CDX plywood substrate [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


View Full Version : CDX plywood substrate

11-18-2009, 10:59 AM
I'm looking at a repair job. Concrete tiles laid down over CDX plywood (don't know the thickness). They reinforced a beam under the floor and now the tiles are popping. They're practically floating all over the floor because the thinset is nothing but dust - no adhesion. The proper thing to do would be to rip up the entire floor and start again. The client would be happy to just plop down some new tiles, understanding that the install might not last. CDX is not exterior grade, correct? If I do this what should I use as adhesive? Flexbond? or is there a mastic that would be stronger? I appreciate any response...


Sponsored Links

11-18-2009, 11:19 AM
Hi Libby,

CDX is a sheathing grade and not suitable for use as any part of the subfloor/underlayment. Best thing to do would be to remove that CDX and start over.

Tool Guy - Kg
11-19-2009, 01:21 AM
The "X" in "CDX" stands for exterior rated glue. So it is exterior rated, but like Joe said, it's not suitable for tile and may need to be removed.

We need more info to help give you more detailed help. When you said the beam underneath was "reinforced", do you mean it was jacked up and this caused the tiles to pop? Or were the tiles popping prior to the beam work? Can you investigate and report back to us with all the layers that make up the floor? Start with the subfloor that's directly fastened to the joists and work upward...please note their thicknesses as well. If you need a place to examine a cross section of the floor, see if there's an HVAC vent cover than can be removed to give you a good view. :)

Houston Remodeler
11-19-2009, 01:43 AM
The C & D in CDX stand for wood grades C and D which are below A = cabinet grade, then down hill from there. The C is on one face and the D is on the other. CDX is exterior grade sheathing, also used for roof building. It often has interior voids in it. The glue may be exterior rated, but the grade of lumber is not able to take much, if any moisture.

If there is no HVAC opening, how about a pipe penetration?

11-19-2009, 12:45 PM
Thanks so to all for affirming my fears. Yes, the floor joist was jacked up, but the other culprit is still the use of CDX. The tiles began popping after the reinforcement. But there is absolutely no thinset left on the wood. I agree, it needs to be redone. My ultimate question, though, is what adhesive to use if they are only willing to do the shoddy, cheap repair of replacing the tiles on the CDX?

Thanks again-I'll be meeting with them tomorrow so I can look at the layers of subfloor then.


11-19-2009, 01:02 PM
If you can't convince them to replace the plywood, at least talk them into adding backerboard. This will bridge any knotholes visible on the surface, and just may prevent any buried voids from showing through.