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Discussion Starter #1
Hello,

I bought my house 8 years ago from a builder. As part of the purchase, I had the builder rough out the 3rd floor to be finished later. Well, its later and I am starting to finish the 3rd floor (attic). While laying out the bathroom getting ready to install walls, I see that the 3/4 OSB floor moved some at some of the joints. When I tried to screw down some of the joints I realized that there is no joist under the joint (along long edge).
Will I have to rip up the floor and reinforce it or can I put down a layer of cement board to reinforce it? I am worried the tile will crack.

Thanks
 

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Tile board does nothing to add strength to a floor.
The floors going to have to come out if there's no joist under butt joint.
It also should have been Advantec 3/4 T & G with constrution advesive on top of the joist. Far better to also screw it down since your doing with tile.
Then a layer of 1/2 Underlayment plywood fastened every 4" on the edges and 6 to 8" in the field.
 

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Just so we are on the same page, I am talking about the tongue and groove portion (long edge) of the OSB, but the butt joint (short side) of the OSB.
 

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Just so we are on the same page, I am talking about the tongue and groove portion (long edge) of the OSB, but the butt joint (short side) of the OSB.
I think you have a typo in your reply.
The way it's worded it's still unclear on where the movement is.
 

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Discussion Starter #5
Typos get ya every time......

The tongue and groove portion where two OSB sheets meet are not on top of a joist. The joists are approx 22" apart and the joints in the OSB are about half way between the two joists (about 11" away from a joist).

Thanks for the reply's
 

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Someone screwed up big time.
There were suppost to be 16 or 24" apart max.
There's just no way to fix that one without removing what's there now and starting over with properly spaced floor joist.
 

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I was confused also, the flooring should go across the joist.
But joints meeting in center of the joist, the tongue & groove spanning the joist should be a span of about 22".

If you have this installed correctly, should not be much if any flex in 22" of the T&G
 

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You have joist spaced at 24 inches---cut out and replace the miss matched sections---then I bet you e=will need another layer of 1/2" bc plywood on top--nailed or screws to ensure enough stiffness for tile---

before you proceed--get us the unsupported length of those joists---the size--typo and spacing (24"?) and someone will run a deflection chart and see if the floor structure is strong enough for tile or stone---
 

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Tileguy
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Subfloors with joist spacing of twenty-four inches requires "two layers" of plywood/OSB if ceramic tile is to be used.

Something doesn't sound correct here. Surely a home builder with the knowledge to complete a homes construction would not use "flying-joints" to install a subfloor. That method would be to no one's advantage.
 
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