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04-29-2013, 04:27 PM #11
eaadams Concrete Moisture Expert *****
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(03-19-2013, 08:38 PM)CC Solutions Wrote:  No vapor retarder under concrete can end up being a disaster. Especially in buildings that are dehumidified often.

At world of Concrete Peter Craig said no vapor retarder invalidates the accuracy of RH testing. Scared the pants off of me.

04-29-2013, 07:01 PM #12
CC Solutions Concrete Moisture Evangelist *******
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(04-29-2013, 04:27 PM)eaadams Wrote:  
(03-19-2013, 08:38 PM)CC Solutions Wrote:  No vapor retarder under concrete can end up being a disaster. Especially in buildings that are dehumidified often.

At world of Concrete Peter Craig said no vapor retarder invalidates the accuracy of RH testing. Scared the pants off of me.

If you think of why he said that it makes sense:

The RH probes are set at a depth where the RH measured will be the same today as it will be when the slab equilibrates.

With no vapor retarder, the moisture level is unlimited, so you cannot predict what it will be in the future. Wink

JD Grafton
Concrete Answers for Flooring Problems
JGrafton@ccsolves.com

04-30-2013, 09:15 AM #13
eaadams Concrete Moisture Expert *****
Status: Offline Posts:592 Threads:85 Joined:Jul 2010
And establishing that there is an effective subslab vapor membrane under the slab is NOT in the astm.

It should be. Apparently the way to do it is to core each slab.

That will drive up testing and set the whole rh testing process back.

I'd also like to say that in CA we have a ton of slabs with 2" sand under them and on top of a vapor membrane. So rh testing can't be accurate at 40% in such slabs. Perhaps on those slabs it should be 80% or more depth.

05-01-2013, 05:57 AM #14
CC Solutions Concrete Moisture Evangelist *******
Status: Offline Posts:1,065 Threads:69 Joined:Dec 2009
There are a host of problems with blotter layers as they let moisture freely travel under the slab.

Installed perfectly they would work well but cause the concrete to dry more slowly.

But they are never installed perfectly. A puncture in the vapor retarder under a blotter layer will allow a huge amount of water into the blotter layer, whereas a hole in a blotter layer directly against the concrete will be nearly insignificant.

As far as RH testing goes, you need to reference the conditions assumed and indicate the requirements set forth by the flooring manufacturers and ASTM F-710. If the moisture levels change due to improper construction detail or workmanship error, you can hardly be held liable.

JD Grafton
Concrete Answers for Flooring Problems
JGrafton@ccsolves.com

05-01-2013, 06:16 AM #15
CCR Concrete Moisture Coach ***
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This exchange is most disturbing since so many tests I perform are done on older slabs with no vapor barrier. Seems like we have taken a giant step back based on Peter Craig's comment.

JK Nixon
Concrete Restoration Services, LLC
Pittsburgh, PA
http://www.rhtester.com

05-01-2013, 06:24 AM #16
CC Solutions Concrete Moisture Evangelist *******
Status: Offline Posts:1,065 Threads:69 Joined:Dec 2009
I always point out to clients that the flooring manufacturer requires an intact, proper and functioning vapor retarder directly under the concrete slab.

I also point out that even with a vapor retarder, there could be areas that were cut or punctured or joints that are wide open where moisture can get into the slab.

You can still read the RH, but if something is wrong that you can't see problems may arise later on.

JD Grafton
Concrete Answers for Flooring Problems
JGrafton@ccsolves.com

05-01-2013, 10:15 AM #17
rapidrhrep Concrete Moisture Tutor **
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(04-30-2013, 09:15 AM)eaadams Wrote:  And establishing that there is an effective subslab vapor membrane under the slab is NOT in the astm.

It should be. Apparently the way to do it is to core each slab.

That will drive up testing and set the whole rh testing process back.

To Evans first point, we all need to remember that every ASTM standard that deals with moisture testing of a slab, in relationship to flooring installation, is really a sub-standard, if you will, of the BIG standard, F710. In there they do reference E1745, under referenced documents, and in the appendix they speak specifically about moisture retarders.

The second point he made, many times I have heard Peter make the comment, "if I only had one test available and I had to pick, it would be a core test".

The third point about setting RH testing back, I'm not sure I agree with. Whether its RH or MVER testing, an intact vapor retarder is a critical piece for ensuring proper measurements, much like "service conditions". Obviously, RH is not impacted as much by ambient conditions and is a much more reliable test method for future predictability of flooring performance, in relationship to moisture.Big Grin

As JD eluded to, all manufacturer's, maybe without being explicit, are implying the need for a vapor retarder, among other things, when they call out F710.

Obviously, this is all in my humble opinion and from the confines of my VERY orange world.

Jason

05-02-2013, 03:42 AM #18
CCR Concrete Moisture Coach ***
Status: Offline Posts:236 Threads:14 Joined:Dec 2011
Vapor barrier or not, it seems to me RH testing is still the best testing option. Even with a quality barrier, finishers are still troweling new concrete too tight to let moisture escape. Literally every new slab I test is in the 90s. On big jobs, these slabs can be over 12 months old.
I'm in the midst of testing an interesting job with 2 different vapor barriers (6 mil and 15 mil) from well known manufacturers. In addition, concrete has 2 different finishes in different flooring areas (CSP 3-4 and slick, power-troweled). Testing will take place when the building is enclosed and conditioned. I can hardly wait to do this one.

JK Nixon
Concrete Restoration Services, LLC
Pittsburgh, PA
http://www.rhtester.com

05-02-2013, 05:53 AM #19
CC Solutions Concrete Moisture Evangelist *******
Status: Offline Posts:1,065 Threads:69 Joined:Dec 2009
Does that 6mil barrier somehow meet the spec?

We could almost always get a slab dry in 4 months by using a 3 day wet cure and keeping additional water off it. We left the surface porous and breathable.

I bet you will see a marked difference in RH on your test slabs CCR.

JD Grafton
Concrete Answers for Flooring Problems
JGrafton@ccsolves.com

05-02-2013, 06:33 AM #20
CCR Concrete Moisture Coach ***
Status: Offline Posts:236 Threads:14 Joined:Dec 2011
(05-02-2013, 05:53 AM)CC Solutions Wrote:  Does that 6mil barrier somehow meet the spec?

We could almost always get a slab dry in 4 months by using a 3 day wet cure and keeping additional water off it. We left the surface porous and breathable.

I bet you will see a marked difference in RH on your test slabs CCR.

No it does not. There was a communication breakdown somewhere between GC, concrete contractor and who knows who else. About 60% has 6 mil, rest is 15. I am definitely anticipating lower RH in the open profile slab. It was left rough and lower to accommodate thin set and ceramic. I am anticipating also they will need to install a mitigation product to help fend off future issues where the 6 mil was used, as well as the super tight finish of those surface areas. I expect the concrete contractor will be biting the bullet on that expense.

JK Nixon
Concrete Restoration Services, LLC
Pittsburgh, PA
http://www.rhtester.com








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