bridging plywood subfloor to concrete sub [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-16-2010, 04:43 AM
I have a gap between my plywood sub floor and my concrete subfloor. How does one bridge these and prevent new tile/grout from cracking?

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02-16-2010, 05:54 AM
You don't. You need to leave an expansion joint over the plywood/concrete joint.

Jim wood
02-16-2010, 07:50 AM
I would try to lay out the tile so to have a grout joint there and fill it with grout caulk.

02-19-2010, 09:19 PM
any further elaborations on expansion joints?

would you recommend Ditra over both surfaces? And, if so would this also decrease the possibility of cracking,etc?

The Kid
02-19-2010, 09:57 PM
to the ditra question:

No and No

02-20-2010, 07:00 AM
can I have a rationale to "No Ditra". Are from the camp that you dislike Ditra?

I'm bonding directly to plywood? Doesn't sound right. Hardbacker? or Cement board?

02-20-2010, 07:30 AM
Ditra is a good choice over plywood or concrete, but Ditra cannot be used to bridge between the two to prevent cracking of your tile over the joint. The joint must be treated as an expansion joint and continued to the finished surface. Schluter will not warranty or endorse using Ditra to bridge the gap.

With that being said, I personally know of a contractor that did use Ditra to do exactly what you are asking of it and was successful. It would be very risky to do this and I don't suggest it.

Dave Taylor
02-20-2010, 07:39 AM
craka wrote: can I have a rationale to "No Ditra".
Plywood and a cement slab are wildly different substrates that move (expand/shrink) so wildly differently they need to be tiled separately...... that is...... separated by an expansion joint like Jim and Bob advise above.

Hardbacker? or Cement board?

No and no.

Hope this helps.


Wow that Tracy is quick this AM.
What he says goes for me too.

Jim wood
02-20-2010, 07:52 AM
Just to clarify you could use Ditra on the plywood and on the concrete as long as the Ditra is CUT at the joint and then a break in the tile at that point with a soft joint.
I hope this helps.

The Kid
02-20-2010, 12:12 PM
I am not knocking ditra in any way, I just wouldnt bridge that gap with it.

This is how I would treat it:

02-20-2010, 06:12 PM
thanks everyone for your posts