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High Rapid RH readings??

It is meant to measure the density of soils. Used in Civil Engineering for soil site analysis. They also use it to measure how dense a concrete is like for a dam.

I would think it could be quite accurate if the tester has a control sample. Scanning over a dam to find honeycombing and voids would be easy, quick and accurate. Determining the moisture content of a piece of concrete would require exacting control samples for comparison wouldn't you think?
JD Grafton
Concrete Answers for Flooring Problems
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Yea I do think. There is a device out there where you take some concrete and put it into this pneumatic tube that cooks the moisture out of the concrete particles. I'll look for it on YouTube and post a link if I can find it.

(11-08-2011, 09:38 AM)eaadams Wrote:  Yea I do think. There is a device out there where you take some concrete and put it into this pneumatic tube that cooks the moisture out of the concrete particles. I'll look for it on YouTube and post a link if I can find it.

And how does that sample compare to the slab that naturally hydrates? I thought this test is to find remaining moisture. Taking a sample at the pour and drying it in 30 seconds won't replicate the concrete that dries over 2 years.
JD Grafton
Concrete Answers for Flooring Problems
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No you take cured aged concrete and pulverize it into this cylinder and then cook it off.

If you've ever seen someone in chemistry class figure out the number of Kcal in something by burning it off, same principal.

(I was a foodscience / textiles minor in college so I spent a lot of lab time lighting things on fire and doing elongation at break tests)

I am familiar with testing cured concrete, but the OP is referencing uncured concrete and attempting to determine the remaining water content with a density meter. To do that, you will need a representative sample that you can bake out the moisture and compare readings.

Every week. Or every time you want to test. Confused
JD Grafton
Concrete Answers for Flooring Problems
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ok so I installed a new probe yesterday. After 1 hour it already measured 90%. so off the bat, i know the floor is still too "wet" for my wood.

I will wait the required 72 hours for equilibrium and take another reading and let you guys know. I suspect it will continue to rise but I am curious to see if it hits the 99% that the other 3 probes are at.

For those wondering, the nucleodensimeter is being used by an independant lab hired by my client to verify (or challenge) my readings. Many people (including myself) find it hard to believe that the slab is still this 'wet' after almost 3 months of curing.

I can tell you one thing, after lots of research on other sites and consulting these forums, I'm truly starting to understand the actual timeframe (and process) needed for a slab to fully dry and be ready for a floor finish.

Thanks and I will report my new readings.

Hey ddemento,

A slab can dry about 1" depth per month under ideal conditions.
I can assure you that 3 months is NOT a long time for a slab to dry.

If the other probes are reading higher please read my post on hysteresis, it will ready you for the questions you will be bombarded with. The most important thing for you right now is to maintain your reputation and validity. They brought in another firm with this whirly beepy thingy and this guy will be using seven syllable words and trying to convince the principals he knows what he is doing. Don't let him.

Get us your readings and let's talk this through long before the big meeting. You are right, don't be intimidated. It is what it is, and three months is nothing in slab drying land.

You can call me if you want to go over your results and you need to prepare your approach to the dilemma. Contact me via email for an immediate response.

By the way, you can go read that probe in a couple of hours and get a good reading. It's close to the final reading within the first couple of hours. That will give you an extra day to prepare your explanation. Wink
JD Grafton
Concrete Answers for Flooring Problems
[email protected]

6" slab, enclosed structure, how burnt is the slab? Post some pics is it dark?

Who is the wood manufacture? Post the spec I'll do some foot work for ya. Post the spec.

ok so I went to the school today to take my readings of both the existing probes and the new one installed on Tuesday. I did not expect the existing ones to be any different (although I do always hope for 'some' movement) and they were still at 99%.

Then i measured the new probe. It measured 99% and at that moment I think my stress level went up by just as much! I was truly hoping for a lower reading.

I asked myself: is it possible, there is some sort of malfunction on my reader?

I decided to take a reading from an unused probe in my kit to see, and it read 47%, so the reader must be working fine.

(Curiously, my air humidity registers at about 37% when using a hygrometer, but I guess its alright to have a difference between the two since the probe is probably not meant to read humidity of ambient air. Right?)

Anyways back to topic. How can it be after almost 3 months, the RH of the slab has not even shown a flicker of change? I know (from my recent research) that its 1 month per inch of slab for full drying, but am i to expect the readings to drop suddenly "off a cliff" with the next 3 months?

Someone please some insight into what may be going on.

For those asking, I attached some pictures of the slab and the link to the wood manufacturer's website:


PS. Thanks to all of you so far for the help with my issue and others. I am truly impressed with the dedication!

.jpg   IMAG0547.jpg (Size: 446.81 KB / Downloads: 12)

.jpg   IMAG0545.jpg (Size: 406.09 KB / Downloads: 11)

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