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mver testing
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06-26-2015, 12:27 PM #1
jim decker Concrete Moisture Enthusiast *
Status: Offline Posts:42 Threads:4 Joined:Nov 2011
Recently had a commercial contractor with 40+ years call me regarding the following. It appears some company is trying to require a very expensive epoxy concrete sealer to an existing floor with vct tile, current floor down 15+ years, on it now which does not exhibit any symptoms of moisture coming from the slab.
Company conducting testing recorded mver readings from 5 to 15 lbs. I have never recorded mver ratings in El Paso more than 6.5 myself. Most rh readings run 25 to 55 here so he is considering rh testing as he is doubtful that these readings are conclusive.
El Paso is in the moisture map as having 5% to 9%  moisture content readings utilizing a Tramex moisture content meter so it does seem a little incredible to me that there can be mver readings this high.
Any thoughts gentleman???
Jim Decker

06-29-2015, 10:37 AM #2
rapidrhrep Concrete Moisture Tutor **
Status: Offline Posts:85 Threads:3 Joined:Aug 2011
[quote pid='3556' dateline='1435346826']
Jim:

First off, great topic for conversation.  So lets start with the  "current floor down 15+ years, on it now which does not exhibit any symptoms of moisture coming from the slab."  We have to keep in  mind all of the changes in adhesives and finished flooring products over the years.  I am not  saying our current available products are better or worse, just different.  So, the existing floor may have been installed on a slab that is wet by today's standards.  Once this finished floor was installed, it in essence, encapsulated the concrete, trapping the moisture.  Now that the floor has been demo'd, we have "uncovered a beast" in the form of excess moisture in the concrete. Now we have identify and deal with the issue.  Unfortunately, many times I speak with contractors during a renovation process and they aren't even going to do moisture testing on the slab because "the slab is old and the old floor is performing great.  It can't be wet."  I have heard of some very bad failure revolving around this thought process.

Speaking to the MVER readings, all I can say is that there are a lot of variables i.e how much surface prep, ambient conditions, calculations, etc.  RH will give you a better understanding of the moisture situation in the slab.

Lastly, has it been verified that there is an intact vapor retarder below the slab?  Slabs of this age may have never had one or what they had may be deteriorated.  If either of these is the case, the moisture readings being obtained may fluctuate anyway, so a topical mitigation system would ensure a successful flooring installation.

Hope this helps!

Jason



Recently had a commercial contractor with 40+ years call me regarding the following. It appears some company is trying to require a very expensive epoxy concrete sealer to an existing floor with vct tile, current floor down 15+ years, on it now which does not exhibit any symptoms of moisture coming from the slab.
Company conducting testing recorded mver readings from 5 to 15 lbs. I have never recorded mver ratings in El Paso more than 6.5 myself. Most rh readings run 25 to 55 here so he is considering rh testing as he is doubtful that these readings are conclusive.
El Paso is in the moisture map as having 5% to 9%  moisture content readings utilizing a Tramex moisture content meter so it does seem a little incredible to me that there can be mver readings this high.
Any thoughts gentleman???
Jim Decker
[/quote]

07-13-2015, 11:40 AM #3
eaadams Concrete Moisture Expert *****
Status: Offline Posts:600 Threads:88 Joined:Jul 2010
VCT has a lot of moisture outlets, 12x12 tiles hides a lot.  If they are switching products to a sheet, I'm not at all surprised.  Also, 15+ years ago adhesives were different.  MVER is really a useless test and highly subject to environmental conditions. 
The big issue with VCT is cost.  VCT is put out to bid at low cost and it becomes a race to the bottom.  Then the margin can be made on the change order.  If you put out a lazy VCT spec with tight moisture limits then you will get moisture change orders as people have to follow the manufacturer instructions.  

RH readings in 25-55 for probes inside of any concrete seem CRAZY low.  I've never had a single slab test under 70 in California.  

Regarding Jason's comments about an intact vapor retarder, I have a theory about that.  I think the ASTM test for RH is flawed.  The test is designed to simulate RH conditions of a PERFECT slab at the surface once covered; that is why we test at 40% depth.  

[Image: RH-Measurement-Depth-Graph.jpg]

But if there is no vapor retarder, if there is a blotter/sand/granular layer under the slab but on top of the vapor retarder, all of these things would affect where the potential equilibrium depth is in the slab.  I'd love to see the same charts done with blotter layers, sand layers, and with slabs exposed to subsurface moisture at various soil moisture levels.  I think we should have a deeper ASTM depth for renovations that have an unknown construction and perhaps have been drying from the surface for much longer.  I just think the slab equilibration Curve / Level for the non-perfect slabs would be different.  

07-13-2015, 02:51 PM #4
jim decker Concrete Moisture Enthusiast *
Status: Offline Posts:42 Threads:4 Joined:Nov 2011
VERY interesting!! Seems there are many considerations to factor. It is always ongoing especially from this forum. I've been away but learned a hell of a lot from you that do this testing on a regular basis. Keep the info coming.








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