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mardee
02-20-2008, 07:11 PM
Our Deflecto Calculation gave us an L/1520. That's with using 2X8 floor joists with girder support every 6 feet in our kitchen. Our existing subfloor is 3/4 X 7 1/2 redwood planking. Not T&G. The planking is spongy in most areas in between joists. Is our best option to remove the planking and go with two layers of 5/8 T&G plywood, or two layers of 3/4 ply or leave the planking and go with one layer of 3/4 over planking? Finally, should we put 1/4 hardiboard over the ply, and is thinset necessary or just anchored with screws ok? Thanks for any help...Mardee

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Brian in San Diego
02-20-2008, 08:33 PM
Mardee,

Welcome to the forum! You have a very stout joist system if you have support under the floor joists at 6' intervals. Are your joists on 16" centers? I don't like the sound of spongy. If there's a little "give" that might be different. You haven't told us what you'll be putting on this floor. By what I'm reading it seems like you're planning on stone of some type. I think if it were mine, I'd take up the subfloor if it's spongy. Then lay down 3/4" plywood (CC or better exposure 1) glued (construction adhesive) and screwed to the joists. I'd top that with 1/2" plywood of the same grade screwed to the 3/4" ply only. Read the thread in the (Liberry) on plywood, cdx, etc. especially the article in post #3. I prefer Ditra over a CBU (hardiebacker) but if you are going to use a CBU it has to be set in a layer of thinset and then screwed down. The thinset is to fill any voids...the screws are to hold it in place.

Brian

mardee
02-20-2008, 09:14 PM
Brian: Thanks for the quick response!

Yes, we have 16" OC joists. We plan to put tile on the floor. We've had a past problem with sponginess so it's critical to make the floor solid. Am I correct in understanding that CDX is not to be used for first layer of 3/4" tongue and groove? Thanks, mardee

Brian in San Diego
02-20-2008, 11:29 PM
Mardee,

No CDX anywhere under a tile installation..to many voids. Also avoid RTD or anything that says "sheathing" on it. I used BC sanded exposure 1 from HD.

Brian

mardee
02-21-2008, 10:15 AM
Brian: Just wanted to say thanks again for your responses. What a great site! I think we're good to go with your suggestions and should have no problems...Thanks, Mardee

poolmaninct
02-21-2008, 01:18 PM
brian, would you elaborate on t\your install method, spacing etc...
ty
ray