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Unread 09-03-2019, 10:28 AM   #1
jchurch
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Kerdi/large format tile question

Hey folks,
First post, but I’ve been making use of this forum for the last ~2 months now. So far it’s gotten me through pouring a new mud pan, water proofing a 3x5 shower with the Kerdi system/Kerdi drain, and getting my shower floor tile laid down; thanks for all the great advice so far!

I’ve run into a question I haven’t been able to answers with prior posts...

I’ve used Versabond for the Kerdi install and floor tile (1.5” hex mosaic mats) with good success. My wall tile is going to be 6x24” wood-look porcelain.

By the directions on the bag, Custom recommends Versabond LFT (large format tile) for this application, using the rule that the longest edge of the tile is over 15”. However, I know the reason so many prior threads agree that Versabond is “OK as long as you’re alright with voiding the Schluter warranty” is that it’s LIGHTLY modified.

So my question is-will the Versabond LFT be too modified to use to lay tile over Kerdi? Is there an increased risk I’ll experience drying/cure issues? Assuming the “LFT” designation equates to more modifiers...anyone have experience with the combination of products?
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Unread 09-03-2019, 10:41 AM   #2
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Unscientific testing...

Also wanted to add-my 6x24 wall tile has the same surface area of a 12x12 tile, which IS acceptable to use with plain old Versabond per the rules on the bag.

Just to see the results, I took some scrap drywall and adhered one of my 6x24 porcelain tiles to it vertically while I was laying my floor tile yesterday...it hasn’t been quite 24 hours and I haven’t tried to pop it off yet, but it seems very well adhered. There’s no Kerdi in equation on this sample, just wanted to check and see if Versabond (non LFT) would work in a pinch...and it seems to.

Anyone have any insight on why the size limitation to use a large-format thinset is provides based on longest edge length rather than surface area?
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Unread 09-03-2019, 12:25 PM   #3
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Hi Jeff,

Either of the VersaBond products will work for walls, and both of them will void the Schluter warranty equally. I mix the thinset a little loose for walls, which probably voids Custom's warranty as well.
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Unread 09-03-2019, 12:49 PM   #4
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Thanks John; so all things considered, would one or the other (Versabond vs Versabond LFT) be “better”? LFT for better adhesion, or Versabond for better likelihood of fully curing in a reasonable time?

I think these are my best options, as I’m limited to what’s on the shelf at Home Depot...
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Unread 09-03-2019, 01:20 PM   #5
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Welcome, Jeff.

Not sure where you're getting the information that Versabond is "lightly modified" or that Versabond LFT "equates to more modifiers."

Both mortars meet the requirements of ANSI A118.4 and A118.11 when mixed with water, making them "modified" dry-set mortars. Both advertise a shear bond to porcelain tile of 200 psi. The primary difference is that the LFT (technically a LHT mortar) allows for application in much thicker sections than the regular Versabond. That usually indicates the inclusion of more course aggregates in the mortar, which you don't want at all for installing Kerdi or similar membranes and don't really need for installing your tiles if both the tiles and the substrate are sufficiently flat.

Why the industry (and in turn, Custom) uses the one-long-side in differentiating the "need" for a LHT (Large and Heavy Tile) mortar without regard to other factors is a mystery to me, too.

If I were in your position and had only Home Depot as a convenient source for my setting products, which is actually the case, I would most likely use Versabond for all the applications you have described. See my warranty information below.

If you think you somehow need a higher bond strength than the 200psi of versabond when the minimum required of the bond to the Kerdi membrane is only 50psi, you might try Custom's Flexbond available at Homer's. You could then achieve 400psi shear bond to porcelain tile while still bonding to a membrane required to demonstrate only 50psi shear bond to anything.

My opinion; worth price charged.
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Unread 09-03-2019, 01:42 PM   #6
jchurch
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Thanks CX, that clarifies matters a bit.

I’ll stick with the basic Versabond, as I’ve already got a couple bags in the garage for the work...never having hung larger tile, I was just second guessing myself since Custom makes the LHT specific stuff.

On the origins of my “lightly modified” comment...could’ve sworn I picked that up on an old post on here on the old “is Versabond ok for Kerdi” topic. But I’ve read quite a few over the last few months, so memory could be failing
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Unread 09-03-2019, 01:52 PM   #7
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No doubt in my mind that you picked up that "lightly modified" tag here on the site, Jeff and I've tried several times to get someone to tell me who originated it and what the "information" was based upon. All to no avail, of course. Rumors travel even faster on the ol' Intrawebs, eh?
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Unread 09-03-2019, 02:05 PM   #8
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Sure do! I can tell you with confidence I didn’t coin the term, since this is my first foray into tile setting.

