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Old 03-03-2012, 11:18 AM   #1
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Plywood knotholes


Hi. I am tiling a BR floor, and have placed 1/2" CDX PW over 2x6 t&g sub floor. There are a few 1 ply deep open knotholes in a small section on the pw. Would it be best to fill these with a filler, like "fix it all" or would the quickset I will put between the cbu and pw, fill it ok? Thanks

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Old 03-03-2012, 01:00 PM   #2
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Plywood knotholes


Hi,

That's one of the reasons you're not supposed to be using CDX as an underlayment. It's called "sheathing" for a reason.

But, now that it's done......... I think you'll be OK in this case as is if you otherwise installed it correctly. Did you butt the sheets together or are there gaps? Any gaps around the perimeter?

Just to double check, did you check a span chart to make sure the joists meet minimum specs? What type of tile and thin set will you be using? Please be specific.

Jaz

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Old 03-03-2012, 06:55 PM   #3
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Plywood knotholes


This is how they use to lay tile before cement board came along. It's still done to this day.
CDX is fine to tile on...when you have
3/4" ply under 1/2" staggered correctly.
The reason we put cement board or a membrane like a ditra so just in case the tile and or grout fails.
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Old 03-03-2012, 07:12 PM   #4
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Plywood knotholes


Wow. Just wow. And I LIKE tiling over plywood!! But wow!
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Old 03-03-2012, 07:49 PM   #5
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Plywood knotholes


Where did that knowledge come from?

Plywood expands ans contracts at a different rate than tile--frequently breaking the bond that holds the tile--

that is why a backer board is used or a mat system like Ditra.
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Old 03-03-2012, 07:51 PM   #6
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Mike, it IS entirely possible to do an interior installation directly over plywood, and have a good strong floor. In fact, TCNA even has a method listed for it (F-149). However, there's alot more to it than what the TCNA lists.
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Old 03-03-2012, 07:55 PM   #7
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Hey Jet,

I'd rather not be a pain in your side all the time...... but...........

Quote:
The reason we put cement board or a membrane like a ditra so just in case the tile and or grout fails.
This makes no sense to some of us. Have you read something different?

In case you also missed it, the OP mentioned surface voids. But CDX also has voids in the center plies. That is why it's called sheathing. It's ok for outdoor use like to nail vinyl siding to or many other uses where voids and splits don't matter.

Tiling over plywood is not something I'd recommend to anyone unless you take certain precautions and also use specific products. What's your thoughts on the joists system?

Jaz
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Old 03-03-2012, 08:29 PM   #8
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Plywood knotholes


Plywood knotholes-image-3270123902.jpg

This is cdx I Tile on. the op might have the wrong ply being used. If it looks anything like this he is fine to use.
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Old 03-03-2012, 08:55 PM   #9
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Plywood knotholes


Quote:
Originally Posted by JazMan
Hey Jet,

I'd rather not be a pain in your side all the time...... but...........
Jaz, do you listen, or play Jazz?

Quote:
Originally Posted by JazMan
This makes no sense to some of us. Have you read something different?
I have been around the block to know a thing or two.

Quote:
Originally Posted by JazMan
In case you also missed it, the OP mentioned surface voids. But CDX also has voids in the center plies. That is why it's called sheathing. It's ok for outdoor use like to nail vinyl siding to or many other uses where voids and splits don't matter.
Some CDX sheets are crap to use and should be only used for roofs or house siding.
A good pine look like in my photo I posted if you have a nickel size void indent make shore the morter gets in there good won't have issues.

Quote:
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Tiling over plywood is not something I'd recommend to anyone unless you take certain precautions and also use specific products. What's your thoughts on the joists system?
Jaz
And what exactly did you use to tile on back in the day Jaz & I'm not talking about the 90s.
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Old 03-03-2012, 08:56 PM   #10
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Plywood knotholes


Is that mastic you used in the tub?--I question your knowledge of the best accepted methods for tile installations,
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Old 03-03-2012, 09:05 PM   #11
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Quote:
Originally Posted by oh'mike
Is that mastic you used in the tub?--I question your knowledge of the best accepted methods for tile installations,
I'm sorry to hear about that Mike.
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Old 03-03-2012, 09:57 PM   #12
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Quote:
I'm sorry to hear about that Mike.
OK, you're forgiven, Now you know you shouldn't be using bubble gum in wet areas if you really want to do the best job possible for the client.

Quote:
I have been around the block to know a thing or two.
I understand totally. We know what we know. Sometimes we don't know and don't know that we don't know.

I don't think there are some CDX that are better than others. CDX is the grade. None of it should be used as an underlayment. I know it's done all the time though. It's very tempting when the sign says it's half the price of the right stuff. After all, who's gonna know the difference once it's covered?

In the old old days tiling over mud was the only option. Then later when DIY started to hit the industry there were many jobs installed over ply. At first we had only mastic, and epoxy. Epoxy was too expensive and difficult to work with. Many floors were done with mastic, although the mastics back then were much better than those of today. Solvent based, flammable etc. Then in the '70's better products were developed for the DIY market. Thin set mixed with "milk".

Also in the 70's Wonderboard was developed and some people started using that. It wasn't easy to sell since we had to charge $18 a sheet. We went through a learning curve as to how to install it cuz at first we only recommended construction adhesive from a tube plus roofing nails. Later we learned it had to be bedded into full spread of thin set mortar and taped. etc .................

Jaz
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Old 03-03-2012, 10:21 PM   #13
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Plywood knotholes


Bubble gum!! Am I suppose to tip the waitress as well? lol
My tile jobs still stand strong to this day.
They wouldn't make tile glue if it doesn't work.
Doesn't mean I don't use thinset I use both and yes tile glue is easier to move around.
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Old 03-04-2012, 09:30 AM   #14
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Plywood knotholes


Thanks for answering. The cdx was all I could find locally for x pw. It looks good except for a section of one sheet that has the mentioned knots. The sub floor is 2x6 t+g over 4' oc 4x8 beams on posts. I do plan on using 1/4" cbu over the pw, which I will cover with modified thinset. My question is , do you think the thinset will fill the open areas, or would I be better off filling them with say fix all, prior to the thinset application? I did leave 1/8 gap between sheets and 1/4 perimeter, and will also do the same with the cbu. Thanks.
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Old 03-04-2012, 09:53 AM   #15
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Yes the thinset used to embed the backer will fill the open knots---nail or screw according to the manufactures instructions.--Good luck---Mike---

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