid walking on your freshly treated joints.

My opinion; worth price charged.
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Unread 06-23-2022, 09:45 AM   #11
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If the vinyl is stuck down good and it's truly stuck to the subfloor then you can go right over it with cement board.

Since you would be thinsetting underneath the cement board and then fastening it down there's no reason that you couldn't walk on it immediately.

Personally, I prefer to thinset and mesh tape my seams ahead of time so that if/when you have to pull a tile up you're not pulling the mesh tape up as well and making a big mess.

But it' doesn't take no 24 hours for that stuff to dry. It'll be dry enough to start tiling over in a couple of hours and if you're really trying to move you could use rapid setting thinset for your seams.
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