Thread: Multimeter as a moisture detector?

If I set the probes at a fixed distance, is there a way of converting the resistance measured into a measurement for moisture content?

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Originally Posted by Tony Hipps

If I set the probes at a fixed distance, is there a way of converting the resistance measured into a measurement for moisture content?

Possibly, but with the time and expense to figure out what is what on what materials you would be far better off buying and using a moisture meter.

Originally Posted by Jerry Peck

Possibly, but with the time and expense to figure out what is what on what materials you would be far better off buying and using a moisture meter.

Ten - four

Good morning, Tony!

Although Jerry is probably right, the reality is that there is nothing wrong about your presumption, and the application of your idea perfectly valid.

During our building assessments for mould, moisture data from wooden structures, drywall and a variety of other materials are collected using a Tramex® PTM 6005 conductivity style moisture meter. Although the meter is a very commonly used “moisture meter,� contrary to common belief, the meter does not actually measure moisture; rather the meter measures electrical conductivity and (sort-of) translates that conductivity into (kind-of) general moisture equivalents (almost). But the meter is very limited, and the readings, like all other such “moisture� meters, is very much a guess.

For example, if the meter probe was placed in 100% distilled water, it would read less than 8% moisture. If a small amount of salt was placed in the water, the “moisture content� would steadily increase until approximately 43%; indicating moisture saturation. If we keep the salt solution stable and alter the temperature, the readings change.

Once we start plugging the pins into hard surfaces and pretend we are measuring moisture, the physics get even more complex.

Therefore, the moisture values given in any discussion on moisture content should be used with caution and within the limitations of the meter and parameters discussed. Using your multimeter, and interpreting the data based on your own experience (and perhaps using a Pal’s “moisture meter� for comparison would be just as valid as using a purchased moisture meter - and it would be one less piece of equipment to lug around.

Cheers!
CaoimhÃ*n P. Connell
Forensic Industrial Hygienist
Forensic Industrial Hygiene

(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)

AMDG

A thought occurred to me while reading Jerry's apt reply. I would recommend that you get a moisture meter without probes, even the short ones, since this can cause damage to surfaces that you probe. I have direct knowledge of a repaired ceiling a beneath bad shower floor where the patch fell out after the inspctor probed it, causing a goopy mess! The homeowner was not happy even when the Home Inspector explaned that he was just doing his job, checking a repaired ceiling beneath a cracked and old shower floor. In another case an issue was raised about lead paint dust being created. I use an old "Tramex" with pads that is truly "non-destructive" and is also good to check flat roofing without probings.

Originally Posted by CaoimhÃ*n P. Connell

Although Jerry is probably right, the reality is that there is nothing wrong about your presumption, and the application of your idea perfectly valid.

Although the meter is a very commonly used “moisture meter,� contrary to common belief, the meter does not actually measure moisture; rather the meter measures electrical conductivity and (sort-of) translates that conductivity into (kind-of) general moisture equivalents (almost).

CaoimhÃ*n,

That I know.

This "but with the time and expense to figure out what is what on what materials" was referring to was the calibration aspect.

By the time Tony make a jig to hold the multimeter leads in exactly the same location, and with the standard multimeter leads being somewhat large in diameter to start poking into walls, and then to buy/rent/borrow a moisture meter to use for calibration, and then the effort at calibration ...

I said "you would be far better off buying and using a moisture meter."

There are, in fact, some multimeters which come with moisture meter heads where all that calibration has been done for you, and the thicker multimeter probes replaced with moisture meter pins, but, again, that would mean buying something new.

My presumption was that Tony was looking for a way to use a multimeter he already owns as a moisture meter, based on that presumption ... it ain't worth the effort to do so.

Good morning, Jerry!

Your original post and meaning was clear, and I was agreeing with you. My blood coffee level is a little low, and so I may not have expresssed my thoughts clearly.

Evan:
Capacitance, resistance and conductivity al have the same limitations – just different errors. For example, relying on capacitance can result in elevated “moisture” readings when in close proximity to metal pipes, etc.

“In another case an issue was raised about lead paint dust being created.”

Not a significant issue.

Finally, even if one were really measuring moisture content, not all moisture content is the same. Moisture occurs in many distinct ways in materials, and, usually, the more common “moisture meters” are measuring bulk moisture, or available moisture. Actual moisture content or total moisture would not be measured.

Back in my lab maggot days, we measured bulk moisture content of materials in per cent at a specific temperature; and trace moisture in units of the pressure needed to remove the moisture (usually derived from the amount of heat needed to remove the moisture).

Cheers!
Caoimhín P. Connell
Forensic Industrial Hygienist
Forensic Industrial Hygiene

(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)

AMDG