Replies

1. 
   calvin | Jun 16, 2010 06:17am | #1

   "5/8's flakebd" (osb?)

   is not a good solid base to work from.   I would recommend using plywood on top of that b/4 I'd use cement board.

   Dunc1 should check the Tile Council of America (TCA) for recommended substraits for ceramic tile.  In addition, if the old tile floor showed no cracks or popped tiles-might be a good indicator of what 'works".

1. 
   Clewless1 | Jun 16, 2010 09:41am | #2

   I think my intent was rip out the 'flake board' down to the subfloor and use that as the base for the cement board.

1. 
   calvin | Jun 16, 2010 10:12am | #3

   Clew

   underneath is 5/8" flakeboard + (on top) 5/8" exterior fir plywood.

   I'm not sure what is the subfloor- (if his flake is osb or particle bd).............

   But in either case-5/8 ths is not enough structure under for sure 1/4" nor really enough for 1/2" cement board.  It might work but I wouldn't put my name on it.

2. 
   JTC1 | Jun 16, 2010 05:24pm | #4

   I'm not sure.....

   which is the subfloor (attached directly to floor joists) - is it 5/8" plywood or the "flake board'?

   If the "flake board" is the subfloor - cut it all out and start over - block at the edges for support of new plywood / Advantech.

   Assuming the plywood is the subfloor - you will need to build it up a bit to be stiff enough.  I would refasten the existing plywood to the joists.  Then add a second layer of plywood at 90 degrees to the existing - stagger the joints / seams between old and new.  Laminate the new to the old with PL premium and lots of screws (8" centers or so).  The thickness of the laminated floor is dependent upon the elevation you want to have as final.  I would be comfortable with adding 3/8" plywood on top of the 5/8" for a total floor thickness of 1".

   1/4" cement board is very viable on a floor, I only use 1/2" on a floor if I need to gain the extra elevation.  If tight on vertical clearance then consider Kerdi instead of cement board.  Given the choice between adding hieght with cement board vs adding with plywood, I choose the plywood everytime - the stiffer the floor the better and cement board in any thickness does not add much rigidity.

   I like HardiBacker in 1/4" for floors and 1/2" PermaBase for walls.

   Don't forget to thinset underneath of the HardiBacker on the floor!

   Good luck,

   Jim

3. 
   fingers | Jun 16, 2010 05:49pm | #5

   I think what most here are trying to say is that the stiffness or rigidity of the floor is more important that what you fix the tiles to.

   So if the "flakeboard" and plywood that's already there is solid with no bounce to it, then use whatever you want over it that gives you the right final floor height.  If the flakeboard is falling apart though, it's best to replace it with something stiff like plywood, glued and screwed to the other layer for the maximum stiffness.

4. 
   Dunc1 | Jun 19, 2010 07:59am | #6

   clarify

   Current flooring is plywood on top. The "flakeboard" is just that: handplane-like shavings bound in some sort of resin. There is no particle (sawdust-like component). Looks perhaps somewhat like osb but this is a low-tech version. Floor previously was ceramic tiled (I assume by builder) & lasted 15+ years.

   Given the comments - thanks all - I think it comes down to:

   adding cement board to the existing subfloor - yes or no

   and kerdi membrane - yes or no

   I will have a look at the Tile Institute. Thanks for the ref.

5. 
   DanH | Jun 19, 2010 08:06am | #7

   What's the joist spacing and what size tile are you installing?  1-1/4" floor thickness is marginal for tile, though with reasonably small tile in a small bathroom it's adequate.  You can generally (not speaking code here) have a roughly half-inch difference in floor height without creating a "situation", especially if the lower surface is carpeted.