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Reliability of RH Testing Using Removable Proves vs. Insitu Probes?

#1
Hello friends:

I am being aksed by a general contractor (infact by the product manufacturer) to use one RH measuring product over the other and I am not sure which one is more reliable. I fundamentally agree to using RH testing as a means to evaluate the concrete floors prior to installing flooring over it. However, when given a choice between using a removable RH probe (using a sleeve like IntelliRock Humidity Loggers or GE Protimeter) versus Insitu probe (like the one by Wagner), I am not sure if one is better than the other or, both provide similar results? Both product manufacuters claim that their probes are calibrated, but I believe the way these probes measure the RH is different (correct me if I am wrong).

We had a conflicting situation on a project where the removable probes gave lower RH readings (in lower 80% range) versus insitu probes (in lower 90% to upper 80% range) on a newly constructed slab-on-grade at similar temperatures. From what I understand, the Rapid RH probe measure the RH at 40% of slab depth while the other removable probes provide an average of the RH through the entire depth of the drilled hole. So I am inclined to say that since the surface is drier compared to the bottom of the hole, the average RH will be lower compared to the RH at the bottom of the hole. But the question is.....which reading should I use for making a decision on laying the flooring? Is the 75% RH requirement per F2170 valid for which test method???

Untill this project came across, I had been using the Rapid RH insitu probes, but I need enlightening from you experts on which kind of product is better and how to interpret the results?

Thanks
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#2
>>>So I am inclined to say that since the surface is drier compared to the bottom of the hole, the average RH will be lower compared to the RH at the bottom of the hole. But <<<

Exactly
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#3
I would suggest getting a copy of F2170 (http://www.astm.org/Standards/F2170.htm). Section 10 specifies 40% of a slab drying on one side and 20% of slab drying on both sides which is then followed by:

"Testing AT these depths will indicate the potential equilibrium relative humidity that will be established within the concrete slab after a low-permeability floor covering is applied."

it doesn't sound like "an average of the RH through the entire depth of the drilled hole" is what they mean.

by the way,there is no reference to 75%RH in F2170.
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#4
The 75% requirement is set by adhesive manufacturers and varies with each product used.

The Rapid RH does a very good job of isolating the test sensor at the 40% depth (or 20% when drying from one side). It is true the sleeve readers take a long time to acclimate, and must have had the calibration checked within the last month. They must also be watched for drift.

I have used many different Rh testing devices and have found the Wagner to be far and away the most reliable, repeatable and accurate device for testing RH.

My livelihood depends on accurate RH readings, and oftentimes I find myself in direct conflict with several other RH reading devices on a job site. Many times I have had to prove my RH readings, and the Wagner Rapid RH has never failed me. It's the only one I will use or recommend. [/quote]
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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