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Unread 03-18-2020, 06:18 AM   #16
ss3964spd
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Phew, couldda been bad otherwise..
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Unread 03-19-2020, 08:28 AM   #17
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Ok, that made me laugh. Yep, drywall screws and liquid nails. Well I laughed until I remembered the same guy installed my tub. No way are those screws galvanized. Happily, most of the liquid nails only adhered to the cement board, not the OSB, so I only have a few spots to deal with. Early efforts to remove the few spots haven't been fun.

So, I'm just going to do some sort of transition at the hall, put in another layer of plywood, use floor screws, and go with ditra. Any suggestions about how to do add the extra plywood layer correctly? Also, once it is in, I do want to use self leveler in part of the room. Does anyone have a reccomendation for a product they like?
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Unread 03-19-2020, 12:06 PM   #18
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If your first layer of plywood is at least 5/8" then you can get away with 1/2" plywood for the 2nd layer. You'll want that 2nd layer of ply to be B/C, exterior glue/exposure 1.

First though, take the time to screw the first layer to the joists if it isn't already screwed down. The second layer needs to be installed so that the long edge of the ply is perpendicular to the floor joists, and be sure any 2nd layer seams overlap the seams of the 1st layer by at least 6". Don't fasten the second layer to the joists, fasten it to only the 1st layer.
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Unread 03-21-2020, 11:49 AM   #19
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Thanks for the details Dan, very helpful.

Quandary - my hardwood I meet up to is 3/4 up from the 5/8” OSB. The previous tile was super thin wall tile applied directly to what I’m presuming was 1/2” ply so it was flush. My floor tile is 3/8 and it was above grade with the (now ripped up) floor when that was 1/4” cement with the thinner than thinset liquid nails application.

So, I wish I didn’t have to use a transition but I will ... but, check out the attached photo. The builders ran the board further in than I think is normal? If I start the transition from there it is going to be weird. I’m not quite sure how to remove one board since I can’t run a saw the full length because of the door frame. Ideas?!

One last question. All the good advice and I understand many codes, require 1 1/4 base. I called Schluter to double check their instructions that say I can install straight over 5/8” T&G osb (16” spacing) and they confirmed it is ok. I will be causing some minimal damage to my subfloor as I try to get out the bit of stuck on cement board so it would be nice to have a fresh flat layer. BUT, given my weird door situation and the fact the area I’m working with is small 3’ wide x 9.5’ long (2 joists evenly spaced along the 9’ run) with a 4’ vanity set next to the run, how alarming is the idea of putting self leveler over the area to correct a dip in one corner and smooth the overall surface and put ditra straight over that? Caulking the previous screw holes and the more recent cement board/drywall screw holes would be a chore but ditra and 2 layers of thinset would be pretty close to the 3/8 I have to work with (there won’t be much leveler at the door. Does the 3’ span give me any grace that makes an additional 1/2” layer of ply unnecessary or am I just wishing?
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Unread 03-21-2020, 01:27 PM   #20
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I'm not seeing where we're even sure you have the minimum nominal 5/8ths" OSB there, Robin. Are we sure that's what you've got and that it's got T&G edges and that the joist spacing is no more than 16 inches on center?

Ditra over old, damaged nominal 5/8th" OSB for a ceramic tile floor? You can do it if you like. Keep in mind that when the minimum requirements are being decided for tile substrate products, the testing is done using new material, in near perfect condition, near perfectly installed over joists with zero deflection and the test needs pass only once.

The wood flooring in your photo is stopped at the correct location in the doorway. You generally want the division between floor coverings to occur directly under the closed door, which you appear to have.

My opinion; worth price charged.
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Unread 03-21-2020, 02:25 PM   #21
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I am confident on 5/8 because there is a hole in the adjacent laundry room where I can see the cross section. I’m feeling pretty confident on the tongue & groove because I took a small piece of wire and it only goes down part way on perpendicular seams but is unrestricted on the parallel seams. There is 16” spacing in the basement and the seams/nails in the osb would suggest that was carried through to the second floor. So, I’m not absolutely positive, but plenty to suggest that is what I have.

Great point on like new though. This definitely won’t be no matter how careful I am. Thanks for letting me know that is the correct placement (the laundry room stops one board short of this and apparently that one is the wrong way)! I thought leveling might help but if my issue is deflection I don’t guess it would? Also, even if I was careful with the primer do you think adhesion to the OSB would be a concern?
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Unread 03-21-2020, 02:35 PM   #22
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Some manufacturers of thinset mortar don't recommend their products for bonding to OSB, Robin. I, personally, don't like trying to bond to OSB at all, with any kind of adhesive, but that's a different discussion.

