Tiling bathroom floor

I have a newly constructed bathroom that has 2x8 floor joists, 16" OC. Covered with 3/4 tongue and groove plywood. I'd like to install floor tiles and have been considering a few of options:
1. tile over 1/2 cement board only 2. put another layer of ply (1/2) over the 3/4 and then tile over 1/4 cement board 3. put another layer of ply (1/2) over the 3/4 and then tile over 1/2 cement board
I would think that option 2 is best because it creates 1 1/4 ply for rigidity and also has the cement board for bonding and waterproof. I would screw both layers into the joists but I'm not sure if I need to put thinset under the cement board since I've heard some yes and some no. What do you think? TIA, Bob
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Bob
Try posting this question at:
http://johnbridge.com/vbulletin/forumdisplay.php?s Ąc49d1c5b7661a7eea1f1e8a0a0e1dc&forumid=1
It is a great tiling site where DYIers and pros discuss tiling issues.
I believe the correct answer would be 2 or 3. definitely not 1. You also want the thinset between the cement board and the plywood. This fills any voids and eliminates flex (which could cause cracks) due to the voids.
Also they seem to recommend that you do not want to screw the plywood to the joists but to the sub floor. Post your question at the site and they will do a better job explaining why.
Also do not use premix thinset! Apparently it is actually modify mastic. Use the thinset that comes in a bag.
Phil

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Thanks! I'll try it there. Bob

options:
cement
cement
would
thinset
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I think options 2 and 3 are overkill, but I'm not a tile setter. I did tile a bathroom with 1/4" wonderboard over 3/4" plywood (2x8 fj. 16"oc) with no problems years ago. The wonderboard was set into thinset and then screwed into place every 6".
--
Jim Sullivan
seattle, washington
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