Densshield, wonderboard, detra, schluder???

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Old 02-14-08, 01:58 PM
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Densshield, wonderboard, detra, schluder???

Hello,


I'm planning on putting marble tile in my washroom, and would like to know what product to use under it.
The existing subfloor is 3/4" with a 1/4" pressboard over top. I have screwed ~6" into the joists to keep everything nice and tight.

I'm not sure if I should put a 1/4" cement board (wonderboard), 1/2" densshield, detra, or schluder under the tile to keep it from cracking.

The floor does still squeak a bit, but not nearly as much as it used to. I sistered one of the floor joists with a 2x8 because it was ~1/4" from the subfloor (it must have been installed with the crown facing the wrong way 50 years ago).


Thanks for the help
 
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Old 02-14-08, 02:22 PM
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What is the joist spacing of said floor? What is the unsupported span of these joists? Natural stone requires a very sturdy subfloor.

I'm pretty sure you are gonna need to do some more strengthening.

Natural stone needs a deflection of L720. Here's a handy calculator to determine if your current setup is acceptable. http://www.johnbridge.com/vbulletin/deflecto.pl

If it is, I would use a Ditra or Hardibacker.
 
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Old 02-14-08, 02:33 PM
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Dan

The framing for most floors is adequate for ceramic tile, but not for natural stone. Natural stone requires a floor that is twice as stiff as for ceramic tile. You need to give us all the details for the floor. What is the size of the joists, the unsupported span of the joists, and their on center spacing?

Natural stone also requires 2 layers of plywood totalling 1 1/4" in thickness. This gives the required stiffness between the joists. The 1/4" pressboard has to go, even if you later on decide to use ceramic instead of marble. It cant be used anywhere under tile and has to go.
 
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Old 02-14-08, 02:44 PM
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The word "pressboard" doesn't necessarily tell anyone anything. Maybe we should first define exactly what this product is. Is it partical board made of tiny sawdust looking fibers, or is it oriented strand board made of much larger chips and wafers?

We can't saw it enough so I'll say it again....natural stone requires a subfloor that has twice the strength of what is required for ceramic tile. It is also not a good idea when laying floor panels to fasten the top panel into the floor joists. The floor joists should be delibertly missed with the fasteners.
 
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Old 02-14-08, 03:06 PM
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Bud, I was thinking the same about press board, what is it exactly? I always think of particle board when I hear that terminology but I guess it could be osb as well. Its 1/4" anyways so no good and has to go.
 
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Old 02-14-08, 03:40 PM
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The joists are 2"x8" @ 16" o/c with a span of 11ft.

By pressboard, I meant particle (sawdustboard) board, not OSB
 
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Old 02-14-08, 03:47 PM
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You only have a deflection of L377, not even close for a natural stone.

The particle board definetly has to go.
 
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Old 02-14-08, 03:52 PM
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So if I got rid of the particle board, and put down 1/2" Wonderboard (concrete board), and then the tiles on top of that?
 
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Old 02-14-08, 03:54 PM
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Dan

Your floor joists just are ok for ceramic tile. No way for natural stone. You have a few choices. You can either strengthen the joist system by sistering the existing joists or cutting the 11' span of the joist to something less with a load bearing support wall from below, or you can use ceramic tile instead of natural stone.

As mentioned before you have to remove the particle board. Particle board cant be used anywhere near tile. If you are going ahead with the natural stone then you'll have to add a second layer of 1/2" exterior glue bc plywood. Then either cement board or an isolation membrane.
 
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