Schluter indicates your subfloor as a minimum requirement (see qualifications in post #20) for use under their Ditra for a ceramic tile installation. If you're comfortable with that, go for it, say I.

My opinion; worth price charged.
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Unread 03-21-2020, 04:22 PM   #23
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I hear you ... and sorry to be reluctantly asking more before I break down and probably just add ply and deal with a transition!!

Theoretically - as opposed to thinset over OSB, would you feel more comfortable if I took my self leveling a little deeper to the point where I would have a thin coverage everywhere and proceeded with a over cement install instead of an over wood install? I’d have to see how deep that takes me but I think I would still be pretty close to flush at the door transition. My low point is the far corner.
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Unread 03-21-2020, 08:13 PM   #24
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Robin, the disclaimer at the end of most of my posts is there for a reason. People bond all sorts of tile substrates to OSB out there every day. I don't favor it. That doesn't mean you shouldn't do it, just means I don't think it's a real good idea.

As for your SLC, that would also be between you and the SLC manufacturer. I know there are some manufacturers that indicate their products with no reinforcing mesh down to feather edge over wood framed floors, which I presume includes OSB, and I don't think that's a good idea, either, but that doesn't mean you can't do it.

Read and follow the product manufacturers' instructions. That trumps any opinions you get on the ol' Internet from people not known to you, eh?

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Unread 03-21-2020, 08:15 PM   #25
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What would concern me is that you'd still have a single layer of 5/8" OSB to hold up everything. If you add a layer of 1/2" plywood, you can bond Ditra directly to it with the appropriate mortar and have no problems with deflection or adhesion.
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Unread 03-21-2020, 08:26 PM   #26
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I was thinking the same as Kevin. I'd add the plywood, that would add more strength and give you a good surface to bond to.
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Unread 03-22-2020, 09:01 AM   #27
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Thanks all, for dragging me to the right conclusion. I’ll add ply! Last question. I never noticed it before the demo, but there is a significant dip on the right and side. Before I removed the floor I drew a line above where the molding line would be if I let it follow the floor. You can see it but I measured too - It dips 1/4” over 3’ and bugs me. (My wall tiles are definitely level). This will be behind the toilet, in a kid’s bathroom and my husband keeps reminding me no one will ever care ... but ...

If I was to try to level this, would you do it before or after adding the ply? I don’t know if there are screws that would go through mortar & wood and I guess after would mean that I’ve got a better chance of bonding since it would be Ply not OSB? Is there a technique I could use to level the floor before adding the ply (that doesn’t involve ripping up the current OSB? I have more research to do about exactly where the problem is but it seems like it is in the tub section only. As I get to the door/vanity area I’m level.

Thanks all -
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Unread 03-22-2020, 09:11 AM   #28
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Unless you are willing to make the adjustment at the top of the joists, you must do it after you add the second layer of subflooring.

One of those situations where you might, just this once, agree that your husband could be at least partially right. It's not common, but it has happened before.

Your floor tiles don't care if the floor is level, they care only that it's sufficiently flat. Unless your tiles are to be of large format, you may be able to live with the situation as it stands. If not, there are cementitious patching materials that you might be able to use to flatten out a small area such as that.

Now is also the time to consider whether you'll need to raise the toilet drain flange. The proper height is to have the flange on top of the finished flooring. There are way to compensate if it's not correctly installed, but the proper installation is the best approach.

My opinion; worth price charged.
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Unread 03-22-2020, 09:16 AM   #29
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I take it back! You don’t visibly see the dip the way you do in that one corner, but it is not level. My wildly uneducated guess is that the left joist is higher than the right?

I’m not sure if you can see the gap, but here is a pic. Also shows some of the clean up I still have to do!
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Unread 03-22-2020, 09:23 AM   #30
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Oh dear lord, this is the worst news I’ve received since seeing water drip through my kitchen cabinet moulding after asking a decent plumber to check and make sure my tub drain was set properly. My husband has a point. Hmmmm. Must block him from this site forever.

So, abandon the 1/2 chisel and 1 hr per sq ft clean up schedule, get some ply & get on with it. Appreciate the advice and therapy sessions!
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