screws and second layer of subflooring


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Old 01-28-08, 06:32 PM
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screws and second layer of subflooring

Hi guys,

I have another question. Adding 3/8" plywood to 1/2" existing subfloor for Ditra then tile. (Schluter rep said I would be ok with this setup). I had originally tried using 1" screws but found that they were not holding so I exchanged them for 1 1/4". I know that with the second layer of subflooring I should not be screwing into the joists. I am wondering if I should be concerned about that 1/4" or so coming through both layers into the joist as there should be no or minimal penetration into the joist. What is the definition of "minimal" here?

thanks,

Mark
 
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Old 01-28-08, 06:52 PM
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You will be fine.
 
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Old 01-29-08, 12:48 PM
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Are you sure schluter is comfortable with 3/8" over 1/2" plywood? I havent seen that in their literature and I wouldn't be comfortable with it. Your subfloor should be a minimum of 5/8" t&g plywood. Just my opinion here but I'd go a minimum of 5/8" over 1/2" plywood. Typically, screwing into a 1/2" subfloor is a problem, as the screws tend to strip out because the subfloor ply is to thin. Normally for 2 layers of plywood you'd want to do what you described that is not screw into the joists. I'm not sure thats good advice here though. 1/2" just doesnt have enough meat to it. I think here id want to hit the joists and use longer screws, installing the 5/8" plywood as though it was the only layer of plywood. In this instance, this is what I'd do.

I often tend to be on the conservative side, so maybe Tilebri or Jazman can chime in here as well.
 
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Old 01-29-08, 01:27 PM
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Hi,

Thanks for the response. I had spoken with a regional manager for Schluter on 2 different occasions and he assured me that it would be ok to use the 3/8" on top of the 1/2". I am on 16" spaced joists that are sistered giving me 3" of width on each joist span. In this link the issues of how to attach the second layer of subflooring are discussed and they agree not to screw into the joists to avoid movement transferring from the joists to the second layer. http://www.johnbridge.com/vbulletin/...ad.php?t=58267.

I am going to be using a spacing of 4 inches around the perimeter and 6 inch spacing in the field. I had gotten started a couple of days ago and had noticed some of the screws stripping out so when that happened I just moved it over and tried again. I am wondering about the glue mentioned in that link above. Your thoughts?

thanks,

Mark
 
  #5  
Old 01-29-08, 01:54 PM
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For years I used glue between layers of plywood. I havent for over 3 years now though. Theres much discussion out there and the consensus is that no glue is better. I'm still not comfortable with your particular situation though.
 
 

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