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Old 11-26-11, 08:06 AM
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just starting

I just took up my vinyl tile and want to put down some porcelane 17x17. Do I have to put down a cement board first? And what problems might occur if I don't??? The floors are very sturdy hardwood and the building is pretty old!
 
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Old 11-26-11, 09:07 AM
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Not a pro...but here's a few questions they are going to ask. What kind of flooring is there now? How wide and how thick are the boards? What is the spacing of the joists underneath. What are the dimensions of the joists? 2x8, 2x6?

"Very sturdy" and "pretty old" are just subjective...need to have some actual specs to be able to give accurate advice.
 
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Old 11-26-11, 09:53 AM
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Hardwood planks? If so, they might need to come up; they're not a good foundation for tile.

As Vic said, what are the joist size, spacing and unsupported span? What are all the layers of the current floor?
 
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Old 11-26-11, 10:22 AM
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Originally Posted by mitch17 View Post
Hardwood planks? If so, they might need to come up; they're not a good foundation for tile.

As Vic said, what are the joist size, spacing and unsupported span? What are all the layers of the current floor?
The joist are 2x10's ,161/2 inches apart, sitting upon 6x8 cross beams. the hardwood flooring slats are upon a firm layer of 1x12's.
 
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Old 11-26-11, 10:27 AM
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You have hardwood flooring planks on top of other planks, typically not the subfloor you want for tile. I'd tear out to the joists and build back up with plywood and then concrete backer board on top of that.
 
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Old 11-26-11, 11:36 AM
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What about DITRA? Their specs say it can be used over structural plank floors with up to 24" o.c. joists. They require 1/2" OSB over the planks. It's been awhile since I sold ceramic, so I'm a little unfamiliar with it, but they say it virtually eliminates sheer stress. Besides, Mike Holmes loves it!
 
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Old 11-26-11, 11:56 AM
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That certainly sounds easier than my suggestion.
 
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Old 11-26-11, 06:06 PM
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What about DITRA? Their specs say it can be used over structural plank floors with up to 24" o.c. joists.
Oh? Where does it say that? Not true, neither Schluter nor anyone else recommends any membrane or concrete backer board over planks.

The hardwood needs to be removed, the plank subfloor can stay, but you have to install a plywood underlayment over it, then Ditra or the backer board.

If the 1x12" sub is in perfect shape I would re-screw at every joists and install the proper 1/2" or thicker ply underlayment. It's exposure 1 with exterior glued plies. If not perfect you need thicker underlayment. Might be best to remove though.

Jaz
 
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Old 11-29-11, 07:46 AM
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Originally Posted by JazMan View Post
Oh? Where does it say that? Not true, neither Schluter nor anyone else recommends any membrane or concrete backer board over planks.
I often take the time to do some research before I post advice to people looking to spend thousands of dollars on their projects. So, before venturing an opinion, I made sure to consult Schluter's web site.

From Schluter's installation instruction manual:

Floors, Interior - Structural Plank Subfloor
Areas of Application
over structural plank subfloors
interior dry or wet areas
Limitations
minimum 2" x 2" (50 mm x 50 mm) tile
Requirements
maximum spacing of joists is 24" (610 mm)
o.c.
double layer wood floor consisting of:
minimum structural plank subfloor
thickness 3/4" (19 mm)
minimum underlayment thickness -
15/32", 1/2" nom.

While it doesn't specifically mention installation over existing hardwood, over structural plank, I think its worth some further research. As I said, I've never personally worked with this product, but I've heard good things about it. Here's their link: Schluter-DITRA - Schluter-Systems Most manufactures have a technical services department that can tell you if it's necessary to take up the top layer of hardwood.

"the plank subfloor can stay, but you have to install a plywood underlayment over it, then Ditra or the backer board."
So, you actually agree with my original post: "Their specs say it can be used over structural plank floors with up to 24" o.c. joists. They require 1/2" OSB over the planks."
 
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Old 11-29-11, 02:48 PM
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"Structural" says it all.

It does not say existing hardwood flooring.

It would all work, if... installing tiles and backerboard didn't use a lot of water, which creates humidity as it dehydrates, which causes the hardwood flooring to absorb the moisture and swell.... Buckling the hardwood flooring under your, plywood and backerboard and tile. If not buckling, there is going to be some movement. Post completion and seasonal.

