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Unread 03-22-2020, 09:30 AM   #31
cx
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You're gonna want the surface of that OSB very clean before installing the new plywood layer, Robin. Chisel (I'd get a much wider one) may help where there are globs of old mortar, but a belt sander, or/and angle grinder might be the tool of choice after that. Something you just hafta decide on site.

Rather than banning your spousal unit, perhaps you could instead get him to assist with at least a bit of the grunt work? Not saying it's required, mind you, just suggesting that it could feasibly be helpful and maybe time saving.

My opinion; worth price charged.
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Unread 03-22-2020, 07:26 PM   #32
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CX, you are a mind reader! I came up to post this pic and ask how concerned I need to be about getting everything off the floor. I assume this is glue from when the original plywood was laid 30ish years ago? Is it a regular practice to trowel it - there are lots of these grooves around. When I install my new plywood should I glue & screw?

While I took ownership of the “whole” bathroom, the floor was a bit of a gut punch. I was going to just correct a few and live with the other mistakes. When it became clear it was a rip-out, he was happy to be a partner in the re-doing. I just had to waste a week waffling & trying to decide what that direction was. I’m pretty sure our marriage will last and we will eventually have a finished bathroom!
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Unread 03-22-2020, 08:39 PM   #33
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I'd get all the screws out, then use an angle grinder with a diamond cup wheel to get the glue off. It may come off well enough with a scraper, I can't tell from your pictures. That would be your call. I know the grinder would be faster and more thorough.

Just set the 1/2" plywood with screws, no glue. When you get to that point, we can post a link to an article that describes the best way to install it.
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Unread 03-23-2020, 07:11 AM   #34
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Ok, I’m feeling stupid, but I am learning! There are so many types of screws! Wood, flooring, construction, etc. - which, and what size, do I want (both to attach the 1/2” ply to the 5/8 as well as strengthen the original nails on the OSB seams?
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Unread 03-23-2020, 08:42 AM   #35
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Your local Homer's will have DeckMate or similar coated decking screws that will suffice. The 1 5/8ths" length will work for both your applications.

My opinion; worth price charged.
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Unread 03-26-2020, 12:06 PM   #36
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Kevin - could you post the link to the article that describes the plywood installation?

Weird update - I assumed I had 16" joists based on the basement and the placement of some of the nails. I had looked at enough nails near the door that 16" made sense and I didn't think much more about it. However, surprise! When I went to screw the existing OSB down in a few places it became clear that some of the nails I was basing my assumption off of are just driven into air. They also hadn't nailed one of the boards along the actual joist. I did a more thorough nail search and drilled some pilot holes and determined that the spacing on the bit of floor I can see is about 10" then 21" (the center distance on those must be off an inch in total is my guess) then back to 16". The short joist spacing lines up straight on the toilet. Feeling better about having to add more ply. The area under the wide joist spacing isn't really a major probelm in the toilet area (in terms of traffic), but it is where you stand while in front of the 4' vanity. Do you think I'm ok with 1.2" ply plus Ditra in this area?

Thanks -

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Unread 03-26-2020, 12:57 PM   #37
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Robin, the link Kevin refers to is in our Liberry under Wood Framed Floors. You should check out the Liberry for other useful information.

The second layer of subfloor article is this one.
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Unread 03-26-2020, 05:36 PM   #38
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Super helpful - thank you. Curious about the 1/4" space at transitions. I understand you want movement/expansion gaps but I'm also thinking of the general advice/importance of no voids. This amount doesn't matter in most spaces since the wall trim will cover it, but what do you generally do at the door and tub? Should I aim to keep the plywood with around 1/4 inch gap at both of these areas and let the tile float a wee bit (get to within 1/8") or would you cut the plywood to get it within about 1/8" of those areas?
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Unread 03-26-2020, 05:52 PM   #39
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You want the gap at all vertical surfaces with all materials, tile included. A color-matched caulk or silicone will work there. I use a T-moulding at doorways between dissimilar surfaces, but you can use caulk at that point as well.
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Unread 03-26-2020, 06:37 PM   #40
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And another question to the one above!

