Replies

1. 
   MJLonigro | Feb 18, 2005 11:45pm | #1

   I think by better they mean B-C or A-C....

   What is this plywood for???

   
   

   ---

   Edited 2/18/2005 3:49 pm ET by MJLONIGRO

1. 
   Toolsguy | Feb 18, 2005 11:52pm | #2

   I'll be putting down ply to add strength to a sub-floor and then tiling onto it.

1. 
   MJLonigro | Feb 18, 2005 11:55pm | #3

   CDX is fine for that...just make sure you buy 5 ply CDX...most lumber yards around us only sell 5 ply....HD sells 3 ply cheap...but they do sometimes have 5 ply...

1. 
   Toolsguy | Feb 19, 2005 12:00am | #5

   Thanks. I rarely buy any lumber from HD. Learning the hard way that their stuff is sub-par.

1. 
   artman | Feb 19, 2005 12:36am | #6

   Here in northern Michigan there stuff seems superior to most others."The purpose of life is rapture. Here and now"

2. 
   jackplane | Feb 18, 2005 11:57pm | #4

    Since you're adding strength to a subfloor and not building new, CDX is fine.

2. 
   blue_eyed_devil | Feb 19, 2005 12:43am | #7

   Toolsguy, the last letter X indicates that it has exterior glue and will hold up under exterior conditions. The letters C and D indicate the finish of the sides. C is the better side. D is rougher than C.

   Since you're using this as an underlayment, the strength generated by more plys is not really a factor. The 3ply stuff will suffice, since it will be supporte by the underlying plywood anyways.

   When you lay the cheaper plys, make sure you space it on all four sides.

   blue

   Just because you can, doesn't mean you should!

   Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!

3. 
   JeffBuck | Feb 19, 2005 12:48am | #8

   as an aside ...

   U gonna lay backer board down on top of the ply ...

   then tile over that?

    

   Jeff

     Buck Construction 

      Artistry in Carpentry

           Pgh, PA

1. 
   blue_eyed_devil | Feb 19, 2005 01:22am | #9

   Jeff,  I was curious about why he'd belaying cdx if theres already a subfloor.

   I'd be laying a mud bed. If it was vinyl tile, I'd be laying 1/4" luan underlayment.

   blueJust because you can, doesn't mean you should!

   Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!

2. 
   Toolsguy | Feb 19, 2005 02:58am | #10

   Laying down the extra layer of ply to bring the tile level to the adjacent room's hardwood floors.

   No backer board. Tiling onto ply. Need to strengthen the sub-floor with another layer of ply. The backer board stuff doesnt add to structure, just makes for a good adhesion surface. Taking the advice of a pro who does it that way.

   L

1. 
   Shep | Feb 19, 2005 04:00am | #11

   a friendly warning-

   most tile mfgs. recommend installing tile over a cement backer board. Ply is pretty stable, but backer board doesn't move.

   Personally, I wouldn't set tile on anything else than cement board. If you need to stiffen the floor, add a layer of 3/8 or 1/2 " ply before the backer.

1. 
   Toolsguy | Feb 19, 2005 04:33am | #12

   Thanks for the info but I cant afford the height to add both products.

   ps - mapai thinset is a premium thinset and recommends use onto ply. also, I'm following instructions from two very reliable pros. (Minority opinion about ply but they are extremely reputable nonetheless)

1. 
   blue_eyed_devil | Feb 19, 2005 06:41am | #13

   Hmmmmmm?!

   blueJust because you can, doesn't mean you should!

   Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!

2. 
   Toolsguy | Feb 19, 2005 07:09am | #14

   Not sure what you mean but i'm following the advice of some trusted folks. What else can I say.

    

3. 
   blue_eyed_devil | Feb 19, 2005 07:33am | #15

   How about following the advice of the tile manufacturers and their associations.

   I simply wouldn't trust tile that was set on wood. I've only seen it done once. The people couldn't keep the grout in the joints.

   blueJust because you can, doesn't mean you should!

   Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!

