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Old 08-21-2007, 11:53 AM   #1
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What should I use between layers of ply

I have a bathroom that I am going to tile using Schulter Ditra. I am going to add 1/2 inch ext plywood to the existing plywood subfloor for height and rigidity reasons.

Should I put rosin paper or 15 lb felt in between the two layers of plywood to make sure there are no squeaks?

Should I glue down the new layer as well as screw it?

Thanks in advance for any and all help.

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Old 08-21-2007, 02:15 PM   #2
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What's the sub layer? You may want to go to 3/4" depending on your floor structure and tiling intentions.

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Old 08-21-2007, 06:23 PM   #3
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If you ensure both the first existing layer of ply is well attached to the joists, then screw the second layer to the first (avoid the joists), you don't need anything in between.
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
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Old 08-22-2007, 08:37 AM   #4
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The first layer is the original subfloor in the whole house. It is 3/4 plywood. It was nailed down, but I have gone through and screwed it to the joists every 10 inches. It is solid.

I was thinking about putting down the 15 lb felt to eliminate the possibility of squeaks between this original layer and the new plywood that I am using as a base for the Ditra.

I was going to screw the secong layer through to the joists also. Should I not do that and only screw into the first layer of ply?

I am putting down 6x6 tile.
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Old 08-22-2007, 08:57 AM   #5
chuck stevenson
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Visit the Liberry.

There is a thread about the second layer of plywood. It explains why you do not screw it into the joists and how to offset the edge joints of the ply.

No curb, walk-in shower.
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Old 08-22-2007, 10:02 AM   #6
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Hi Brian,

I had the same questions as you. Look in the liberry. It has some good info. If you do a search, you'll find a long thread from 2000 or 2001 that goes into a lot of detail, and you end up having some questions answered and some not answered.

Dislcaimer: I'm a DIYer , and can only speak from my limited experience and from what I've read here and there.

First, I don't think you would want ply sandwiched between Ditra and felt. Any moisture that did get into the wood would be trapped.

Screw top ply to subfloor only, do not screw to joists. Another tip was to predrill the top ply before placing screws. This allows the sheet to be pulled tight to the subfloor, leaving no gap from threads catching.

To glue or not to glue, that is the question. Opinions differ, and it's a pretty heated debate; not to mention interesting . I personally would say that the answer to whether or not to glue is...IT DEPENDS! It would depend on your subfloor thickness, joist size, second layer of ply thickness, whether or not you're using a membrane (like Ditra), the size of your project, and what materials you're using for tile. You need to way out the need for a stiff floor to the need to allow the floor to have more flex or compensatory movement. Exactly how that is going to be decided is beyond me. I have a 5/8" subfloor and placed a 1/2" ply on top. I decided to glue the two together because I am using slate, and since I will use Ditra underneath I felt it would provide almost all the uncoupling, even if I did not glue, and I needed the floor to be as stiff as possible. I have also placed a beam under the house for added joist support (make sure you check out the deflection calculator). The other thing is my bathroom is small, only 5' by 8'. So movement would have been minimal, and probably would have been of little benefit to keep the plies uncoupled.

Again, I'm not an expert, and this is what I took from what I have read.

Good luck!

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Old 08-22-2007, 05:15 PM   #7
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Hi Brian,

Just read a couple of threads and you will see what you need/want when putting down the second layer.

In my opinion, I did not put anything between my 2 layers of ply. I listened to these guys/gals on here and my floor is SOLID. I have 3/4 ply and then 1/2 ply, thinset, cbu, thinset and then tile. Jeez, the bathroom is 5x8 and the floor is only 5x5, you can tell the difference in the floor. My kitchen wasn't that solid until I redid it recently just as I did with the bathroom. My friend came by to measure for cabinets and he was impressed at the floor.

just my .02 but keep reading. Let us know how it turns out.

Andrew..but everyone calls me Andy
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Old 11-30-2007, 04:38 PM   #8
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Welcome, Brian.

I've combined your other thread on this floor here. There are still folks responding to your earlier question while this thread indicates you've already made the choice you were asking about. Please bookmark this thread and use it for all your project questions.

I believe this is the article Chuck was referring to and gives good insight into the proper method of installing that second layer.

My opinion; worth price charged.

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