Which thin set to use??

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Duffer

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I have schulter sloped pan on the floor of my new shower.
The walls are coated with Mapei Aquadefense.
Where the pan and wall meet at the bottom I want to seal the joint with a folded kerdi band.

My question is regarding the thinset mortar to use that will not fail.
The band to the pan calls for unmodified Thinset ( ( schulter)
Mapei specifies modified thinset to be used when installing tile and stone to Aquadefense but nothing in the literature mentions the use a product like kerdi.

I was thinking of using unmodified as will have if mixed to install the kerdi membrane on the pan.
Then I would seal the seam of the band along the wall with silicon and coat it with Aquadefense.

Comments welcomed.
 

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Jadnashua

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FWIW, when you mix waterproofing systems, you essentially have no warranty from any of the companies involved. That doesn't mean that it won't work.

You MUST put Kerdi on the foam pan, otherwise, you'll lose a LOT of the ultimate compressive strength, and would then call for unmodified to both install the membrane and the tile to it. Do NOT just put the liquid waterproofing on the pan.

The Kerdi fabric's seam waterproofing relies on there being fleece on the overlaps of both sheets...you won't have that with AquaDefense on the wall. The small fibers from both sheets in intimate contact with the spaces filled with the thinset break up capillary action, creating the waterproofing.

What may work is to install the Kerdiband, and AFTER the thinset has cured, add some AquaDefense from above the edge onto the Kerdiband.

While a modified thinset will bond Kerdi (in reality, thinset, neither modified or unmodified, technically 'sticks' to Kerdi...it surrounds the fleece, and when cured, locks it in place), the issue is that latex modified (one of several ways to make a modified) requires drying in addition to the cement curing, and that's really hard to do between a typical porcelain tile and a waterproof membrane. Depending on the size of the tile, it can literally take months, and the thinset won't have the design characteristics until that modifier has a chance to dry...the cement will cure in a known, fixed time.

You're in uncharted territory when you mix systems, and technically, the plumbing code certification no longer applies. I doubt an inspector will ding the install, but technically, he could.

You might want to check out www.johnbridge.com . That site specializes exclusively on tiling, and showers are a big portion of that, along with walls, floors, counters, etc.
 

Duffer

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FWIW, when you mix waterproofing systems, you essentially have no warranty from any of the companies involved. That doesn't mean that it won't work.

You MUST put Kerdi on the foam pan, otherwise, you'll lose a LOT of the ultimate compressive strength, and would then call for unmodified to both install the membrane and the tile to it. Do NOT just put the liquid waterproofing on the pan.

The Kerdi fabric's seam waterproofing relies on there being fleece on the overlaps of both sheets...you won't have that with AquaDefense on the wall. The small fibers from both sheets in intimate contact with the spaces filled with the thinset break up capillary action, creating the waterproofing.

What may work is to install the Kerdiband, and AFTER the thinset has cured, add some AquaDefense from above the edge onto the Kerdiband.

While a modified thinset will bond Kerdi (in reality, thinset, neither modified or unmodified, technically 'sticks' to Kerdi...it surrounds the fleece, and when cured, locks it in place), the issue is that latex modified (one of several ways to make a modified) requires drying in addition to the cement curing, and that's really hard to do between a typical porcelain tile and a waterproof membrane. Depending on the size of the tile, it can literally take months, and the thinset won't have the design characteristics until that modifier has a chance to dry...the cement will cure in a known, fixed time.

You're in uncharted territory when you mix systems, and technically, the plumbing code certification no longer applies. I doubt an inspector will ding the install, but technically, he could.

You might want to check out www.johnbridge.com . That site specializes exclusively on tiling, and showers are a big portion of that, along with walls, floors, counters, etc.
Thanks for the advice. i have a much better idea now on how to proceed.
I will "install the Kerdiband, and AFTER the thinset has cured, add some AquaDefense from above the edge onto the Kerdiband."

One more question.
When I place the Schluter pan on my concrete floor I will be using the unmodified thinset as shown on the Schluter videos.
Is there a need for me to add some adhesive to the current concrete to ensure there is a bond between the thinset and the concrete?

Thanks in advance
 

Jadnashua

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One more question.
When I place the Schluter pan on my concrete floor I will be using the unmodified thinset as shown on the Schluter videos.
Is there a need for me to add some adhesive to the current concrete to ensure there is a bond between the thinset and the concrete?

Thanks in advance
The thinset there is more to ensure that the pan is fully supported than to actually hold it to the concrete slab. If you sprinkle some water on the slab, if the water gets absorbed, it will bond very well with the unmodified. In fact, if it beads up, neither a modified nor unmodified will bond (that typically means they used a sealer on the slab).

Make sure that the slab is flat AND level...don't try to fix it by thinset and setting the pan. Once you set it in place, perform a shuffle dance across the entire thing, and make sure you've used the proper trowel notch size. Once down, it's there for the duration!

I will caution you about the PVC cement and cleaner - spill some on the foam, and it will eat a hole. So, be careful when installing the drain. Not catastrophic, but could be if you spilled the whole can! Avoid kneeling or walking on the pan directly until you have it covered with tile...use a piece of plywood, or maybe some scrap drywall or you'll end up with divots. Again, not catastrophic, but could be a (minor) issue.