4. 
   billyg | Feb 19, 2005 02:30pm | #16

   Blue is right.  Don't tile directly to plywood.  Use cement backerboard or a membrane.

   Also, do NOT use CDX for a subfloor under tile.  The "D" means that it has unfilled knotholes, which is not good under tile.

   The Tile Council of America does not recommend using CDX under tile.  For gawds sake, it is a sheathing material, not a subfloor!

   See below for more.

   Billy

   http://johnbridge.com/vbulletin/showthread.php?t=8921

   Dave Gobis da Man! Join Date: May 2001 Location: Clemson, SC Posts: 1,284

   Not using CDX is a wood industry recommendation, agreed to, shared, and published by TCA. CDX is not a rated floor panel and will not acheive the deflection rating required for 24" centers. 3/4" CC Plugged, minimum. I can't in my wildest dreams imagine a repair to be effective. As for the injection bonding being common, that is a sorry statement in itself. I have done it, with latex, and I would say it might have a remote chance, but not in this installation. I suspect the tile is grouted tight to the wall or base too adding additional shear force to the already excessive deflection. __________________ Dave Gobis, Exec. Dir. Ceramic Tile Education Foundation http://www.tileschool.org

   View Image View Image

1. 
   Toolsguy | Feb 19, 2005 03:39pm | #17

   Man! Just when I think I have it squared away in my head  that i'm going in the right direction.

   Let me pose this question then. I believe my sub-floor might only be 5/8" thick. If this is the case then, from what I've been told, thats not enough of a foundation for tile and adding CBU or backerboard wont add to the strength of the floor. Hence the need for adding ply to the sub-floor.

   I cant add ply and CBU because it will raise the height too much.

   Any recommendations?

1. 
   jrnbj | Feb 20, 2005 09:45am | #18

   1/2 inch ply + 1/4 CBU, done.....

2. 
   blue_eyed_devil | Feb 20, 2005 03:05pm | #19

   How have you determined that the subfloor isn't strong enough? I'm skeptical. I think 5/8" subfloor is plenty strong enough.  Of course, I'm a mudbase kinda guy. In a previous house I owned I layed a dry pack 3/4" mud base over 5/8" subfloor and ten years later the tile still looks great...no problems anywhere. I was just there last night.

   blueJust because you can, doesn't mean you should!

   Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!

1. 
   Toolsguy | Feb 20, 2005 03:50pm | #20

   I was told I needed at least a 3/4" ply base to start on.

   question: when you say "mud" base, do you mean the kind you poured? Those are stronger than the CBU layed kind no?

   Edited 2/20/2005 7:51 am ET by Toolsguy

1. 
   blue_eyed_devil | Feb 20, 2005 04:46pm | #21

   I think its a lot stronger. It's a fairly easy process....tar paper, mesh, mix in the "drypak". The dry pack is a mixture of cement and sand with as little moisture as possible. I lay 3/4" screeds and spread it over the floor using concrete steel (magnesium actually) float. I've only used cement board on two different applications and I don't think that there is too much time differential.

   In most instances, I think I'd do the mud base.

   blue Just because you can, doesn't mean you should!

   Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!

5. 
   McFish | Feb 21, 2005 09:50am | #22

     Every professional tilesetter that I know lays floor tile over cbu or a mud bed.  That is what I always tell folks when the question arises, and it comes up a lot.  Pros tend to be conservative and do things a certain way because it works, and they dont have to come back and fix it.   I've seen tile laid over all kinds of surfaces though and sometimes it works, sometimes it doesnt.  My own brother ignored my advice and laid tile over cdx ply in his BATHROOM!.  If your willing to risk having to do it over again then well...  (note proper use of elipsis)   But why not do it right the first time.   I think you may be able to use marine ply, which is more expensive but is void free.  cdx has voids and is not a good choice for your application. 

                                                                                                     Tom

1. 
   Toolsguy | Feb 21, 2005 03:44pm | #23

   Yep, I've been  re-evaluating. I think I'll use CBU. The ply might work for the guys I've been talking to but maybe they have it down to a science.

   Also seems like I'll be able to match the height  better with 1/4" CBU.