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Trouble with meters

#1
I've been involved with several recent projects where readings of 90% RH and higher have been questioned and additional testing by others has been ordered.

Oftentimes these other persons bring in testing equipment ( I won't say manufacturers' names ) and harvest readings that are much lower than my readings recorded using the Wagner Rapid RH probes.

This is very confusing for the facility owner and the principle decision makers. I launch into defensive mode, explaining with charts and test data how slabs that are very young (maybe only two months old) and exposed to the elements just cannot be 50% - 60% RH as the opposing tests indicate. My next step is to pick away at the other probe's faults: Were the probes calibration checked within the last 30 days? Were the probes properly acclimated at each hole? Were the holes properly prepared?

In the end the Wagner probes are always proven to be correctly reading the RH levels in the slab, but weeks have been wasted and hopes of the owner pushing forward without mitigation expense are dashed. Stress levels are high, feelings are hurt, and there is no joy in proving the RH is way too high to put flooring down.

I always do my best to convince the other testing companies to adopt the Wagner system so we all don't have to go through this uncomfortable and time consuming process again.

My point here is to test your slabs and question the results. There is no way a fresh concrete slab is at 50% RH, so find out why the probe is reading incorrectly and try to remove that problem from your future testing. Time, conditions and readings will always follow a trend and make sense. If they don't you have to throw up a flag and find out why.
JD Grafton
Concrete Answers for Flooring Problems
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#2
Yea thats gotta be frustrating CC. Too bad you do not have the same equipment they do so you could try and verify their mistake! Course I bet they didn't calibrate their probes, none of these fly by night inspectors out there do.

I agree that a new slab could never be 50% at a couple months, especially if it has a barrier underneath. Impossible! Unless maybe it was poured out here in the Sonoran desert in June!
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#3
I do have several of the Tramex meters sitting on the shelf. I became frustrated with those when my readings started swinging wildly and I had to provide answers to anxious clients. Now I stick with the Wagners and am very happy!
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#4
There can be an exception with polyester or polyproplene fiber filled concrete slabs found very infrequently fabricated in some tracts and other projects. Two characteristics include a very high consistent pH and a very quick low moisture content. The fibers provide a shaft or direct avenue for moisture to travel quickly upward and out. A microscope will tell shinny fiber like hairs above the troweled surface. Tensile strength is characteristically very low.
Just some interesting trivia.....
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#5
GP! Hows it going? I've seen that concrete a few years back, not lately. Awful stuff.
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#6
It is certainly a flaw in ASTM. Probes can't be compared. At world of concrete people were discussing how rapid rh measures the bottom of the hole while others might measure the entire hole. I'm convinced RapidRH probes read higher than they should. I've talked to some floor covering tech people and asked them to provide rH guidelines on a brand by brand basis but have been unsuccessful.
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#7
It's because the Rapid Rh reads the true value, not from the top to the bottom just as you said. Do some more reading.
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#8
(08-22-2010, 02:54 PM)eaadams Wrote:  It is certainly a flaw in ASTM. Probes can't be compared. At world of concrete people were discussing how rapid rh measures the bottom of the hole while others might measure the entire hole. I'm convinced RapidRH probes read higher than they should. I've talked to some floor covering tech people and asked them to provide rH guidelines on a brand by brand basis but have been unsuccessful.

The Rapid RH probes have been proven to provide accurate readings. Anything less is.... well.... inaccurate!
I have used many others that would show varying readings and I really couldn't explain to a client why all my probes were reading different RH amounts. Now I refuse to use any other probes.
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#9
Certainly, I agree. They need to rewrite the ASTM to make those "other" probe manufacturers re-design.

Just like you can't have a proprietary spec - a spec requiring the use of a proprietary meter will eventually fail a government public works spec inspection. (if a local sales rep does his job right)
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#10
(09-20-2010, 02:23 PM)eaadams Wrote:  Certainly, I agree. They need to rewrite the ASTM to make those "other" probe manufacturers re-design.

Just like you can't have a proprietary spec - a spec requiring the use of a proprietary meter will eventually fail a government public works spec inspection. (if a local sales rep does his job right)

Well guess what????

You know more than you think!!!

The spec is being rewritten as we speak. Wink
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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