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-   -   moisture testing with a multimeter (http://www.diychatroom.com/f19/moisture-testing-multimeter-6725/)

ronhud 02-26-2007 05:30 AM

moisture testing with a multimeter
 
I think it should be possible to compare the dampness of different walls by using the resistance option on my multimeter. When the leads are not touching anything the digital screen reads 1. As I test various walls I get readings between 200 and 1800. Intuitively it seems that 200 is wetter than 1800 - am I right?

concretemasonry 02-26-2007 06:53 AM

You may get the relative differences (wetter, dryer) of 2 walls made of the same materials IF they have been stabilized(moisture-wise) for a few days or weeks.

You can fool yourself very easily since you mat be dealing with only one layer (like the paper on gypsum board) and not the entire material.

What you are getting as far as results is a little better than a guess if it is for something important.

There are good dedicated meters for specific purposes and materials. My set up is about $600.

ronhud 02-26-2007 07:18 AM

moisture testing with a multimeter
 
ConcreteMasonry - thanks for the reply. I should have been more specific. The situation is that I have a series of small cellars and one corner of one of them seems to precipitate a lot of condensation. I thought of testing the comparitive dampness of the walls ( bare brick) to get some idea of where the moisture is coming from. 80% of the cellar area is dry so it appears that there is some local source of the moisture. I appreciate that this terribly unscientific.

Ron

concretemasonry 02-26-2007 07:31 AM

moisture testing with a multimeter
 
Condensation is dependant on the moisture content and the temperature of the material that the water may condense on.

I think you are looking for something other than condensation.

elementx440 02-26-2007 07:48 PM

To answer your original question, since water is more conductive than no water,

low ohm number = lower resistance = more water

though what you are actually measuring is debatable, as said above.

joasis 02-27-2007 06:39 AM

The impurity of water will affect the resistance value. Pure water will have infinite resistance, since it will not conduct electricity. Salt water readly conducts, as will hard water. So without knowing the value of the medium (water, moisture), you would have no comparitive value to base a test.

I use a moisture meter to check rough sawn lumber for MC....but that is a dedicated use, and it requires a standard of testing for accuracy.


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