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Unread 02-08-2020, 01:45 PM   #46
ss3964spd
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And some thinset mortars contain more modifiers than others, Custom's Versabond and Flexbond are examples - VB being less modified.

I had to remove a 12X24 porcelain floor tile that had been set, but not grouted, for about a week and the VB appeared to be completely cured.
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Unread 02-09-2020, 05:21 AM   #47
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... so getting a little confused here but mostly due to my ignorance.

If DITRA recommends using a "non-modified" for setting tile then doesn't that exclude VB LFT, since it is a modified thin-set?

The install doc says ANSI A118.1 not A118.11 for tile setting?? It seems based on that the VB LFT would only be useful for laying the DITRA to the plywood floor and that would be an expensive endeavor at $30 a bag. Is that so Schuler can cover their ass in case of failure since those in field are using VB LFT and I assume other modified thin-set to set tile and having success?


Trowel sizes:???
Setting DITRA - 1/4 x 3/16 v-notch
Setting tile - 1/2
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Unread 02-09-2020, 09:03 AM   #48
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I don't understand Schluter's recommendation for using a non modified mortar, aside from wanting to ensure a full and complete and expedient cure, and thus a faster install. Maybe some of the pro's here can elaborate.

But since the top of Ditra is nothing more than smooth plastic no mortar, modified or not, will actually bond to it. The mortar is mechanically locked in place by the shape/ridges of the waffles. See pic below.

I used Ditra Heat on my floor. While it is different than regular Ditra in appearance it is made of the same material and the principle is the same; the mortar is locked in by the shape only.

My first hand, and quite novice, experience using Versabond on top of Ditra and under 12X24 porcelain tile conclusively proves that it will cure just fine.

Use their recommended trowel size for setting the Ditra to the plywood. If your floor is very, very flat, and your tiles are too, you can try a 3/8" slant notch trowel to set your big tiles, as I did, or just go with the regularly recommended 1/2" square notch trowel.
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Unread 02-09-2020, 09:30 AM   #49
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VB, my advice was not following Schluter's recommendations. The thinset curing faster means nothing to me if the tiles aren't bonded well. I go off of past experience and like most here, have seen many jobs where the tiles popped right off the floor leaving the thinset behind. Versabond sticks real well for only being lightly modified. But, yes, it is still modified.
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Unread 02-09-2020, 09:38 AM   #50
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VB, I haven't posted this photo for a while, so I'll dust it off and post it here. It shows a 12x12" porcelain tile, having been set with a non-modified thinset mortar (Laticrete 317 as I recall), being removed from Ditra over drywall in a test lab situation. Clearly the unmodified mortar will bond adequately to the porcelain tile.

Name:  Removing Tile From Ditra.jpg
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And keep in mind that the tile industry's minimum requirement for bonding the Ditra, or similar membranes, is only 50psi, so anything above that strength in bonding the membrane to the tile is not of much consequence to my thinking.

That said, I find very few unmodified thinset mortars as easy to work with as a modified mortar. One of the easiest is DitraSet, which I personally doubt is actually not modified, but that's a different discussion.

And I know from many tests and actual installations that Custom's VersaBond and a few other modified mortars will work just fine in airless situations that Schluter finds so fearful, and I don't (didn't) hesitate to use such mortars with Schluter products when installing tile for hire.

My opinion; worth price charged.
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Unread 02-10-2020, 02:22 PM   #51
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CX, that definitely looks stuck to me... I think I'm fine with VB after this discussion.

VersaBond (white) for DITRA- https://www.homedepot.com/p/Custom-B...SW50/100091767

VersaBond LFT for Tile - https://www.homedepot.com/p/Custom-B...MM50/100154560

Since the DITRA looks like it will take a little more thin-set to fill the gaps how much extra should I calculate per square foot? I think a 50lb bag is good for 100 square ft??
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Unread 02-11-2020, 08:18 AM   #52
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I think a 50 pound bag will be more than sufficient. The waffles in Ditra aren't very deep.

Do you plan to pre-fill the Ditra, let it cure, and then tile, or just fill and tile in one step? Either way, take care to fill the waffles completely, they tend to trap air.
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Unread 02-11-2020, 09:18 AM   #53
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Fill and tile in one step is the plan...

Based on Custom's website a 50lb bag should cover appx. 50sq ft and your good with that even after filling the DITRA? Just trying to estimate materials..

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Unread 02-11-2020, 09:24 AM   #54
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My bad, VB, I was thinking only about filling the Ditra, not filling and setting tile.
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Unread 02-12-2020, 05:53 AM   #55
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Was just reading another thread ("I think I got the wrong plywood" https://www.johnbridge.com/vbulletin...79&postcount=6) on the forum and was curious why you wouldn't want the top layer attached firmly to the structure?

It seems to me that you would want your base as structurally sound as possible.

VB,
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Unread 02-12-2020, 09:44 AM   #56
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You would, indeed, "want your base as structurally sound as possible," VB. And you do want your top layer of subflooring "attached firmly to the structure," just not directly to the joist structure.

There has been testing done within the tile industry showing that there can be some isolation of the second layer from movement in the joist structure by fastening the second layer only to the first layer of subflooring. Fastening it very soundly to the first layer. The industry doesn't recommend gluing the second layer to the first (which I would do) and that is, I've been told, because of a fear that the gluing would not be done correctly. I find that a bit specious, personally, as there are also a number of other things in the construction of a wood framed subfloor that could be done incorrectly.

But if the avoidance of driving fasteners through the second layer of subflooring into the joist structure is in any way helpful, I'm quite content to do that and to recommend that our visitors do that. It's also easier to install the second layer that way.

Here is a good article from our Liberry on what I think is the best way to install that second layer of subflooring (which they erroneously call underlayment) in almost all cases. One of the authors of that article has told me that with their closer fastener schedule they can achieve "very close" to the same structure as with full coverage gluing.

My opinion; worth price charged.
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Unread 02-12-2020, 03:14 PM   #57
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OK, yes that makes sense... I thought I was missing something.

Thanks.

VB,

p.s. any thoughts on the additional thin-set needed for filling the DITRA, I'm assuming it's minimal???
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Unread 02-12-2020, 05:31 PM   #58
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Compared to just tiling over a flat surface, tiling over something like Ditra or a similar membrane, does use moderately more thinset. What kind of coverage you'll get depends on the trowel you use and the membrane.

Have you read the Ditra Installation Manual?
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Unread 02-13-2020, 06:39 AM   #59
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I have read the manual but there is no indication of coverage or material usage.

I'll be using a 1/2" trowel but that would really not impact the amount of thinset needed to "cover" the DITRA???

Here is a note about attaching the underlayment.. they are saying, to not secure the underlayment to the structure but only the subfloor.

Name:  SNAG-0361.jpg
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"The following guidelines must be followed when fastening underlayment panels:
1. Use ring shank nails (no staples) or wood screws (no drywall screws).
2. Fasteners must pass through entire thickness of underlayment and subfloor panels with minimal penetration into joists (see figure 2)."
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Unread 02-13-2020, 09:14 AM   #60
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See post 56, VB. That excerpt is from the same article I linked. One of the co-authors worked for Schluter at the time of its publication.
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