Strange Moisture Issue

Inspectors: I measured moisture in a basement carpet at 20 to 25%. The problem is that the pad under the carpet was bone dry as was the cement floor. The owner then had a commercial dehumidifier installed for several days, and I went back to test it again. My readings were the same as before. I used two different meters. Humidity was 44-45%. Thermal camera showed no moisture anywhere in the basement. Could it possibly be the material in the carpet causing this false reading? Never have come across this before. Thank you.

Check the depth of your meter. Some will take moisture readings through a half inch to two inches. You may just be reading the concrete through the carpeting

Thanks for the reply Ian. That is part of the problem. The pad under the carpet in that exact same area and the concrete are bone dry. I checked to make sure that I had tested each one on its own.

When taking moisture readings you need more information. All meters are affected by their surroundings.

First you need to post the ambient air temp and humidity levels, high levels of interior humidity will give a high reading with all meters but more so with induction meters.

Second you need to post the type and model of meter you are using.
Induction or pin-less meters are “dumb” they read everything in their path from pad to pad in a loop.

Pin meters are slightly less dumb they read between the two pins directly.
The materials you are testing affect the readings so there is testing scales and equipment for most type of materials but i am not familiar with one for carpet.

You are welcome to email me direct if you want to talk about this…

Moisture is always present in concrete. You are probably getting a false positive from the concrete. Be careful not to touch the concrete with your pins. You can only check carpet effectively with a pin meter. The best way is to pull the carpet and pad back and test. Start with your nose though. If there is moisture in a basement carpet, it will quickly announce itself to your nose. Also, check the humidity and grains per pound of air moisture if you know how to do this or have a meter that can. That can tell you the most about how swampy the basement is. Check your low walls and plates as well. If they are wet, then you probably have a wider issue. Again, use your pins, not the surface aspect of the meter. There is a time and place for both. If your pad is not wet, then your carpet is not wet. And 70 pint dehumidifiers should always be the minimum in a basement. Anything smaller, typically can’t handle the volume of air in a basement. There are actual calculations for this. People try to run 35 pint machines or less and they don’t do the job. Also, due to the human factor of laziness, always suggest a self pumping unit. People simply don’t keep up with emptying these guys.

There was another post asking which moisture meter you are using. Do you have that info?

Is there a dog in the family? I got caught out like this once before, thinking there was a moisture problem in the basement on carpet when the slab was dry. Turned out to be that old chemical symbol K9P.