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Unread 04-06-2020, 09:45 AM   #1
Danroonie
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Air free thinset advice

Putting in a small curbless shower - the floor outside the shower floor currently has ditra uncoupling membrane but it was not raised enough. See diagram. With the tile suppliers closed in my area because of coronavirus I was fortunate to get goboard to raise it to the right level. The goboard instructions say to use either unmodified or modified thinset (ANSI A118.1 A118.4 standard) See diagram.

Since air cannot dry the thinset - I assume unmodified thinset is the way to go. Ditra and Goboard product sheets approve unmodified thinset. Since it's a floor - I don't have to worry about sagging - so I'm good to go with any cheap unmodified (ANSI A118.1) mortar.

For the 24" x 12" tiles on the goboard- I was also going with all-set no-sag for the walls and cheap unmodified thinset for the floor.

Does that make sense?

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Unread 04-06-2020, 10:15 AM   #2
John Bridge
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Hi Dan,

Un-modified thinset will work but not "cheap" thinset of any sort. Pay for the best.

Also, I wonder if things might work out better if you pull up the Ditra and then install the GoBoard? I'm thinking height-wise. I don't know what the actual difference in height is.
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Unread 04-06-2020, 01:19 PM   #3
Danroonie
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Honored to have your reply!

This one says it meets ANSI A118.1 so I guess it's unmodified. ProLite Tile and Stone. On the HD website it's relatively expensive and well regarded - can be for LFT - can be used in medium bed applications - so I guess it's good - below the Goboard and LFT. Without starting a holy war I need something I can pick up quick at an open store like HD or Lowes- is that one a good bet?

I don't want to rip the Ditra that's there since it's the right height and leveled etc.

BTW there's 1 1/4" subfloor screwed and glued to 2x12's so pretty stable.

ps. the disabled enabled curbless shower will come in handy for self-sufficient showering during these covid times.
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Unread 04-07-2020, 10:39 AM   #4
John Bridge
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Dan,

You can do a little test with any thinset. Bond a couple pieces of tile together and sink them in a bucket of water for a day or two. If they remain stuck together you're good.

My go-to mud for Kerdi and Ditra was most probably VersaBond from Home Depot. It's modified but it worked for me hundreds of times.
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Unread 04-07-2020, 04:15 PM   #5
Danroonie
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>Bond a couple pieces of tile together and sink them in a bucket of water for a day or two

Thanks again! Perfect - not sure how long to soak - but in my layman's words here's what I heard- it's worth double- checking since this will take days - though it's worth doing the job right!
1. Day 1: Get VersaBond-LFT Medium bed Mortar from HD.
2. Cut (4) x 8" pieces off the 24" LFT (that's 33% ish)
3. Mortar two sets together.
4. Wait 24 hrs
5. Day 2: Plunge one set in a water-filled bucket
6. Day 3: Pry the first set from the bucket apart. If they don't pry - the curing time worked- Finished otherwise 24 hr test failed.
7. Day 3: If step 6 failed take the 2nd set that's been curing 48 hrs and plunge in the bucket
8. Day 4: Remove the second 48hr cured set from the bucket. Try to pry apart. If they don't pry - the curing time worked- Finished successful. Otherwise 48hr test failed. Take a stiff drink, grab a quality unmodified mortar and repeat from step one.

Does that sound about right?
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Unread 04-07-2020, 07:26 PM   #6
jadnashua
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To achieve full strength, you need the chemical reaction of the curing process for cement. In the industry, that's assumed to be after 28-days, but it does continue to get stronger for years afterwards, but at a MUCH slower rate. A lot happens in the first 24-hours. THen, if it's a modified thinset, the modifier must also reach it's proper condition. The original modifier and still used by some companies, was a latex based product. That modifier DOES need to dry, and can soften if it is submerged, or not allowed to dry. Many, not all, of the other modifiers used can achieve stability without drying. It just depends on what the modifier is in the product you use.

Schluter did a test with a latex modified mortar (actually a glass plate) over Ditra and found that the mortar didn't dry out in the middle for nearly three months. Until that time, it wasn't fully stable. Grout the edges, and it would take even longer. And, latex tends to re-emulsify if it gets submerged. You may see a statement on the spec sheet that the product is or is not suitable for pools or other places that may be submerged. Cement holds together because when it cures, it grows crystalline spikes that interlock sort of like Velcro. Unlike Velcro, they're rigid, thin, and can fracture. THey won't if they aren't flexed too far, and can make a very strong bond. Different configurations of cement grow different size and shape crystals, so can be customized for the application.

When mixed properly, the modifier acts like a cushion around the cement spiked crystals, protecting them somewhat and providing a little more flexibility and water resistance (as long as they don't re-emulsify).

The US spec for thinsets doesn't include info about stability or whether it needs to dry first. The Euro spec does, but since cement is heavy, that made here usually isn't tested to the Euro specs, so we don't really know. The maker does, and might tell you if you call, but it's not defined by the ANSI spec we use.

Makers don't change their formulations that often, so people have found products that worked. Beware if you rely on that and then find a product labeled, new, improved...it may not still work as others have reported. That's the main reason why Schluter won't recommend a product they don't have control over. They know what US spec will work both under and over their membranes. They do sell modified thinsets they will guarantee work with their membranes. Some other companies have done their testing and will offer an alternate warranty. The safest is to use products from the same manufacturer, but that doesn't mean others won't work.
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Unread 04-07-2020, 09:40 PM   #7
Danroonie
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I can get All-Set on top of ditra as that is recommended by Schluter.

Do others think that is the best approach?

After I'm done setting the GoBoard I'll be looking for a product that pros have found success with large format tile on backer board like goboard.
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Unread 04-10-2020, 10:00 AM   #8
Brennanleroy
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John,
When we were at Schluter for a workshop 6-7 years ago, I remember the instructor telling us that Ardex X5 was acceptable over Ditra, due to its chemical ability to dry. I recently inquired with the Schluter Customer Service and was told that setting over Ditra with Modified thinset would not be warrantied. Unless of course, it was the Schluter modified thinset.
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