Once covered and cured at least overnight, the foam will provide at least 500psi compressive strength. Prior to that, quite a bit less. I wouldn't walk in there in high heels, but bare feet or normal shoes, once tiled, you will not damage anything. A deckmud pan once cured, would have about 4000psi compressive strength for comparison. Cement is a lot denser than foam! They use foam underneath highway approaches to bridges...done right, it works just fine.
 

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Thanks so much for the advice, especially the "heads up" on the PVC cement and cleaner,
I will be sure to take caution when I get to that step.
 
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Schluter documentation doesn't go very far to explain why you should do things their way, but if you call them, they will be glad to explain it all.

The reason for unmodified thin-set mortar for all Schluter is they don't want anything that requires drying. Thin-set will chemically use water to cure itself. Once thin-set is cured, is it very dense, hard, and also waterproof. The world didn't have Kerdi 100 yrs ago, they built stuff just fine without it. The fact that you are using Schluter products is already a great defense. Even if one does a piss poor Schluter job, it'll still last longer than a job that didn't use Schluter.

The only time you want to use modified mortars for tasks that call for thin-set only, is if you are doing commercial rush jobs. The mortar paste is so nice and fluid, spreads easily, some are even lightweight so you can carry more with you up the ladder. You get done quicker, the client won't notice it, and you get paid.
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A typical porcelain tile has a moisture absorption rate of less than 0.5% to be called porcelain. Then, take an impervious membrane like Kerdi. Using a latex modified mortar (there are other types of modified mortars that can provide strength before they dry) requires the excess moisture in the latex to dry out before things are fully stable (and, in severe cases, the latex can wash away before it cures), so, to ensure you have a stable platform, Schluter requires an unmodified mortar between its membranes and the tile. The TCNA says 7-14 days OR LONGER may be required for a latex modified mortar to dry sufficiently between an impervious membrane and tile. Most of the time, you won't run into problems, but Schluter is conservative...they know using an unmodified works ALL of the time in a KNOWN timeframe, but a modified does not ALWAYS work, they chose to specify an unmodified. Now, to attach something like Ditra to a plywood subfloor, they want you to use a modified, but also know that the wood will absorb and disperse any excess moisture, so things will stabilize just fine. And, in that case, the modified helps develop a stronger bond than an unmodified would to the plywood.

One way to get both types when only buying one bag of mortar is to buy the liquid modifier...substitute some of that for the water when mixing, and you have a modified...use all water on the rest, and you have the unmodified. Do not mix brands when you try this, use the admix specified. That's how they advertise one bag can meet various ANSI specs...how and what you mix it with.
 

Duffer

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Thanks so much for all your wisdom. I have the pan down and the Schluter membrane on the pan and curb.
Ready for the flood test and then then tiles.

You can see that I have Aquadefense on the wall and kerdi on the floor.
Are there any suggestions on use of the modified or unmodified thin set to install the tiles to the wall?

I would rather not have to buy two different bags for the job.
 

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Jadnashua

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If you buy the liquid admix for the brand of unmodified you have now, it becomes modified when you mix it up. By mixing systems, you've lost any warranty from either manufacturer, but I think you'll find they call for a modified over Aquadefense...you might as well try to follow the instructions for that on the walls. Will an unmodified work? Probably, but it's easy to make what you have modified and be sure. Just follow the mixing instructions to get the water/admix/thinset powder proportions correct.
 

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If you buy the liquid admix for the brand of unmodified you have now, it becomes modified when you mix it up. By mixing systems, you've lost any warranty from either manufacturer, but I think you'll find they call for a modified over Aquadefense...you might as well try to follow the instructions for that on the walls. Will an unmodified work? Probably, but it's easy to make what you have modified and be sure. Just follow the mixing instructions to get the water/admix/thinset powder proportions correct.
 
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jadnashua is correct. I don't know why people don't bother with whole pieces of Kerdi boards for the walls. They don't need any rubber paint coating tricks. Those trick paints aren't cheap, the Kerdi boards will cost just a bit more.

There is absolutely no reason to use anything other than un-modified thin-set, period. It would be silly to repeat the reasons, the replies above in this thread are correct.

It continues to surprise me how (end user consumers) think "advanced polymers" make a mortar "better", or how they think that are smarter than manufacturers. I like to take my advice from Schluter when using Schluter.

I like jobs that will last 75+ years or more. I'm sure glad I use only un-modified thin-set mortar. Best of luck.
ss_illu_shower_001_1_r_rdax_400x600_95.jpg
 
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Duffer

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Thanks guys,
I appreciate all the comments.

Makes the job a lot easier when I have the info that will best work.
I am prone to over - thinking the next step and second guessing my work.
But with all of your help I can dive in and get some work done.
 

Jadnashua

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When you build a shower, you are relying on the manufacturer of the products used to verify and certify that it works. They go to great trouble to design and test their products, and get them certified by an independent agency so that they qualify for passing building codes. Mixing systems could work, but technically, you do not use the whole system as specified, it does not pass the building code. Now, is a building inspector going to ding you for that, probably not, but they could. Lots of 'hybrid' showers out there, most work, some don't. Doing a one-off, you are the one on the hook. The companies involved have engineers that spend their lives figuring out what works and how to make it reliable and the test data to prove that it does. Why second-guess? IMHO, pick a system, and use it.
 
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