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Specific humidity or ERH or Calcium Carbide?

#1
What is the most accurate or to be relied on?
From sensors placed in the floor, obtaining ERH levels, or calculating specific humidity (SH) and comparing it to ambient or undertaking a Speedy Calcium CARBIDE test? I am often coming across situations where ERH readings are up in the 90%'s, yet carbide and SH readings indicate bone dry? Can anyone answer this? ( Before anyone says, i have a method for undertaking the carbide test that does not allow distortion by heat from the drilling or crushing)
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#2
Welcome Andy,
I always recommend taking the tests that the flooring manufacturer bases their warranty on. If the manufacturer strictly uses the Calcium Chloride test, then I would definitely conduct that test according to ASTM F1869.

However - the CaCl test gives a extremely small indication of what the total moisture potential of the concrete is. The test reads only the top 1/2" of the concrete which can be dry as a bone, while the bottom of the concrete could be very wet. Installing a vapor retarding floor covering on the concrete will block much of moisture being emitted from the slab, and over time the moisture from the wet bottom will redistribute itself up into the dry upper horizon.

By using the Wagner Rapid RH Meter according to ASTM F2170, you can determine the internal relative humidity and what I like to call the 'Potential Moisture' of the slab. So I always recommend using Wagner Rapid RH testing even if the manufacturer only recognizes the Calcium Chloride test. You will have a much broader knowledge of what is happening with the concrete.
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#3
Thanks Cc, your right that one should base end results on makers specifications and other things mentioned in your reply.

But your answer doesn't really answer my questions.

The calcium carbide is a different test to the calcium chloride test and is a European DIN standard. I believe that some US drying Companies use this process as part of their monitoring program.

I use, remote monitoring systems for measuring ambient and structural temp, RH and ERH, Speedry infra red monitoring sensors that communicate with the drying machine (http://www.speedry.com) and measure the conditions stated and also specific humidity from the outside air, internal air within room and air within the sensor sleeve set in the structure - I use protimeter hygrosticks and boxes (but I do intend to order some of the Wagner sensors as they look and sound like they're worth trying out - do they show specific humidity on their readout?) and finally I use carbide testers to determine AMC expressed as a percentage. So, as you can see, this is pretty comprehensive. I use any combination of the systems during the drying or conditioning of floors and solid walls to determine that I have reached levels that are considered dry. (Here in the UK we usually have brick and block built walls which can probematical to dry out).

I've asked makers of sensors to answer, why ERH sensors can read unacceptably high, yet carbide tests indicate bone dry in the same area! No satisfactory answer given!

So, can anyone give me information that will answer the original question please?
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#4
Yes Andy I believe the differences you are seeing in test results are the product of the tests reading different parameters.

I was trying to correlate your findings with tests I am more familiar with, and extrapolate similar results.

My main point was that concrete varies in moisture content throughout the depth of the wall or slab, especially of the concrete is actively drying or is exposed to external sources of moisture. Using a number of different testing procedures and thinking what they are showing you is a good way to understand the forces in action.

No single test can tell you everything you need to know, and anyone working with concrete would be well served to conduct testing that will indicate the results they are required to know for the task at hand.

Can you explain how you use calcium carbide to test concrete? Do you pulverize the concrete?
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#5
CC,

At the start of our monitoring, 75mm (nearly 3 Inches) holes are drilled into the floor. I usually do 2 together in each test area. One for an in depth sensor to measure ERH etc and the other to prepare for my carbide test. The dust removed is collected, placed in a sleeve and then the sleeve with dust is placed in the second hole and capped. Once the floor is considered dry by ERH and specific humidity calculation, The second sleeve is removed and the dust is used for the carbide test.

There is no pulverising or drilling heat to distort the findings.

I also use surface boxes next to the drilled holes to measure surface ERH.

I also use a Tramax concrete encounter for further assurances.

Everything is used to provide a full, in depth record of validation. However, my concern is when other experts say "but the erh shows the floor is still wet" which then means I have have to waste time arguing against them.

I find that certain British Standards do tend to overlook the point you made that even though the surface is " dry ', there is often significant moisture in depth.
These flawed standards have allowed me several times to manipulate a main contractors liability in their favour to ensure the floor is at the flooring makers spec - even though technically, it is still wet.

But, what is causing the difference in the test methods? If the floor or walls being tested are wet, they're wet? Shouldn't the tests each pick up on this?

i'm finding such differences that it can become embarrassing trying to explain to customers who have access to their job via my remote monitoring systems, why erh's do not reduce to industry accepted levels...

So the question still remains.....

Now turning to the Wagner sensor, this would be a good means to easily work out the specific humidity in depth and compare it with ambient. Does the sensor have a read out for SH? or just temp and Rh or ERH?
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#6
Well that whole drilling and storing dust part would be a great place to find flaws I think. Isn't the carbide test more commonly used for soils testing? If I read you right, it sounds like you drill the concrete to harvest the dust, then store the dust in a drilled hole to acclimate it, then conduct the calcium carbide test on the stored dust.

The Wagner Rapid RH just reads relative humidity and temperature. You should be able to calculate specific humidity. But please bear with me when I ask: Why? Do you have manufacturers requiring specific humidity values?

As for the floor being wet and some tests not indicating it: These tests are designed and implemented over long periods of time. The CaCl test has been around for decades, and for decades installers have relied on it. Only now are we seeing the numerous flaws inherent with the test method. These flaws were well masked by high performance, high VOC adhesives in the States. As we study the rash of failures, we learn the flaws of the various tests and see shortcomings. We incorporate new test methods to help determine the suitability of our slabs to receive flooring.

