Moisture Meter - Confusion

Warning - this maybe a dumb question :slight_smile:

I was at my neighbour’s house yesterday – he wanted an opinion on something. Our discussion led me to use my moisture meter on his bathroom floor (ceramic tiles) located in the basement. The meter showed the highest level of moisture presence throughout the floor. I then used my meter on his laminated flooring (still in the basement) and the meter still confirmed presence of water throughout the basement floor which did not make any sense.

Do you know why this may be happening?

The RH in the basement was approx 55-60% but I don’t think RH has anything to do with this. The RH on the main floor was 45%. Is there a possibility that the meter was picking up moisture off the ground/soil below the concrete floor but then the meter only picks up signs of moisture/water 3/4 inch deep. I thought maybe there is something wrong with my meter and used it on the main floor but everything was bone dry.

I used my IR camera and the bathroom floor seemed just fine. The ceramic tiles were not glazed so I know that the IR camera was giving me the correct results.

Thank you

It’s not the meter, read the manual.

At what temperature?


What is the temp of the floor?

A thermal camera is not a moisture meter.
So what results are you considering correct?

If you don’t know the dew point, what temperature on the thermal camera would be a concern?

The air temp was approx. 70F

Sorry, dont have that info.

I know David, why would you say that? :slight_smile:

I am going with my IR camera results. I would like to know why the meter was detecting moisture?

I think the dew point was 50F.

Already did, no hints there.

70F @ 60% RH = 55.5 F DP

Is it not feasible that the slab would be at this temperature (year round)?

What “Corrected Temperature” did your IR register?

Which floor in basement was detecting the most moisture?

In Missouri, if we have 60% humidity in a basement in late fall, we are looking for the reason why.

He can’t determine that unless he converts the readings from wood to tile.


My moisture meter does not have an option to switch between different materials. Plus, why would it give me a different result on the main floor (same material)?

BTW, there was a big fish tank in the basement.

I just need to know the readings. Conversion in this scenario is not really needed. The high humidity would throw a meter that had different scales off because of the adsorption rate of the different materials tested. Comparative readings should only be used when high humidity is present. This link explains it better .

most obvious but unseen would be differing underlayment, adhesive/setting, padding, patching material, leveling compounds…

been on new construction where an oops occurred with a fairly large floor penetration
the builder used a metal plate to cover the hole and covered with pad & carpet
what would that do to your mm readings? seriously doubt ir would detect anything in conditioned space as it would in the list above

I was inspecting a wall I thought had moisture present. The moisture meter went off like crazy around an interior door at a church. Used my thermal imager and nothing showed up. I realized the metel jamb around the door was causing it to go off. Perhaps like the above poster it was something metallic perhaps it was rebar, just a thought.

The “manual” for my meter is a little piece of paper about 3"x5".

Part of the problem is that moisture meters don’t read moisture levels, they read variations in electrical conductivity, which varies with different materials and with variations in chemical composition.

Testing floor tile laid over concrete in basements, my Protimeter always reads high. I check around to try to develop a baseline for comparison, but mainly in looking for moisture in basement floors, I use my eyes first. If the basement is finished I try to find a place where I can see the base of the foundation walls, and I tap floor tile near areas likely to leak, like near the toilet or where pipes penetrate the slab.

For IR, you need a strong temperature differential, which you may not have between a basement slab and the subgrade.

Good link, James!

plain and simple never trust level readings but compare with known dry areas.
The reason I carry two as well.