Replies

1. 
   MojoMan | Dec 06, 2003 05:19am | #1

   High prices, or not, I don't think this is a good time to skimp on the plywood. I would use as much thickness of plywood as needed to get the height you need. Skip the backerboard. Glue and screw the plywood (AC or underlayment). Hit the joists with the screws, not just the subfloor. The goal is to make the floor as stiff and stable as possible so the tile doesn't crack. I suspect backerboard does not contribute as much as plywood to this kind of structural strength.

   Al Mollitor, Sharon MA

1. 
   WebTrooper | Dec 06, 2003 06:51am | #2

   I would do exactly as MojoMan said.~ WebTrooper ~

   "But dont take my word for it. I was wrong once and it could happen again!"

2. 
   CAGIV | Dec 06, 2003 11:03am | #3

   I'd not tile directly to the ply your just asking for problems when the wood expands and contracts and the thinset pops its bond.

   The CBU's won't add much in stiffness so build up as much as possible with ply, NOT osb and then lay 1/4" CBU on top of that The ply gets nailed or screwed to the joist, the CBU does not.  Avoid the joists when laying the CBU's you can make fast work of it with a roofing nailer and thinset.

   Offset the joints between the two layers of ply and offset the joints in the CBU's from the top layer of ply.

   oh and rip the vinyl out first you can ask Jeff Buck why when he comes along shortly ;

   Jeff or Boris will give you some of the best answers here.

   Just curious cab's in or out at this point?

3. 
   EricPaulson | Dec 06, 2003 05:38pm | #4

   I'm with Mojo.

   Ply 5/8 or 3/4 glued (yellow tite bond or similiar) and screwed. I put around 100 screws per sheet. Used to drive the helpers nuts till I got the quick drive!

   Use good ply, glue and LOTS of screws and hit the joists! Oh did I mention lots of screws? I believe that most of the movement that may be experienced with ply is due to poor fastening. Kept dry, it simply is not going to expand and contract enough to dislodge a well set tile.

   With all due respect to others knowledge and preferences, I have NEVER had a problem with ply. Todays modified thinsets are really wonderful products to work with. As hard as they are they also retain a degree of flexibility. Make sure the ply is VERY clean before starting. I sweep, vacuum and sometimes damp mop to get rid of that dusty film that is often present.

   I just did a job with Mapei Kerabond Thinset mixed with Keralastic Additive. It reminded me of the old three part epoxy systems we used to use back in the 70's and 80's. This stuff is like a rock!

   It has always been a running joke to think about having to come back and remove this whole system someday for a reno!

   Eric