Ditra Seams and Plywood Seams [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-28-2008, 06:02 PM
Is there any recommendation on alignment of ditra seams with plywood seams? I've read the ditra installation manual, and can't find one (but may be overlooking it). Here's the situation I'm concerned about:

I have a relatively small room 10x6 (foyer) with a closet. The original subfloor was dimensional plank flooring. I've overlayed it with 1/2 plywood per the installation manual screwed 4" on edge 6" in field. I was able to meet the requirements of not ending on a joist for the main room but the closet is another story.

There is a joist (but no plank seems) right under the closet entry. The main room plywood subfloor goes right up to the closet entry and then the closet subfloor plywood was notched (3.5") so that it overlays the entry with the proper 1/8" spacing betewen planks. I thought of notching the plywood further into the main floor to get it further away from the joist but thought that may actually cause more problems given that is where the real foot traffic will be. So my basic questions...

1) Are there any rules about overlap requirements for ditra and subflor seams (waterproofing is not an issue in this case)

2) If not is it ok to overlay these seems, or could I notch the ditra in reverse (3.5" from foyer into closet) so it overlaps a few inches from the entryway?

I was going to lay the ditra lengthwise along the longest wall but could also go the other way (parallel to the main floor joints) and have one sheet go completely into the closet.

3) This is my first Ditra install (if you haven't guessed). I know that the modified thinset under the ditra should be mixed to a pourable consistancy (wetter than normal). What about the unmodified between the tile and thinset? I'm thinking it should be mixed wetter to ensure that the tinset completely fills the waffles.

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Brad Denny
01-28-2008, 06:41 PM
Hi Scott,
If my training serves me, no worries about the Ditra seams. One of the beauties of the system is the ability to piece all scraps in with no waste. You are correct about the consistency being wetter for applying it to the subfloor, but you still want the mortar to hold a notch. As for above, flat troweling in all directions should fill the waffles well, you need the thinset on top to support the weight of the tile (not real runny). I assume you ran your joists through the Deflecto?

01-28-2008, 07:39 PM
Hi Scott, I always lay the Ditra out so that it is atleast 3" to 4" away from any seams. I have this thing about wasting Ditra too, I waste like none. Well ok, just a little.

01-28-2008, 08:04 PM
Your number 2 is what I would do:

notch the ditra in reverse (3.5" from foyer into closet) so it overlaps a few inches from the entryway?

01-28-2008, 09:23 PM

I appreciate your quick replies, they were exteremly helpful. I have few more screws to put in the plywood this evening and with the replies can actually cut my Ditra to thinset tomorrow night. I can see why you guys don't want to waste Ditra. Schulter must be making a mint off the stuff. The price didn't sound to bad until I was at the checkout line.

I'll keep the thinset mix "normal" between the tile and ditra. I did run deflecto and I'm go for cermaic tile (which is good). Reading this board made me completey change my original plans. I was originally going to go CBU over dimensional lumber which I found out could cause the end of all life as we know it (unfortunately the tiler that did my kitchen did it that way).

To be on the safe side I think I'll takes Steve's and Musky's tips on the seems. I'll lay the Ditra out the shorter way so that I can notch it in the doorway, that should give me 3-4".

I don't know if its ok for this question in this thread. But do you guys practice your layout on the Ditra or do you usually do that on the plywood before putting the ditra down.


01-28-2008, 10:43 PM
Hi Scott, I assume your talking about the tile. I usually check it before I do anything depending on the room. But that doesn't mean you can't check it after the Ditra is in.

01-29-2008, 08:54 AM
Thanks Mike, thats what I needed to know.