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Unread 02-02-2020, 10:12 AM   #16
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Would be comforting to see a grade stamp, James, if you wanna look on the other side of your panels. But looking at your photos the top ply does not appear to be a thin hardwood veneer of any kind and the panel edges are T&G, which would be characteristic of an exterior glue panel to my thinking. That's the primary basis for my assessment and could be wrong.

I would still be concerned with the condition of the plywood and if you're not absolutely sure it's nominal 3/4" rather than only nominal 5/8ths" material, it may be OK. I wouldn't personally tile over a single layer of nominal 5/8ths" plywood in perfect condition and in the condition I see in your photos I would absolutely not recommend it for a tile installation unless it were nominal 3/4" [/b] at least[/b], no matter what grade or exposure rating. But that's:

My opinion; worth price charged.
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Unread 02-02-2020, 10:21 AM   #17
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Thank you CX.

I am sure it is 3/4, just not sure exterior or not. Would it make sense to put the plywood I mentioned a bit earlier in the thread over the current plywood (item # 12231 at Lowes - Plytanium 11/32 CAT PS1-09 Square Structural Plywood Pine - BCX rating). Main concern with adding additional plywood is just getting into height constraints with door openings.
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Unread 02-02-2020, 02:09 PM   #18
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I'm always in favor of more than a single layer of wood subflooring, James, but especially when the existing is in questionable condition. And keep in mind that all the testing done to determine the minimum subfloor thickness for any tile assembly is done with new material, in pristine condition, near perfectly installed over joists with zero deflection and the test needs pass only one time.

I don't like your nominal 3/8ths" plywood as a second layer as the material I usually see available is rarely sufficiently flat and can't be effectively installed flat to the first layer. I favor nominal 1/2" plywood for the second layer.

As for your doors, if they're interior it's a very simple matter to cut them to fit new flooring material and you'll most likely need to be cutting your jambs and casings to fit the new tile floor anyway. Exterior doors can be more problematic, of course.

My opinion; worth price charged.
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Unread 02-03-2020, 09:01 PM   #19
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Thanks again CX, great information.

I realize I will need to cut the door jambs either way, but the main concern height wise is on my garage door and my exterior door (to rear deck). I have 1.3 to play with after the removal of the current luan plywood and sheet vinyl.

My calculations at this point are as follows:
- Tile 8 mm = .31 inch
- CBU = .25 inch
- Mortar under CBU at 1/4 U notch trowel = .125 inch
- Mortar under tile at 1/2 U notch trowel = .25 inch
- Total after these = .945
- IF I add the 1/2 plywood = 1.445 (well above what I can do)

So the options on the install that I am comfortable with:
Option 1: Install 1/2 plywood and NOT put down thinset under the CBU (this will be cutting it very close height wise)
Option 2: Do everything above without install 1/2 plywood on top of my current subfloor.
Option 3: Install a plywood that is less in thickness than 1/2 and perform all of above steps.

I'd love to add the .5 plywood to the 3/4 (I'd give it like a 6 or 7 out of 10 on the perfection scale) just doesn't seem like I can pull it off. I could replace the current 3/4 with new 3/4 or even something thicker, just a bit hesitant as I don't have the skill when it comes to load bearing.
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Unread 02-03-2020, 09:55 PM   #20
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I understand your concerns, James. Couple points:

You could use a sheet membrane or even an uncoupling membrane and shave 1/8th" or more from your CBU underlayment.

You will not have 1/8" of mortar under any of the membranes. Perhaps 1/16ths" or a bit less.

The nominal 1/2" plywood is closer to 7/16ths" thick than to a full 1/2" thick.

You don't need, nor will you likely have, a quarter-inch of mortar under your set tiles using a 1/2" square notch trowel, and if your tiles are flat and your substrate is flat, you don't need a 1/2" square notched trowel.

The nominal 3/8ths" exterior glue plywood is the minimum you can use in your appliction and if you can find some that's sufficiently flat and you think you can get it installed even flatter, you can certainly use that if you want.

I would not recommend you bond directly to a plywood substrate, but if your existing subfloor is properly installed, (I usually say in good condition here), and you install your second layer of minimum nomilal 1/2" material corrrectly, you can technically do so. We (TYW) generally don't recommend that installation method because it is very intolerant of any deficiencies.

All up to you, of course.

My opinion; worth price charged.
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Unread 02-09-2020, 04:49 PM   #21
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Awesome feedback as always CX.

I have been able to find some stamping on my plywood -- I have attached pics, but it is nomial 3/4 Georgia Pacific Sturd-I-Floor T&G Exposure 1. That said, I wanted to ensure Exposure 1 was going to be sufficient to handle the thinset under the backerboard especially in those areas that have a few cuts and are deeper than the exterior layer. If so, I do not believe I will add any additional plywood.

