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Old 03-26-2012, 12:42 AM   #1
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Ditra and OSB directly on floorboards... or leave old underlayment?


I am tiling my kitchen area and foyer (18x18 porcelain) and thanks to having read many threads on this forum, I was sold on using Ditra. I am planning on putting it on top of 5/8" Norbord OSB Truflor.

However, after tearing up all the old vinyl floor, and the layer of plywood it was on, I found this layer of old, but intact plywood underlayment. I've attached a photo (looks much worse in the photo) to give a better idea.

Is it recommended I remove this layer, or does it matter if I leave it? I am located in Toronto, BTW.

Thanks in advance!

EDIT: Just asking if I should keep or remove this layer between the floorboards and the OSB substrate... **I am absolutely not planning to install directly on top of this layer.**

(I can't really see it serving any benefit, but I am curious if there are any detrimental aspects of it either.)
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Ditra and OSB directly on floorboards... or leave old underlayment?-floor_domh.jpg  


Last edited by domh; 03-26-2012 at 01:05 PM.
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Old 03-26-2012, 01:42 AM   #2
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Ditra and OSB directly on floorboards... or leave old underlayment?


If the floor is 100% sound and not rotten or flexing, going over it should work. With the cracks, I would put down a vapor barrier under the OSB and under the house. Moisture trapped in the floor could cause problems of rot or mildew later which would damage the tile.
Haven't used Ditra but have read up on it. Concrete underlay would be your better alternative and the correct thickness and mildew resistance type would be best.
The substrate supports the tile and it is better to put in better than to have a failure and have to start over.

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Old 03-26-2012, 01:52 AM   #3
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Ditra and OSB directly on floorboards... or leave old underlayment?


That looks like 1/4 underlayment, not exceptable to be used under tile.
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Old 03-26-2012, 02:18 AM   #4
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Ditra and OSB directly on floorboards... or leave old underlayment?


Quote:
Originally Posted by joecaption View Post
That looks like 1/4 underlayment, not exceptable to be used under tile.
I think you are looking at the tear out. The strip wood with the cracks should be the original floor they are wondering about.
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Old 03-26-2012, 02:21 AM   #5
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Ditra and OSB directly on floorboards... or leave old underlayment?


Quote:
However, after tearing up all the old vinyl floor, and the layer of plywood it was on, I found this layer of old, but intact plywood underlayment. I've attached a photo (looks much worse in the photo) to give a better idea
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Old 03-26-2012, 02:37 AM   #6
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Ditra and OSB directly on floorboards... or leave old underlayment?


Well, musta misread, but what are the boards that have the cracks between them? I figured that was the underlayment (actually the sub-floor) that they were talking about since they mentioned they pulled up vinyl and underlayment the layer under the vinyl couldn't be the strips and there is a smooth piece to the side. They really need to be clearer.
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Old 03-26-2012, 10:13 AM   #7
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Ditra and OSB directly on floorboards... or leave old underlayment?


Sorry for the confusion. I will try to be clearer.

The diagonal boards you see in the photo are the floorboards. They are sitting atop the floor joists. The home was built in 1970, prior to widespread practice of placing plywood on floor joists. So yes, the diagonal boards span from one wall to the adjacent wall, and are nailed directly to the floor joists below.

On top of that is indeed a 1/4" underlay plywood (as seen in the photo). I have no intention of using it as a substrate ( i.e. not intention of putting any tile or mortar directly on this). This is the layer I am asking about removing. It is not present everywhere on the floor because the previous kitchen cabinetry sat directly on top of the floorboards. Also there was a small section of wall removed. The wall frame's toe plate sits directly on the flooboards, and as such, you remove the wall frame, you expose the floorboards, so no underlay there.

On top of the underlay was another lay of plywood (not pictured). I think it was 3/8", possibly 1/4". It's all gone now, so I won't go into further detail other than the fact that it was there, and it sat on top of the 1/4" underlay you see in the photo. This is also the layer on top of which the previous vinyl tiles were glued.

So to reiterate, I will be placing a layer of tongue & groove OSB on the floor, with the ditra installed on top of that OSB.

The question is, should I remove that 1/4" underlay plywood, or must I put the OSB directly on the floorboards? Does it even matter?
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Old 03-26-2012, 10:29 AM   #8
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Ditra and OSB directly on floorboards... or leave old underlayment?


Yes it matters you need to take the 1/4" out like joe said. put your osb down sanded. The reason for thicker wood is because cement board or ditra hold no stability for tile, there put in for protection of ply and a better hold on your tile.

Last edited by JetSwet; 03-26-2012 at 10:40 AM.
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Old 03-26-2012, 10:36 AM   #9
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Ditra and OSB directly on floorboards... or leave old underlayment?


It wouldn't be a bad idea to pull it up in order to fasten the plank subfloor to the joists. Then screw your osb to the planks and you are all set!
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Old 03-26-2012, 10:41 PM   #10
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Ditra and OSB directly on floorboards... or leave old underlayment?


I agree pull up the 1/4". I don't care for OSB under tile. Prefer cement board. If the floor is solid and no give you may be ok to put down 1/2" exterior ply and cement board. It does provide support to the degree it is supported. All seams and joints must be staggered. Never 4 corners touching. DITRA will decouple the floor but OSB has mold release agents that make adhesion difficult or impossible.
Besure to put thinset UNDER the cement board. Nail underlay and screw cement board down, seal the seams with the proper tape and thinset as well as screw heads.
I would put tar paper over the strip boards to avoid moisture.
You may have more expense but cheaper than having to do it over.
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Old 03-31-2012, 11:29 AM   #11
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Ditra and OSB directly on floorboards... or leave old underlayment?


Thanks very much for all your tips!

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