Structural has gaps.
Hardwood flooring is installed tight.
 
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Old 11-29-11, 04:48 PM
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OK, just to clarify. I thought staabc was saying Schluter, (or anyone else), was OK to install Ditra directly over the plank subfloor. Of course we all know you shouldn't do that. Just as you can't install Ditra nor a concrete backer over hardwood flooring. As he (?) said, you need a min. 1/2" underlayment over the structural plank subfloor first.

BTW, I do not recommend you use 1/2" OSB, instead use a good quality underlayment grade plywood (not CDX or anything rated as "sheathing".

Jaz
 
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Old 11-30-11, 10:31 AM
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Structural has gaps.
Hardwood flooring is installed tight.[/QUOTE]

I DID NOT think of that. Good point. In fact, Schluter specifies 1/8" gaps between sheets of underlayment.

Jaz, why not OSB? I would think you'd gain dimensional stability as well as a more consistent density. Too rigid? P.S. You can refer to me as MR. Staabc.
 
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Old 11-30-11, 07:08 PM
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You can refer to me as MR. Staabc.
OH, I should refer to you as Mr?

You know Mr. when before you said,

I often take the time to do some research before I post advice to people looking to spend thousands of dollars on their projects. So, before venturing an opinion, I made sure to consult Schluter's web site.
I thought you were being a bit arrogant but just let it go. Now perhaps I was right. Again you're being a wiseguy when you say;

Jaz, why not OSB? I would think you'd gain dimensional stability as well as a more consistent density. Too rigid?
I'd explain to you why not 1/2" OSB, but why bother.

Jaz
 

Last edited by JazMan; 11-30-11 at 07:51 PM.
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Old 12-01-11, 02:48 PM
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"As he (?) said"

Jaz, I was referring to the fact that my screen name doesn't indicate that I am a guy. Maybe I was being to clever for my own good. No offense intended. I am legitimately interested in why you don't like OSB.
 
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Old 12-01-11, 06:44 PM
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OK, sorry if I misread your intensions.

I do not recommend OSB as an underlayment because what I see at the big box stores seems to be of poor quality. I believe it's very porous. I don't think there is a reliable industry standard for OSB underlayment. It's OK for utility or sheathing, but I wouldn't trust it if I'm bonding to it. Matter of fact I know of no one that recommend OSB as "the" underlayment.

I know what you're thinking that some premium OSB's are very highly thought of as the subfloor. I do not disagree with that, but subfloor is a different story.

On the other hand, plywood has a better grading system and as long as people do not cheap-out by buying the cheapo CDX sheathing, all will be good.

There is one reason for OSB's existence, it's cheaper. We've seen it all before with particle board floors and green board for walls. Usually too cheap costs too much.

Jaz
 
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Old 12-02-11, 08:59 AM
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I haven't spent much time reading thinset manufacturers instructions these days, but my recollection is that none of them say that their thinsets can be used over osb. There is plenty of conflict in the industry though as company's like Schluter say that you can use their ditra over osb bonded with modified thinset. I would also choose exterior glue plywood over osb. Its more expensive but also more stable.

Usually too cheap costs too much.
Hey I like that.
 
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Old 12-02-11, 09:35 AM
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Johnny and all,

Here's what I think is Schluter's position about Ditra over OSB using a good quality modified.

We all know OSB is not an acceptable surface to which we can install ceramic tiles on to. Usually the OSB is "the" subfloor, so we wouldn't even consider it. However in an effort to spend less, people consider buying the $8 per sheet stuff instead of buying the correct $22 per sheet underlayment B/C grade exterior glued layers plywood. It's only natural to want to save money.

We believe the well know OSB t&g subfloor is of good quality, but not so sure about their thinner cousins which are not generally used in critical installations. Therefore the * on the bags of thin set that says the mortar can NOT be used over OSB. It's because OSB, while stiff, is not as stable as the correct plywood. Just take a look at new construction when the sheets were not gapped correctly only to see the seams expanded and therefore "peeked". Big trouble.

Ditra works well over OSB because it can "take" the expansion and contraction. It was never about getting thin set to bond to OSB. Modified mortar will bond just fine to it.

Jaz
 
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