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Old 01-02-2019, 01:44 PM   #31
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Thomas, your nominal 1/2" plywood is essentially useless for a ceramic tile installation and even more so because it is not T&G style and there is almost surely no blocking under the between-joist seams.

Some substrate manufacturers will accept as little as nominal 5/8ths" T&G plywood over maximum 16" on center joist spacing, but I recommend you start with nothing less than nominal 3/4" material. If you have 16" joist spacing, you can install your substrate material - either CBU or other solid backers or a sheet membrane or something like your StrataMat. I still favor a second layer of plywood subflooring.

If your nominal 1/2" plywood (it's actually barely more than 7/16ths of an inch thick) is in near pristine condition and you want to leave it, you can feasibly glue-laminate a similar thickness plywood over it using a full spread of wood glue and a brazilian screws and get a useful subfloor. Not as simple as it sounds, but it can be done.

Better is to remove what you've got and start over, or leave what you've got and pretend it's not there and install a layer of nominal 3/4" plywood over it, fastening to the joists.

Then your tiling substrate of choice and tile.

My opinion; worth price charged.
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Old 01-02-2019, 05:01 PM   #32
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Since I already have 3/4 plywood sitting in my den, it seems you would suggest placing that down as originally planned on top of the 1/2 plywood and then use cbu over that or as I did before, Strata Mat.

Do I have it right?
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Old 01-02-2019, 07:06 PM   #33
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You could do that.

Actually, what I would recommend is removal of the useless and unwanted half-inch spacer you have and installing a first layer of your nominal 3/4" plywood, but if you have the vertical room to do what you suggest it will work if done correctly and with adequate length fasteners. You still end up with a single layer subfloor in either case.

My opinion; worth price charged.
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Old 01-02-2019, 08:06 PM   #34
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I see. I had, what a combination, 1/2 plywood and 3/4 particle board on top of that. So putting 3/4" plywood back on top of the 1/2 plywood will put me back even with the rest of the floors, and the Strata Matt and tile won't be too much of a change. May be a 1/4" or so transition piece going on to the carpet.

Newer houses I assume have learned to avoid these issues.
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Old 01-02-2019, 08:07 PM   #35
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BTW, I purchased 3" deck screws for securing the 3/4" plywood to the floor joists.
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Old 01-02-2019, 09:27 PM   #36
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Those will work, but 2 1/2" would be more than adequate. The requirement is that the screw penetrate at least 3/4" into the joist.
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Old 01-06-2019, 01:00 PM   #37
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Overthinking or OCD on this flooring?

I've worked on the 1/2" plywood subfloor using DAP's patching leveling compound and figured I had it pretty good using an 8ft level to check. This is a small 10 x 7 room.

So my wife and I worked all day yesterday and cut the 3/4" plywood, cutting around different framing to get it fitting pretty nicely.

Three pieces did it and today looking at getting it up to put rosin paper under it, I spent some more time checking the edges with one another. I picked that boards back up {they were just laid there last night} and see some places I have may be an 1/8" or so where the subfloor is not even. This is running the 8 ft level across the 1/2" subfloor.

So I of course was thinking how do I best fix that? Will the materials that go into tiling above it address that issue if there is one.

Or do I need to put some leveling compound across the whole floor? Like LevelQuik RS 50 lb. Self-Leveling Underlayment? If so how thick should it be? I see the smallest amount is 1/8".

Then I see some people use it entirely as their underlayment, their entire base for tile.

So what to do? Honestly, one of the reasons I hesitated getting rid of that 1/2" plywood in the first place was I could not be sure the floor joists were perfectly level either, not to mention having to cut it all around the room and then have to add structural support for the new subfloor.

I thought about putting roofing felt between the subfloor and the new plywood and add additional layers where their is a slight dip.

We really are talking at the most an 1/8" prior to putting down the plywood. Of course near the edges they don't all meet perfectly even. Slight ridge.

I've said enough. Now I'll listen to the experts.
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Old 01-06-2019, 02:56 PM   #38
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Thomas, were are the 1/8" difference in the 1/2" subfloor, somewhere in the middle, or where one sheet of the 1/2" meets another?
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Old 01-06-2019, 02:58 PM   #39
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Quote:
Originally Posted by Thomas
...and see some places I have may be an 1/8" or so where the subfloor is not even.
Not sure what that means, Thomas.

Keep in mind that if you're not willing to remove the existing half-inch plywood and flatten the joist tops, you're gonna hafta install the new 3/4-inch plywood as though the half-inch material is not there. Then you will need to do any necessary flattening on top of the new subfloor. Probably better to remove what you've got and start over, but that's up to you.

My opinion; worth price charged.
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Old 01-07-2019, 06:22 PM   #40
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I truly respect your thoughts on pulling up the subfloor. But everyman has his limits. I've done that once before in a small area, and I frankly feel I have put too much work into the subfloor including additional bracing in the crawlspace to pull it up. Between the cold weather now in the crawlspace, and the labor involved in fixing the joists, I don't have the will to go to that level.

