Modified/unmodified

skcolo

So I've been building some showers with Mapelastic waterproofing and mesh, some with Wedi, some Noble. All of these claim to be waterproof, just like Kerdi, but with Kerdi, you need to use an unmodified thinset since you are sandwiching thinset between two non permeable surfaces and the thinset cannot get air to dry. I use Ditra on the floors a lot, and have been using unmodified for the tiles without problems, but I haven't ventured into the Kerdi showers because I like the system I already have.

These other systems allow for modified thinset. I guess I really don't see much difference as far as air getting to the thinset. Maybe I am missing something. Thoughts?

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Inner10

You aren't missing anything, its a Schluter thing.

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angus242

Call Schluter. Have them explain it to you. I still don't get it.

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Angus

skcolo

I was hoping you would have the answer.

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angus242

Their answer is modified cannot fully cure when sandwiched between a waterproof membrane and tile. Unmodified self cures.

What they've never been able to address is why every other company allows it if it's really such a bad situation. I always try to give 2 days to cure before grouting when using modified over a membrane.

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Angus

Inner10

Anyone ever put some modified mortar in a sealed container and see how it cures?

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angus242

That's not really the point.

But I have put plenty of porcelain over membranes using modified. There have been a few times the following day, I found a tile I didn't like and removed it. In 18-ish hours the thinset was not cured. It was set enough to support floor tile but still needed time to fully cure. This is why I won't grout for 2 days.

If time is a real issue, rapid set thinset can be specified. It's only a few dollars more per bag and doesn't break the budget.

For those that have access to, Ardex makes some wonderful thinsets. Worth looking in to.

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skcolo

Thanks Angus. I have heard about using rapid set, but I haven't yet. I too, have been waiting a few days for grout. I have been using a lot of these 12 x 24 tiles lately in showers and was just concerned about the modified over a barrier thing.

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kevjob

Steve we use versabond over kerdi all the time. If we use anything modified more we give more time to cure before grouting (2 days or so) and havent had any issue and if we did with unmodified I wouldnt be waiting for Schluter to do anything warranty wise

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Floormasta78

253 Gold over and under Ditra..

Wait two days them come back with Spectralock pro grout and you got yourself a lifetime tile installation

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JWilliams

So sayeth the MASTA!

Inner10

But the warranty! Ohhhh the humanity!

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Floormasta78

Schulter might not even be around next time this new home gets flooring again..

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ohiohomedoctor

In theory Schluter is right. In practical application everyone else is right..

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Floormasta78

Well in theory, we are not all greeks.. So forget that !

We practice what we preach. I'm Father Floor Master.
Now let's pray for all those hacks out there...

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Groutface

Schluter will be around for the next ice age and they will make freezethaw stable showers......huhuh

Ethos

I use unmodified over ditra simply because it's what the manufacturer recommends and that's typically what I go with, but seriously, I don't see why it would be a big deal. Eventually that moisture will escape out the sides, no matter what, and damp modified thinset is still crazy strong after just a few hours. We all know that manufacturer recommendations tend to be overkill. They have to, because they know that idiots will push anything to it's limit and the easiest solution is to set that limit past practicality.

It's kind of like how most rope will easily hold double its test weight. Thinset almost always says no walking on tile for 24 hours, but I'll bet a lot of us walk on tile that's been down for 12-14 overnight. Having removed a few tiles I didn't like over the years, I can say that 12 hours and even the fattest man doing windsprints across the floor isn't making that tile move.

It's all CYA.

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