Ceramic tile subfloor

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  #1  
Old 04-25-11, 03:49 PM
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Ceramic tile subfloor

Hi all,
I was hoping to install ceramic or porcelain tile in my kitchen but have a concern about the subfloor. Deflection numbers are okay, 2x8 joists,16oc with about a 10ft span. Subfloor is 7/8 x 3 1/4 tongue & groove planks. I believe that the minimum recommended thickness for ceramic install is 1 1/4" which means I would have to add a minimum of 3/8 ply correct? If I do this, my kitchen floor will be 1/8 higher than my floors in the dining room and hallway to start with. By the time I add Ditra (1/8") and tile (1/4") my kitchen will be a full 1/2" higher than the ajoining floors. Anybody out there ever had a 1/2" transition in a floor and been able to live with it? Would I be able to go with a 1/4" ply instead of 3/8" or am I asking for trouble with cracking tile and grout? I think my only other viable option would be to go with a groutable peel n stick but I am a little leary about how well that would hold up especially when dragging a 400lb fridge across it. Any suggestions are greatly appreciated.

Thank you
 
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  #2  
Old 04-25-11, 10:29 PM
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If you had a 3/4 plywood subfloor you might get away with only Ditra, but with T&G planking you really need at the very least the 3/8 construction grade plywood on top. The concern is not only the thickness of the floor but the planking verses a sheeted floor. It sounds like your issue is around what you are transitioning to. If it was 3/4 hardwood for example it would work out. Same with some carpets and underpadding. Would it be possible to do the kitchen floor the right trouble free way now, live with a transitional height difference for a while using some kind of transition strip, and then consider also changing the other floors later on with a product that matches closer to the tile height? If the kitchen floor is not prepped correctly you are right in your thoughts of tile and grout cracking.
 
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Old 04-27-11, 12:47 PM
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The planks are a problem - the best solution might be to remove them and put plywood over the joists, as this will help reduce the overall height of the floor
 
  #4  
Old 04-27-11, 02:06 PM
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Martin

Its not uncommon for the finished height of ceramic tile floors to be 1/2" or more higher than the floors they transition to. Ceramic tile needs a stronger, stiffer floor structure than other flooring materials.

The plank flooring is very unstable, as each plank moves independently with season moisture and temperature changes. You should add at least a 1/2" of exterior glue bc plywood over the planks, then an isolation membrane like ditra. You may be able to use 3/8" plywood, but I'd recommend the 1/2". To directly answer your question about 1/4" plywood, no you cannot use any 1/4" wood products as underlayment for ceramic tile.

Depending on the floors you are transitioning to, there are solutions that look good and function well.
 
  #5  
Old 04-27-11, 07:59 PM
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I believe that the minimum recommended thickness for ceramic install is 1 1/4" which means I would have to add a minimum of 3/8 ply correct?
No, that's not right. The 1 1/4" is if you were tiling directly on the plywood, (which would be a really bad idea). You can tile even when the subfloor is as thin as 5/8". Just add a concrete backer or a membrane such as Ditra.

You need to add plywood because of the plank subfloor, as already stated. I also recommend 1/2" b/c, 3/8" will not do the job. Be sure to refasten all the planks, and replace any planks that need it.

Anybody out there ever had a 1/2" transition in a floor and been able to live with it?
!/2" is nothing, not a problem in residential use. Remember in a commercial application we try not to do that cuz there are people looking to take a dive, or because of strange environment people are likely to stub a toe......and find a lawyer. You can always put tile everywhere like in commercial applications and most of the homes on earth.

Jaz
 
  #6  
Old 04-29-11, 08:46 PM
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Thumbs up Thanks

Hey guys,
Thanks for the great responses. I have already bought 1,000 floor screws so I can tighten up all the planks to the joists and will probably go with the 1/2 in ply just to be sure. I'm sure I can find a reducer that will fit the bill.

Martin
 
  #7  
Old 04-29-11, 08:54 PM
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will probably go with the 1/2 in ply just to be sure.
Good plan, but it's not to be "sure". 1/2" over those wide planks is the minimum. Make sure you use 3 screws at every joist.

Jaz
 
  #8  
Old 05-12-11, 07:21 PM
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Hi again guys. Wodering which way to lay my plywood. If I lay it perpendicular to the joists ,it will be the same as direction as my t&g subfloor. Is this okay or shoud I lay it perpendicular to the t&g?? Also can I use builders grade plywood or do I need to spend the extra for one finished side. If I buy the finished one, I assume the nice side would be face up?
Thanks again
 
  #9  
Old 05-13-11, 11:22 AM
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The plywood should go perpendicular to the floor joists. Use exterior glue plywood, cc plugged or better, minimum 1/2".
 
  #10  
Old 05-13-11, 12:07 PM
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The rougher the plywood surface the better the thinset grip.
 
  #11  
Old 05-13-11, 03:39 PM
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The rougher the plywood surface the better the thinset grip.
What? nah......... All plywood is porous. Plus I hope the tiles are not being bonded to plywood. We already spoke about that above. C/C or better is minimum, you'll probably find B/C much easier though. Just don't buy the "rough" CDX stuff.

As Johnny said always install plywood across the joists,but of course stagger the seams.

Jaz
 
  #12  
Old 05-14-11, 11:34 AM
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Using Ditra over the plywood. I asked about smooth or rough side up because I saw a video with the installer saying to put rough side up but the guy at Home Depot said smooth side up or I would have to fill in and smooth out any knotholes etc anyway. I believe I need to allow about 1/8 between joints for expansion etc but is it the same around the perimeter? Do I need to avoid getting any mortar between the joints?
 
  #13  
Old 05-14-11, 12:52 PM
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Using Ditra over the plywood.
Good move!

The best side always goes up. Be sure to buy the proper grade for floors because cheap grades such as "sheathing" may have voids in the middle layers since it is not for floors.

1/8" gap between sheets and at least 1/4" around the perimeter and all solid objects. as far as filling the gaps, obviously leave the perimeter open. The between the sheets gaps is another matter. Read what the thin set bag says about that. Some say to fill it, others say to leave them open. Some may avoid the subject. If you're confused about what to do, maybe fill with caulk.
 
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