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Unread 07-25-2016, 04:51 PM   #1
john619
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High moisture slab?

I have a project coming up in a commercial building. 40 year old slab on grade, but high moisture. Tests are coming back at RH of 93% to 99%, PH = 9.

12x24 porcelain tiles are selected.

What is the proper way to deal with this kind of moisture?
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Unread 07-25-2016, 05:54 PM   #2
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There are products, such as Schluter's Ditra, that can help mitigate the effects of high moisture vapor emissions, but the maximum limits are generally expressed in pounds in this country when using a dynamic moisture test rather than the percentages used in the static test. And I don't know if anyone has ever established a correlation between the two.

You might call Schluter (800-472-4588) and ask what their limit is expressed as a percentage from static testing. They are a German company and are likely to have that number available for their European customers.

You sure you don't have a hydrostatic pressure problem under there?

My opinion; worth price charged.
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Unread 07-26-2016, 09:32 AM   #3
Sharon @ LATICRETE
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The use of LATICRETE STRATA_MAT can certainly help as long as no waterproofing membrane is required. Assuming the testing is being done as per ASTM F2170, the question is, why does a 40 year old slab still have so much moisture in it? Is the space above it enclosed completely and is there an HVAC system operating? Is it slab-on-grade and is there a membrane under the slab?
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Unread 07-26-2016, 10:16 AM   #4
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.
Quote:
Originally Posted by Sharon
..why does a 40 year old slab still have so much moisture in it?
Quote:
Originally Posted by Sharon
...and is there a membrane under the slab?
Think you've just answered your own question there, Ms. Sharon. But you're correct that we don't know if it's in conditioned space.

And I'm curious as to how the Strata Mat helps mitigate the moisture vapor transmissions if it is "vented" and not waterproof. Help us with that, won'tcha? I understand the theory behind the Ditra in controlling such vapor emissions, but it is waterproof and a vapor barrier.
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Unread 07-26-2016, 12:09 PM   #5
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Probably would be appropriate to mention regarding Ditra that it's "waterproof" only if the seams are covered with Kerdi. I would imagine that it's still an effective vapor management product without the seams covered.
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Unread 07-26-2016, 01:51 PM   #6
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My point was that with Ditra the material itself is waterproof and a vapor barrier whereas the Strata Mat material is not, Kevin. I'm wondering how the Laticrete products helps control moisture vapor emissions as it must be a different method than with the Ditra.

I would expect all the Ditra seams would need to be sealed per manufacturer's instructions for it to function properly in that regard, but I don't know that it would make any difference with the Strata Mat.

Perhaps Ms. Sharon will soon enlighten us.
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Unread 07-26-2016, 02:03 PM   #7
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Slab on grade, conditioned office building above. No way of telling if there is an existing vapor barrier. I would guess no as the moisture is so high. I have attached the moisture test for your viewing pleasure.
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File Type: pdf CSD HHSA- RH report.pdf (1.52 MB, 405 views)
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Unread 07-27-2016, 06:32 AM   #8
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Quote:
And I'm curious as to how the Strata Mat helps mitigate the moisture vapor transmissions if it is "vented" and not waterproof. Help us with that, won'tcha? I understand the theory behind the Ditra in controlling such vapor emissions, but it is waterproof and a vapor barrier.
The secret is in the “space” between the fabric and the bottom of the plastic composite which allows moisture vapor to move laterally instead of up. If a cement grout is used then some of the moisture vapor will work up and out through the grout. As a side note, the use of NXT Vapor Reduction Coating on the concrete will mitigate the moisture (RH) in the concrete and subsequent moisture vapor from the concrete. For more information on moisture in concrete then please read TDS 166 (attached) and for drying of concrete please read TDS 183 (attached).
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File Type: pdf TDS166.pdf (273.1 KB, 87 views)
File Type: pdf TDS183.pdf (437.3 KB, 96 views)
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Unread 07-27-2016, 08:07 AM   #9
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That's a LOT of moisture for a slab that old.

Not to step on the toes of the two people giving advice so far as I bow to their knowledge and ALWAYS helpful advice ....

... but I'd consider stepping outside and finding out why there's so much moisture coming up through the slab. Sure it may be a conditioned space vapor, but with that much moisture now trapped and being forced to migrate to exterior edges, you're (client) will have a moisture problem elsewhere, whether it be framing attached directly to the slab on exterior walls now taking on excessive moisture which will promote wet-rot, mold growth, etc.

The earth around the slab may need to be graded (re-graded) or even a sump-pump installed.

If you're lucky, you may find it's just a mis-directed sprinkler, weep hose or a crack in their water line that's soaking under the slab providing a constant wet situation. I say that as your profile puts you in San Diego ... so it's not likely a rain situation.

Hope that helps. Good luck!
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Unread 07-27-2016, 01:52 PM   #10
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Thanks all for your thoughts and ideas. I am going to let the GC and flooring subcontractors that will be responsible for the warranty determine how they would like to tackle this issue. The ceramic is just a small portion. It is predominately carpet tiles and LVT. I will advise as to their proposed method.
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Unread 07-28-2016, 06:33 AM   #11
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Good luck John!
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Unread 07-28-2016, 12:25 PM   #12
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Wow, 93-99s in a 40 year old slab is bad. Guarantee there is no vapor barrier underneath. They're going to have to do some type of remediation to that slab. There are many different methods for this, but it will likely need to be bead blasted and coated. I'm curious, what is the manufacturer's required Rh for your tile and setting material?
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Unread 07-28-2016, 02:12 PM   #13
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John, typically for a slab like this we'd recommend an epoxy moisture barrier like our Planiseal VS Fast:

http://www.mapei.com/US-EN/Floor-Cov...niseal-VS-Fast

This is a very common product for resilient floors. It would also work under tile. Let me know if you need any additional details about it.
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Unread 07-28-2016, 03:48 PM   #14
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John,

I suspect the problem is in the perimeter landscaping. I looked at a picture of this building and bet you a coffee I'm right. At first I thought maybe that river 400 ft. south might be a problem too, but now not so much.

Take a good look from outside, I bet the floor is close to or may be a bit lower than those shrubbery area all around the building. Even if the floor is a little higher, that landscaping will hold lots of moisture.

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Unread 07-29-2016, 07:12 AM   #15
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