I bought a tile saw back in April, intending to do a small accent wall in my master bathroom. The next week I realized the curb on the shower in that room had failed, which turned into a complete tearout/rebuild...in a not quite four year old house. I think getting the saw jinxed me.

Learned a valuable lesson on the contractor that built the original shower, and many more on the whole tiling process.
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Unread 09-03-2019, 02:15 PM   #9
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For walls, sometimes a non-sag thinset helps (Prolite). But, for years we used regular Versabond thinset for walls and floors. Actually, I can't really tell much difference from regular Versa bond from the LFT.
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Unread 09-03-2019, 03:50 PM   #10
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I can say, because I've been digging into it today, the "lightly modified" reference, or at least something similar that can be taken that way, appears in the Kerdi Shower Book .

There are discussion of the "Highly modified" thinsets and something like VersaBond being modified "but nor overly so" and therefore will set up in a sealed environment. That kind of thing. That may in fact be the source of your nomenclature problem .

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Unread 09-03-2019, 07:33 PM   #11
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As I understand it, there are at least four compounds, each with variations, in varying proportions along with the amount of cement, its type, and same for the aggregates (thus, LOTS of variations!), that can be used to create a modified thinset. A latex version needs to dry to achieve full strength. The others may not. The issue comes down to that IF the modifiers need to dry to achieve stability, while the cement will cure regardless and actually is stronger while kept damp during the curing process that modifieds help (as does a waterproof membrane behind a porcelain tile!), any induced movement prior to that level of stability can mean you break the crystals created while the cement cures, destroying its ability to actually create the interlocking bond. A large tile over a waterproof membrane does not dry out very fast...it can literally take months, starting from the edges in. Thinset shrinks slightly as it cures and dries out, creating a bit of stress, too. The modifiers, when mixed properly, literally coat the cement and act somewhat like a cushion, but it needs to be stabile which, at least with latex, doesn't happen until it dries.

FWIW, Schluter does make a modified that they will guarantee works, but other companies make some that will work fine, too. It's hard to know this on your own, and since Schluter doesn't have control over others, nor really want to be testing with all sorts of other thinsets, suggests those they know will work because either they make them, or worked with the manufacturer to set the 'formula'. One of the hassles is, test one today, and tomorrow they come out with a new, improved one, that may not, but keep the same name. Liability and reputation can each have consequences if something doesn't work at the end. Schluter is not alone on this, Laticrete will give you a much better warranty when you use certain of their materials, when you use their 'system' of components.
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Unread 09-04-2019, 07:31 AM   #12
jchurch
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Yes, throughout this whole process my life would’ve been way less stressful if I could have just used all Schluter material...but getting the thinset in particular was a non-starter, due to availability in my area.

I’ve more or less had to rely on the user feedback on this forum to get confidence in my material selections. At the rate I work anyway (typically only once a week, since I’ve still gotta go to work whilst gutting the shower) the tile will have plenty of time to dry before I grout it.
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Unread 09-04-2019, 07:40 AM   #13
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Using the VersaBond, Jeff, I wouldn't give the matter even a minute's consideration. Set your tiles, grout when you're ready (not before the minumum 24 hours, of course), and move on.

My opinion; worth price charged.
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Unread 09-04-2019, 08:51 AM   #14
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Will do! Thanks CX, and everyone else that weighed in. I really appreciate all the knowhow on this forum!
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Unread 09-04-2019, 12:03 PM   #15
jadnashua
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FWIW, in Europe, they use a different spec for their thinsets that can actually differentiate those that will work well with waterproof membranes. In Europe, to keep all of the Eurozone countries happy, they do specify a modified, but it must be with a certain spec. The ANSI spec we use in the US does not differentiate that feature, so, since a good unmodified also works, Schluter chose to select that method since they could get a national approval rather than having to deal with numerous countries in the Eurozone. This goes against the grain of many tile setters that had been schooled about why one needs modified thinsets. THinsets are a 1950's invention (Laticrete). There are tile installations that sometimes included glass which may be even harder to bond than porcelain, that have been intact for centuries using older techniques and less controlled processes, so things could vary from batch to batch. They worked when done right. Do your tiling over Kerdi or Ditra, it would work right, too with an unmodified. There's a bit more margin for error with a modern modified, and some have the mindset it's required. Not every situation is clear cut, so that margin for error gives a piece of mind that, if not done well, may still fail. Keep in mind, the chain is only as strong as the weakest link, and the fleece of a bonded waterproofing membrane is only required to exceed 50psi shear. The bond to the tile will be much stronger than that with an unmodified. A good unmodified's bond could exceed that of a cheap modified.
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