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Carbide moisture testing
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09-18-2012, 10:19 AM #1
CC Solutions Concrete Moisture Evangelist *******
Status: Offline Posts:1,067 Threads:69 Joined:Dec 2009
Flooring and adhesive manufacturers have determined tests they honor by choosing tests that reveal the slab conditions which may affect flooring performance. They don't test for color. They don't test for compressive strength. They don't measure the thickness.

What flooring manufacturers wanted to know for about 60 years is how much moisture was in the slab. The previous test of choice was the absorption test using calcium chloride (CaCl) pellets in a dish placed under a plastic sheet (later a dome) which gave a rough indication of the amount of moisture coming from the concrete. They knew that fresh wet concrete emitted a lot of moisture, and in a number of ways that moisture damaged flooring and adhesives. The CaCl test was a way to try and quantify the amount of slab moisture by measuring the rate of moisture emission as the slab equilibrated with its surroundings. This worked well as long as it really didn't matter! We had different adhesives then and they were very alkali resistant.

When we switched to more environmentally friendly adhesives we began to have an increasing number of flooring failures associated with moisture. The old CaCl test wasn't revealing the true moisture level of the concrete as it was easily fooled by steel troweled concrete, sealers, dirt and debris from construction activities and ambient atmospheric conditions.

More recently in this country, we have realized in-situ, or inside-the-slab, moisture testing is a much more reliable and accurate determination of the moisture remaining in the concrete, and more importantly, we have seen that even concrete with a low moisture emission rate can fail miserably if the internal moisture content is high. I call this moisture content the 'Potential' a slab has for failure. High moisture content means the slab has a high potential for failure.

Some folks in the flooring moisture mitigation industry have started asking us to perform the carbide test (D-4944) to prove their mitigation system is functioning. This test is commonly used to test soil moisture. It is not a recognized test by any flooring manufacturer that I know of. While the test may accurately reveal moisture in a sample of concrete that is tested, we need to consider what the results mean to us, and then how we correlate the test data with our know requirements for flooring moisture requirements. This is a job better left to scientific labs!

We do know that a concrete floor remains wetter at the lower horizon of the slab and it dries from the top. We also know that at a depth of 40% of the thickness of a concrete slab we find the same amount of moisture as we will find when the slab is sealed and the total moisture is allowed time to equilibrate throughout the slab. These facts have been proven and documented, and are the basis for F-2170 in-situ RH testing.

My questions then for the proponents of carbide testing are:

1. From where within the slab do you harvest the concrete specimen for testing and why?

2. What mechanical means do you use to harvest the sample, and does that affect the moisture level of the sample?

3. What correlation between test results and manufacturer's requirements can you show?

JD Grafton
Concrete Answers for Flooring Problems

09-18-2012, 11:01 AM #2
eaadams Concrete Moisture Expert *****
Status: Offline Posts:600 Threads:88 Joined:Jul 2010
They don't test for color.
- color is used as a basis of examination though, burned slabs and dusty slabs have distinct colors.

They don't test for compressive strength.
- they do require compressive PSI tests.

They don't measure the thickness.
- I think they do in that we look at slab construction for floor recess, curling issues, joint spacing & other joint issues.

I'd like to add a 4th question:

4. What is the cost and who carries the burden.

I add this because one of the largest issues with getting GC's to use RH testing is the cost. They have all been doing CaCl testing for years by 'throwing a test kit on the floor'. While doing it wrong it is still cheap. Carbide testing sounds expensive to me and as such should be the sole purview of the PE doing the owner's testing. To put this burden on flooring or mitigation people will only cause the same issue we have had with CaCl. CaCl is not done because it is correct but because it is cheap (and even cheaper to do wrong). You will never get good acceptance of Carbide testing if the burden falls to the GC's or subs because flooring manufacturers will have to keep allowing CaCl and RH testing (since everyone uses those now) and the GC will always choose the low bid, cheap way to do something.

Wood Flooring Reference to Carbide Testing: http://www.fastfloors.com/media/fastfloors/installationguidelines/hardwood/04-Chap3.PDF

09-18-2012, 12:25 PM #3
CC Solutions Concrete Moisture Evangelist *******
Status: Offline Posts:1,067 Threads:69 Joined:Dec 2009
My contention is that using a cheap test that is close to worthless is more expensive than doing a better test that may cost a tiny bit more initially.

Why not just test the floor by throwing wet chicken feathers at it and seeing how many fall facing due north? I think the same number of flooring manufacturers recognize that test.

The cost of the test is irrelevant if it doesn't provide the results you need to go forward.

JD Grafton
Concrete Answers for Flooring Problems

09-18-2012, 02:02 PM #4
eaadams Concrete Moisture Expert *****
Status: Offline Posts:600 Threads:88 Joined:Jul 2010
Using a test that is so expensive to do that it is never used is almost the same as chicken feathers.

The point is the specification, to put such a test on div 9 is absurd. It is bad enough I am loosing work by almost the exact cost of my Wagner meters because the cheap sob's just throw a kit on the floor.

If you were to compound it with a new "carbonate" test it would further break the system. Bad enough that I have to talk to structural engineers who don't know what RH is, I talk to concrete contractors who don't know what RH is, the only people who know about RH in my part of California are flooring people and most choose to not use it to guarantee they have lower bid prices. If I had to do a Carbonate test my bids would only go higher.

And don't fool yourself into thinking you can add a 'carbonate' test without the flooring mfg's still listing #/% numbers. Manufacturers would love to add a 3rd test it gives them another out on claims.


09-18-2012, 06:11 PM #5
CC Solutions Concrete Moisture Evangelist *******
Status: Offline Posts:1,067 Threads:69 Joined:Dec 2009
Perhaps you misunderstand my position on carbide testing....

It is a soils test being spec'd by silicate pushers because they think they can fool people into believing it means something.

The way they are testing means nothing to anyone in the flooring industry.

As for CaCl testing, it is nearly worthless for determining the potential a floor has for failure. I'd rather put in 5 Wagners at a cost of $200 (including installation and reading) than 7 CaCl tests for the same cost, when the CaCl tests tell you nothing about the condition of the slab, and the results are unreliable.

JD Grafton
Concrete Answers for Flooring Problems

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