Also, the remaining question I have is product related (if you can't answer due to restrictions etc. I fully understand). I have access to Home Depot, Lowes, Floor and Decor. So my backerboard options are Hardie, PermaBase, Durock, Durock Next Gen, FiberRock, and Wonderboard. Since this is my first install, and I am not 100% confident I will do an amazing job, are there any particular CBUs that have a bit more forgiveness than others?

Thanks again for all of the feedback, plan to rock and roll on this once I get 2-3 days to knock it out.
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Unread 02-09-2020, 04:50 PM   #22
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plywood pics
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Unread 02-09-2020, 05:16 PM   #23
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Exposure 1 is an adequate exposure rating for your application, James.

As for restrictions on mentioning manufacturer names, we have none here. Everyone says whatever he wants about whatever he wants so long as he does it in a civil manner.

Which CBU is a Ford/Chevy/Dodge truck kinda thing. Each of those who use the stuff has a favorite and one man's favorite is another man's last possible choice.

My only comment would be about Hardiebacker, which is a good product but hard and dense and very unforgiving of any error in installation. Do a good installation and it works just fine according to the reports I've seen here over the years. I've used their exterior siding a good bit, but never actually installed the Hardiebacker on a floor.

Wonderboard is too flimsy and crumbly for my taste, but I've heard other call it a favorite.

You now know perhaps a little more than I on the matter of CBU tile floor substrates.

My opinion; worth price charged.
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Unread 02-09-2020, 05:38 PM   #24
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Great, thanks again CX! I really appreciate all of your feedback/assistance.

I am likely going to go with PermaBase as I have seen many good reviews for them.

Last questions, seriously this time....Would you recommend setting the CBU in perpendicular, parallel, or it really doesn't matter direction with joists. Also, is it more forgiving to have a thinner or thicker mortar line?
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Unread 02-09-2020, 06:16 PM   #25
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It doesn't particularly matter since it isn't a structural component. With that said I would probably go perpendicular to the joist but not for any logical reason.

Not sure what you mean by mortar line.
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Unread 02-09-2020, 06:35 PM   #26
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Ah shoot, meant grout. Not mortar.
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Unread 02-10-2020, 06:45 AM   #27
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Thicker grout lines are more forgiving, James, gives more wiggle room since the adjoining tile edges are farther away from each other thus making minor alignment issues, and even lippage, less apparent to Mrs. James' eye, thereby avoiding side eye.
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Unread 02-10-2020, 08:20 AM   #28
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HAHA - Thanks Dan, that was very well said!

Alright guys, I appreciate all of the great feedback! I will post pics when I finish up with this project!
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Unread 02-12-2020, 12:41 PM   #29
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I'm back....with more questions....

So after pricing out all the materials, etc. and I came across both Ditra and Strata Mat -- just as I was about to pull the trigger on purchases using CBU...go figure.

So my areas, once again, this flooring is going to be for kitchen, couple of short halls, and laundry room over my crawl space and subfloor of 3/4 exposure 1 plywood. I am not concerned with having waterproofing.

Mainly, why the Ditra and Strata Mat stuck out to me is from an ease of install (based on many folks feedback including this great forum) and the fact that that are supposedly a bit more forgiving on cracking.

My main concerns with each:
Ditra - use of unmodified thinset under my tile (12x24), I am definitely no expert at all on thinset, but seems to me that modified results in stronger cure and more flexing (could be way off)

Strata - cost of using modified to set tiles would add up (I am planning on 16 bags for 470 sq ft).

I guess my questions are really around does it make sense to spend the extra money from a performance perspective for either Ditra or Strata or is the extra money really for ease of install.
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Unread 02-12-2020, 01:09 PM   #30
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James, consider this when asking those questions: The ceramic tile industry has no standard for uncoupling membranes, which is what both those products are advertised to be.

Is one better than the other? Without any standard or test method for comparison, no one knows.

As for the type of thinset mortar to be used, the real advantage to the use of a modified mortar would be in workability, pot life, and open time. When being wowed by the bonding strength of the various mortars, keep in mind that the bonding requirement for the uncoupling membranes - a very recent update in the industry - is that the membrane must be able to exhibit a shear bond of 50 psi. If you pay extra for a thinset mortar that advertises a shear bond of 300 psi, the membrane is still required only a 50 psi bond. If you were to ignore the manufacturer's warranties, you could use the same mortar, modified or unmodified, on each of those membranes and you'd still have a 50 psi shear bond requirement.

The membranes are easier to work with than CBUs and may (or may not) provide a bit more isolation of your tile installation from your subfloor, but no one can actually demonstrate that with any officially sanctioned testing I'm aware of. Some of us have been hoping for an actual ANSI standard for those products for a very long time, but I don't know that we're any closer than we were ten years ago.

The choice is entirely up to you.

My opinion; worth price charged.
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