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Unread 01-09-2020, 04:44 PM   #1
tilehack
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I think I got the wrong plywood

Long story, but I have some lovely oak veneer plywood cut to fit and ready to be installed on the floor of my bathroom under some tile. It's Top Choice HPVA Red Oak plywood, interior grade, from big blue.

However, further reading tells me that thinset doesn't like fancy plywood. Do I have any options to salvage this expensive piece of wood? I have some Aquadefense. Can I put a coat of that on first to protect the pretty, fragile veneer?

If I end up getting a new sheet, can anybody suggest the correct 3/4" plywood? I avoided the Plytanium because I thought it was all coated, but that may not be the case. Help!
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Unread 01-09-2020, 05:39 PM   #2
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Use it for something else, but NOT for any kind of sub floor.

You want exterior glue sheathing with no side less than a C grade. So, do not get CDX, which is common in the big box. Get BCX plywood sheathing that is outdoor rated.

I assume you know about how thick your sub floor should be? How about how to orient it? Also, you know how to fasten it?
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Unread 01-09-2020, 05:50 PM   #3
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What about the Plytanium ... thats a rated flooring material.
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Unread 01-09-2020, 06:17 PM   #4
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@speed51133

Subfloor is 1/2" plus new layer, which is 3/4". It's a 5x5.5 space, so one big 4x5 piece and two smaller pieces joined at a joist. I'm using 2.5" wood screws at the joists, and 1 5/8" wood screws everywhere else.

I was going to get "regular" plywood, but all they had in 23/32 was Plytanium, which I thought was coated. The guy didn't know. I figured better was better, and sucked up the cost. A thoughtless decision driven by too many hours traversing a big box home improvement store. Not the first in this project. I'm wide open to suggestions. Thanks!
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Unread 01-09-2020, 06:32 PM   #5
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Plytanium is a brand that is used for many different products. Not sure what you are referring to...
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Unread 01-09-2020, 06:59 PM   #6
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That second layer of ply should NOT be attached to the joists, so those longer screws were a mistake. The top layer should only be attached to the first layer, and that first layer must be installed properly.

If that first layer was really 1/2", that's a problem, as building codes call for it to be at least 5/8". Note, that's a nominal value, after sanding, it's slightly less than 5/8", but more than 1/2".

Then, the ply must be installed with the grain crossing the joists, not along them (not clear how yours was installed).

An oak veneered ply is not a great tile underlayment material. It's very unlikely that the glue is moisture resistant, and as a result, not particularly stable.

Regardless of the size of the room, without knowing the joist structure, it may not be suitable for laying tile.
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Unread 01-09-2020, 07:56 PM   #7
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10-4 on the Plytanium. I may have gotten it confused with DryGuard.

Sorry, 5/8" subfloor.

Good to know about screws. Why no joists?

Joists are spaced at 14", perpendicular to the tub which fills the rest of the space.

I'll put away the can of Aquaseal and go get the right plywood and use the fancy plywood for a nice stool. Appreciate the help, guys!
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Unread 01-09-2020, 08:04 PM   #8
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Drew, you may be thinking of Dry-Ply. It sheds water to some degree, supposedly more than regular plywood.

Typically, the thicker layer of plywood is secured to the joists, and the top layer is usually thinner and secured only to the bottom layer. In your case, 2" screws work great for securing to the joists. But you want screws around 1 1/2" long to secure the top layer to the bottom layer.
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Unread 01-09-2020, 09:17 PM   #9
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Welcome, Drew.

Not to pile on or anything, but if you'll look closely at your veneered plywood you're likely to see that only the veneer is running the long direction of that sheet and the structural face plies are opposite that. Not good structural plywood at all.

And not only is your first layer of subflooring too thin to meet even the most lax building code, but it's not center matched (T&G edges) and I feel sure there is no blocking under the between-joist seams as would be required.

Best thing you can do is remove everything you've got down to the joist tops and start over with an adequate subfloor.

My opinion; worth price charged.
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Unread 01-09-2020, 11:21 PM   #10
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CX he mentioned in post #7 that the subfloor is 5/8".
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Unread 01-09-2020, 11:23 PM   #11
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Well, I didn't see that correction, Kevin. What is it about gettin' old you don't seem to understand?

Not yet ready to hang up all my tools, but maybe I should consider hangin' up the keyboard.
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Unread 01-10-2020, 05:03 AM   #12
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Nope. You aren't ready to hang up anything yet.
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Unread 01-10-2020, 08:53 AM   #13
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If missing a thing or two here and there was the standard for that, I'd have had my keyboard taken away years ago.
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Unread 01-11-2020, 08:56 AM   #14
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Speed-Mike you are correct about the plytanium. I looked it up, it comes 3/8, 1/2, 5/8 and 3/4. Turns out i was thinking about Advantech osb anyway. Used to use that building houses, it was an excellent subfloor. Memory, wherefor art thou?
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Unread 01-11-2020, 09:46 AM   #15
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