How to measure moisture in concrete

Video Link

Complete Concrete Moisture Test System - The 5-Point Test

  1. Ambient conditions - Dew Point with a Hygrometer or Tramex Feedback DataLogger or CMEX5 with a built-in Hygrometer
  2. Surface Temperature of the slab - Infrared Surface Thermometer
  3. Percentage Moisture Content - %MC of the top 3/4" with the Tramex Concrete Moisture Encounter - CME5 and CMEX5
  4. %MC In-Situ with the Tramex Concrete Moisture Probe
  5. % RH In-Site with the Tramex Hygro-i2


Below is the transcript of the video:

Hi, I'm David from Tramex Meters and today I'm at RTI and we're going over a 5-point concrete moisture test to quickly determine the moisture condition of a concrete slab.

For the first step, we're going to be looking at ambient conditions, and it's important to understand that these conditions can change and that they will affect the results of the test. The necessary tool for this is a hygrometer, which might be attached to a moisture meter in this case, or it can be a separate hygrometer. But the main points we're going to be looking at are temperature, relative humidity, and dew point. And here we're looking specifically at the dew point. So, I have two meters here one is our feedback Data Logger, which I'm looking at on the App and it's showing me that the ambient dew point is 50 degrees Fahrenheit, and also on my CMEX5 concrete moisture meter we're getting 50 degrees for the ambient dew point through the hygrometer on that meter.

The second point, we're going to look at is the surface temperature of the concrete slab and again, this is important in relation to the dew point, to protect against any condensation issues that might be happening even not visible to the naked eye. So, I'm going to use the infrared surface thermometer and shoot the temperature, and you see we get 77 degrees Fahrenheit for our surface temperature, and we're just checking that against the ambient dew point, which we've noted is 50 degrees Fahrenheit. So, we're at least 10 degrees above that ambient dew point with the surface temperature, and we know that we're not going to have a dew point issue, which is gathering condensation on the surface of the slab.

So, the third point we're looking at is the percentage of moisture content in the top three-quarter inch of the slab, and we're doing this using our Concrete Moisture Encounter depressed to the surface of the concrete. Now, we want to make sure that it's a clean dry surface, free of any drywall mud, paint, or any coating on that surface that needs to be removed, so we can get a good indication of moisture. Now, keeping in mind that this will give an indication of surface moisture and it can be caused by ambient conditions, or it could be coming from below the slab, and we're going to take readings at each location around the clock, 12 o'clock, three o'clock, six o'clock, nine o'clock, and we're going to keep the highest reading.

The fourth step we're going to look at is the Concrete Moisture Probe, which we call The Determinator. Now, this instrument is basically an extension of our Concrete Moisture Encounter that drops the reading to the depth in the concrete that you desire to take a reading. Because of the specific size increments of the Concrete Moisture Probe, we can use this guide of slab thickness to determine the appropriate length for the Concrete Moisture Probe. This reading should give us a number in a healthy piece of concrete one-half to one percent higher than the surface reading. If you see a number higher than that, this is going to indicate that your moisture is coming from below the slab. If you see a number lower than that, it's going to indicate that your moisture is coming from above the slab. So, for example, in this case, we wetted the surface and took readings with the Concrete Moisture Encounter, which maxed out our meter at 6.9, which gave us an indication of high moisture in the surface. We then, to determine the source of that moisture, attach the Concrete Moisture Probe and take a reading within the slab, and saw normal percentage moisture content numbers. This will indicate to us that once that surface moisture is dried we'll be back to the normal percentage of moisture content numbers.

For the fifth step of our concrete moisture test, we followed ASTM F2170 for in situ RH readings. We did this by drilling a hole to 40% depth of the concrete slab, then inserted a sleeve, and capped that sleeve. Now, we wait 24 hours to insert the RH probe and this allows the heat created by drilling that hole to dissipate, so it doesn't affect our readings. After 24 hours, we come back, insert the RH probe, and take our readings, and this can be gathered with the rest of our data points so that we can make consideration of the actual moisture condition of the concrete slab. 

To recap today we were looking at five points of testing moisture in a concrete slab. The first point we looked at was ambient conditions, taking a particular look at the ambient dew point and comparing it to the second point which was the surface temperature of the slab, making sure that the ambient dew point was at least 10 degrees above that surface temperature. The third point we looked at was moisture content in the top three-quarter inch of the slab using the Concrete Moisture Encounter. The fourth point we looked at was the Concrete Moisture Probe, taking actual moisture content within the slab, and the last point we looked at was an in-situ RH probe, giving us the RH percentage at 40 percent at the depth of the concrete slab.