Replies

1. 
   chiefclancy | Jan 27, 2003 07:11am | #1

   How big is the bathroom? What is the joist spacing? If it's 16" o.c. or less, you're probably ok, but instead of another layer of ply I would use 1/2" cement board laminated with thinset to the ply and screwed per the mfg's instructions.

2. 
   Frankie | Jan 27, 2003 05:46pm | #2

   Doesn't really matter how big the room is. What matters is how long your span is and what the joist spacing is. You are probably ok for a Bathroom as long as your rough-housing around is limited. Har, har, har!

   You write that you used 3/4" t&g ply. Great!

   What's the 1/2" subfloor on top of it? It should be cement board - glued and screwed to the ply. The tile - installed using thinset - will bond to the cement board better than the cement board (or any other masonry product) to the ply. Therefore the flex/ movement will occur between the cement board and ply. Less oppertunity for tiles (regardless of type) to pop/ crack.

   Go with the marble. Rent a wet saw and use it in the shower/ tub area. Be sure to put plastic on the tiled walls so the spray (water and marble dust) doesn't get on the wall tile grout - easier cleanup.

   Good luck.

1. 
   user-441621 | Jan 28, 2003 02:16am | #3

   i got 1/2 ply on top of the 3/4 i read u need 1 1/8 minimum sub floor for stone . the joist are 2x10  16 oc with 2x6 sistered to the 2x10 . tha span is 17 feet  at five there is a bearing  so the longest unsupported span is 12 feet.walli was thinking of adding ditra or 1/4 hardi backer. the floor is getting tall i want to keep it as low as possible without a failure. i was thinking of just going with the plywood. and a good thinset

3. 
   Frankie | Jan 28, 2003 03:53am | #4

   No hardibacker - it's not rated for floors - and forget the Ditra. It's not needed. 1 1/8" build-up is for stone as in slab. Tile is tile regardless of ceramic or marble at the 1/4" - 3/8" thickness.

   Take off the 1/2" ply and add 1/2" cement board. Use a flex-type thinset which will require the fortifier - sometimes it's built into the dry mix depending on manufacturer. Be sure to back butter the tiles prior to setting.

   Please reread my previous post. The subfloor components aren't suggestions. They're requirements for a proper installation. But that's only based on experience.

   You're thinking about this too much and getting too confused. Keep it simple and think more in terms of sequence and logistics. Take your time. get very comfortable with it. The rest has already been thought out for you and is available on this and other sites and in books. Read and learn.

1. 
   user-441621 | Jan 28, 2003 04:08am | #5

   well that 1/2 is glued. it aint goin  anyplace but on this floor. so how about 1/4 cement board with  thinset. i have used the cbu and also just ply . i think i am over thinkin it i got alot on my plate lately. stairs this week bath floor next.  hardwood after that  etc....etc....etc.. well thanks for the reply my fav sayin 2 heads better than 1

1. 
   chiefclancy | Jan 28, 2003 06:45am | #6

   It's not ideal but you're probably ok with the ply (it is ply, hopefully exterior-grade, and not OSB, right??)

   Make sure whatever thinset you use is approved for use with plywood, and you should be ok. Also, the fasteners for the 1/2" layer shouldn't penetrate into the joists below, and you should stagger the end and edge joints of the 1/2" layer so that they're not directly over the joints in the subfloor.

   Some people will say that installations over plywood are doomed to failure; while it's not ideal, there is a TCA-approved method and in lighter-duty installations not subjected to moisture, plywood installations can work out ok. In a bathroom with heavy marble tiles I'd still go for the 3/4" EGP subfloor with 1/2" durock.. but it sounds like it's too late for that...