For instance, a very dry concrete slab can produce very good MVER readings. But if this slab were on a broken water drain pipe or a sand bed that received a good soaking a month earlier the lower portion of the slab would be very wet. I know from experience that this happens every day with new slabs, no-vapor-barrier slabs, and blotter layer slabs. Our standard CaCl test will not pick up the lower moisture levels like the Rapid RH test will. And these lower levels of high moisture can definitely come up through the slab and destroy a moisture sensitive floor.

So our tests have evolved to expose problem areas. The tests I do now give me an excellent indication of the potential for flooring failure, and I am quite confident when I put my reputation on the line day after day.

I am now studying the calcium carbide test and specific humidity to see if I can use either to teach me more about my specific niche. Perhaps they will be useful. I learn something every day! Smile
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#7
For sure Cc. We are here to learn! No matter how long we have been in the trade!

I like to think that by storing the drilled dust, over the drying period it will acclimatize allowing an accurate carbide test without any heat distortion. You're right, there is a carbide test for soil BUT it is also designed for and is a great tool for moisture testing concrete. (Germany rely on it as the test method directed by the European DIN Standard).

Regarding specific humidity (SH), I must admit that makers / clients do not require SH measurements, but I do them purely because I want data and i'm trying to ascertain if this is more accurate. Data is King! Also the SH of concrete should be in equilibrium with the air. if it is not, it could be considered wet. I have been working with partners in manufacturing a new type of Dehum (http://www.speedry.com) and the machine interacts with infra red sensors placed in floors and walls, calculating SH and drying to levels set by the operator, So far, we have some pretty impressive results and the UK industry has endorsed the product by buying 150 units @ about $8000 each since launch 8 months ago. When we exhibited it at the RIA show a few weeks ago, the booth was mobbed!

Also, one of your chaps has patented ERP - evaporation rate potential formulae which mat have an impact on drying conditions / times.

Here in the UK we do not as a rule use MVER / Calcium chloride test as a method to rely on. (not saying no one is using it).

I believe the Wagner test to be a simple but good device allowing the user to derive the needed information and if needed, calculate the specific humidity.
Can I get a distribution agreement for the UK??? (I sit on the British Standards Committee putting together the PAS 64 and am well connected) The sensor is ideal for the damage mitigation industry (drying) where validation of drying is becoming critical as well as the flooring industry where many tend to just place in a simple Balls humidity box with temp /rh dials displayed. (these boxes often get knocked around).

You also importantly mentioned defects which must always be a consideration to be ruled out by the professional - with good monitoring techniques in particular!

Still, my initial question however is not answered - and i must say that i did not think (but I did secretly hope) that anyone would come up with the answer! (no offence meant cc). I'd be interested to learn of your thoughts once you had used a carbide tester or tried the SH route.

So, can anyone throw some light on the original question?
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#8
You are a breath of fresh air Andy!
You do mention that you find ERH readings that indicate the slab is wet, and your carbide tests indicate the slab is 'bone dry'.

I would challenge both of those tests! I would like to conduct your carbide test on a slab of known free moisture (tested by baking until weight loss stops) to see just how much free water was available and how much was indicated by the carbide test. Similarly I would test the ERH. I believe you are looking for answers with tests that confuse the facts.

My position is quite different from yours, and I approach the problem I have from another angle. I know when my concrete is at 75% RH or less, I will have no problems bonding moisture sensitive flooring to it. I will have a manufacturer's warranty, and a successful installation. I need not worry about specific humidity, vapor pressure, ambient humidity, or the rising price of a pint! LOL!

But of course things are not THAT simple! There are other factors I must be aware of, and I look for them. After all, it isn't really moisture that causes floors to fail anyway! Big Grin
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#9
Cc, I think we both agree that erh and carbide tests are questionable... as is c/chloride. alas, at this point in time I don't have the facility to do gravimetric tests as you suggest. Although I would like to do it myself (then I know it's right!). If you have the facility cc, I'd love to hear what results you get....

As an ex flooring guy, I understand the stance of 75% blah blah... .but here's the rub..... does the US standard - if there is one - state that the 75% is in depth or on the surface? Here in the UK is specifies surface - and we both know that in depth it may still be 80 - 90%. So, a flooring or building contractor who has to get the floor to 75% could theoretically prove he reached 75% on the surface, but had in fact, not dried the floor! Leading to a failure - which I have seen many a time. hope that makes sense.....

So, could SH be the new trend? Would it be more accurate? I'l hoping to ruin some tests on this in the near future so will keep you posted.
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#10
Hi Andy,
We use ASTM 2170 which specifies in-situ testing at a depth of 40% when the floor can dry from one direction, and 20% when it can dry from two directions (think cast in place suspended concrete floors).

As I said, this has been working extremely well for the industry, as long as tests are conducted properly, and that leads to my attendance on this forum - I do not work for Wagner or benefit from their sales, but I heavily promote the use of the Wagner Rapid RH system. It is very quick and easy to use, and gives amazingly accurate results. In my business I often must challenge users of the GE Protimeter and Tramex CRH. There are several others I see, but these two are pretty common in my area. I have never been let down by the Wagner Rapid RH meter, and I can assure you I have had my credibility on the line several times. 'Expert' testing companies come in and put their probes in the floor and tell the facility owner the slab is fine and I am holding up production! Of course this is always at the flooring stage of the game and the owner wants to believe all is well and the construction should continue. There is sometimes a lot of yelling, begging and threatening at this point. But time and again, the Wagner Rapid RH are proven to be accurate and my recommendations and warnings are spot-on.

I have used and I still own many of the other in-situ and electrical impedance meters, but I no longer use them. I cannot afford to stake my reputation on an inferior RH measuring device.
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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