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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

Messages In This Thread
Carbide moisture testing - CC Solutions - 09-18-2012, 10:19 AM
RE: Carbide moisture testing - eaadams - 09-18-2012, 11:01 AM
RE: Carbide moisture testing - CC Solutions - 09-18-2012, 12:25 PM
RE: Carbide moisture testing - eaadams - 09-18-2012, 02:02 PM
RE: Carbide moisture testing - CC Solutions - 09-18-2012, 06:11 PM

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