Is it best to have the toilet sit on one solid second layer or does it matter if there is a seam underneath it?

I think I have some leeway about overlapping the existing seam since the area near the tub is only 3'. I was planning on cutting a piece so that the toilet sat on a solid piece BUT ... if I use a full 4' length that gets me perfectly in front of the flange which would make measuring and cutting a dream. This cut takes makes the overlap 30" (18" on the other side).
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Unread 03-26-2020, 06:42 PM   #41
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So long as the support is adequate, it matters not whether the subfloor seam is under the toilet.

You do understand that you want to set the toilet drain flange on top of the finished flooring, though, right?

My opinion; worth price charged.
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Unread 03-26-2020, 07:19 PM   #42
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Ok, great. Yes - I've tried to learn a little about the flange and knew it needed to sit above the finished surface. With my current configuration I will probably be about flush. I'm going to have a professional plumber do everything so I'm hoping they will be able to add a spacer or do whatever they need to make it right. OR - is there something I can/should do now to make it easier on them and have a better result? The current flange is "supported" by 3 free floating 3/4" blocks and it is screwed into the subfloor (the screws span the 3/4" gap without going through any wood blocks. At minimum I was going to try to add more support before putting down the ply, but I haven't really researched it yet! Suggestions?

This is a qustion not a challenge - I so appreciate the right advice I'm gettting! The caulk line needed to cover a 1/4" gap seems huge?! Do larger caulk lines fail easier than smaller ones (even silicone)? I understand the corner near the fixtures is the classic spot for water damage so my untrained brain thinks there has to be a trade off between the two evils (expansion related cracks and water intrusion). I just don't recall a gap that big in any bathroom I've ever seen.
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Unread 03-26-2020, 08:13 PM   #43
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If the top of your WC flange ends up flush with the top of your finished floor, a standard wax ring will usually seal without significant problems. It's not correct, but it's been done successfully many times. This photo shows how the toilet and flange should finish out.

Name:  Toilet Flange Seal Cutaway.jpg
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I'd need a photo to understand what you're telling us about the floor around the flange.

I'm not at all sure what caulk line you're trying to resolve. The 1/4" gap around the perimeter of your subfloor that Kevin recommended needs no treatment of any kind at all. There are other places where you would want a gap that wide in a ceramic tile installation, but I'm not sure what you're talking about in your situation. And while caulking or a flexible sealant can inhibit water intrusion in some cases, if it's in a critical area you do not want to depend upon a flexible sealant as your waterproofing method.

My opinion; worth price charged.
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Unread 03-27-2020, 08:13 AM   #44
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This is what I have now - I don’t know if the wood blocks were new from the last contractor (doubt it) but the screw heads are under the old wax so I assume that was original. My tile is thicker than what I’m replacing plus (the Ditra) so if I don’t address now (or add a spacer) I will be flush without a lot of breathing room for thinset thickness. I can’t run any flooring under the flange because of the screws. Would you cut additional “supports” for under the flange and add a spacer if necessary or is a more drastic fix called for? remove the screws and add wood before rescrewing? Remove the flange entirely And reset/screw through all the flooring?

Sorry for being unclear about the 1/4” gap area in question. I’m talking about where the flooring and tile will butt up against the tub. I know the caulk isn’t really a waterproofing method, but in most modest kid bathrooms, I’d bet there isn’t real waterproofing Underneath and that caulk is the only real subfloor defense against from the water dripping down the side of the tub when kids get out of the bath - that is probably why that corner is prone to rot! I just don’t recall seeing caulk lines that thick in most bathrooms - but I have a pretty small sample! Fundamentally, I guess the question was is a smaller caulk line stronger (will it last longer) than a thicker one. And, if so, was there anything to gain by cheating 1/8” to get the finished tile within 1/8” of the tub vs 1/4”. The last guy had 30% of the tiles actually touching the tub, which even I knew was a total fail. It sounds like 1/4 is what to do - I guess this was more just a question to see if this was an area where “experience” led people to modify the standard at all in the field in consideration of a competing issue (wide caulk at a common water intrusion point).
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