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measurement in a cold slab

#1
Hello All, my first time using the rapidRH on a concrete slab. The RH came back as 90% rh at 51 deg F. We were planning to coat this floor with epoxy. The building is on top of a hill and on all sides the terrain is slopped down and away. The heat is turned down since they are not currently
using it. Is there a correction I can apply to my readings to correct for
the cold conditions.
Thanks
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#2
You didn't mention the ambient conditions during the required test period of 72 hours. If the slab is 51 degrees, I would guess the ambient condiitons of the space are not within ASTM F2170-11 standards. The space MUST be placed in operating conditions for 48 hours prior to conductiong the RH test and remain at operating conditions during the 72 hour test period. You need to refer to the document and follow the standards outlined.
JK Nixon
Concrete Restoration Services, LLC
Pittsburgh, PA
http://www.rhtester.com
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#3
Welcome Noweare!

Your question is a very good one, and a problem I have been working on but haven't finalized.

You probably know that warm air can hold more moisture than cool air. The same amount of moisture will have a higher RH in cool air than warm. But for some reason the relationship in a concrete hole is not the same as in the atmosphere. This may be due to the particles that make up concrete itself, absorbing and holding water or releasing water depending on the temperature.

What I can tell you is that as the concrete warms the RH will tend to drop, but not by as much as one would think.
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#4
Thanks for the replies guys. Reading through some of the threads on this forum
shows that this moisture thing isn't as straight forward as I would like Smile There seems
to be many variables involved besides just a simple measurement.

I am a contractor and I was doing this to try to protect me from installing where I shouldnt and
save the customer possible problems if it fails.

I'll keep reading and hopefully I will see the forest for the trees but in the mean time I have
told the customer the enviromnment must be at operating conditons for 48 hrs before the
measurement is taken, that I do not guarantee against acts of nature (moisture) even if the
RH reading is acceptable and it's their call to go forward or not.
call to go forward or not.

Joe McCarron
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#5
That's exactly right Joe! You are doing the right thing. Just let the client know that the temperature of the concrete should be at service temp for the most dependable readings. You could extrapolate a little (the ASTM has some flexibility) and you know which way to extrapolate whether the concrete will be warmer or cooler during service.

I have seen guys take readings on 80 degree slabs that are low, then when the slab cools to 67 they are high. If your readings are coming in close to the cut-off point you will want to get that slab at service temp.
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#6
Does anyone know where slab 'service temp' is specified in CSI specs?

Just wondering where you look for that. If you have an HVAC that will be set at some level, will that HVAC impart some surface slab temp?

I'm just asking about slabs on grade. In California we do a lot of summer work in the Dessert. But when the Dessert goes into the winter & at night it gets cold. And we all know how a slab temp will just end up at the ground temp. 15mil plastic doesn't insulate anything.
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#7
That's a great question but I'm not so sure CSI would stick their neck out and have a spec for the same reason they will not specify an optimum concrete surface profile for optimum slab hydration. Reason being that what if a flooring failure occurs despite meeting their defined spec? Who's liable? Could really open up a Pandora's box. Besides, as I see it, service condition would be different for (i.e.) an epoxy coating for a dairy plant vs. an auto d!ealer service area.

If someone knows of a defined spec, I'd love to see it.
JK Nixon
Concrete Restoration Services, LLC
Pittsburgh, PA
http://www.rhtester.com
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#8
Me too!
Stephen Perrera dba
Top Floor Installation Co.
http://www.tucsonazflooring.com
http://www.floorsavior.com
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#9
No I wasn't asking for the spec. Just where would it be located? That way I can RFI for the expected service temp of the slab.
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#10

.jpg   AcceptabletemperaturerangeswithinASTMF1869protocol.jpg (Size: 91.02 KB / Downloads: 21) .
Stephen Perrera dba
Top Floor Installation Co.
http://www.tucsonazflooring.com
http://www.floorsavior.com
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