So I am left with pouring something like Henry 555 Level Pro 40 lb. Self-Leveling Underlayment on top of it which from the reviews works as a good substrate for tile work; or in the bulk of the area put back down linoleum, tiling above the shower walls only.

I have $100 in the 3/4 plywood but if Henry 555 will get me there I am willing to count that as a lesson in learning. I do know when I took up the old tile, they had this 1.5" or so layer of 'concrete with mesh underneath.' I don't believe it was Henry 555 but some trade work of the installer.

So pardoning my lack of will-power to pull up that subfloor, does Henry 555 or another alternative offer a viable solution to my problem? I did some patching again tonight and I realized I just cannot get it smooth and level all the way across. I know the 3/4 plywood would absorb some of the problem, but I don't want to mask it either if that is what I would be doing.

If I ever buy another house, I will look at the subfloor and underlayment before purchasing. These floors have been my most difficult challenge between tiling and laminate flooring. Ugh. I feel old tonight.
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Old 01-07-2019, 08:50 PM   #41
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Thomas, I fully understand your reluctance to remove the existing subflooring, but it's just not suitable for anything, really. I think the death penalty would be a bit lenient for any builder who would install such a product in that application. Just the lack of T&G edges (and you may be sure there's no blocking under those joints) would render it unsuitable even for carpet far as I'm concerned.

And if you'll read the installation instructions for that Henry 555 you wanna use, you'll see that Mr. Henry doesn't find it suitable, either.

Technically, you can't even do a reinforced mud bed over that subfloor.

The only possible alternative to the single layer 3/4" subfloor on top of your 1/2" spacer is the glue-laminated additional 1/2" layer of plywood I mentioned in post 31. But it doesn't sound like your existing subfloor is in suitable condition for that.

Your house, your floor, your choice, of course.

My opinion; worth price charged.
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Old 01-11-2019, 12:48 PM   #42
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Progress! Working on hands and knees for days, I've been able to level the subfloor and with the new 3/4 plywood on top, even my wife is amazed at how level the floor is now.

Moving to the next steps. Hope to put up Hardie board soon. Last time used Redguard. Looks like plastic membrane is also recommended. Pros or cons?

If plastic I assume it goes behind CBU. Do not the screws defeat it's purpose? A bunch of holes where the screws hold the CBU against the studs. If that is a non-issue, what type plastic and how many mils?

CBU over flange, 1/4 from shower base and inside tiling flange by shimming studs. Have that right?

"Green" drywall above shower head walls is acceptable and correct as well I understand.

Thank you for your time and and patience!
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Old 01-11-2019, 04:15 PM   #43
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1. Yes, the moisture barrier goes directly onto the wall studs behind the backer board. While the mechanical fasteners do penetrate the moisture barrier, it still works just fine in that application.

You can use a polyethylene membrane of at least 4 mils thickness or you can use 15 pound roofing felt. I find the poly much easier to work with in that application.

2. That is the preferred method.

3. There is no need for any color of drywall other than white in your application.

My opinion; worth price charged.
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Old 01-12-2019, 02:50 PM   #44
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Thank you!

Brings up two questions. 1) in on the theory. With the water proofing membrane behind the CBU board, that means any moisture would go through the CBU, hit the plastic membrane and then run down {in theory.} Which means once it is at the bottom, if one caulks the seam from the shower base to the tile, the moisture is trapped.

It would seem putting a moisture barrier in front of the CBU, like Redguard, would avoid that issue. Just understanding the theory on this question.

2) I went with a Acrylic shower base which has a tiling flange. It fits in my opening with a 1/2" space on all three sides. I assume I need to shim my studs on all three sides right above the flange, flush with it, and then the CBU board would then hang right the shower tiling flange.

In doing that, I will have a 1/2" gap from where the drywall meets the CBU board. I assume some tile pieces will cover over those corners?

My wife wondered about putting the shower base right up to one wall rather than centering it. While it would be less shimming by one wall, centering it in the opening seems to appeal to me the most.
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Old 01-12-2019, 05:33 PM   #45
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1. In either case you would have the same situation. If you achieve 100 percent thinset mortar coverage on the back of each of your tiles over a direct bonded waterproofing membrane (you won't), the problem would be substantially reduced, but I have long advocated for either not caulking the tub/tile joint or at least leaving some weep holes in the caulking you do use there. That does not comply with the tile industry standards, though.

2. Not sure I understand your question, 'specially the part that says, "I assume I need to shim my studs on all three sides right above the flange, flush with it, and then the CBU board would then hang right the shower tiling flange."

Not sure what you are flushing up to (which side of the flange or the top or...) nor where your CBU would hang. Little help with that, please.

My opinion; worth price charged.
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