So, a couple of weeks ago I bought a dehumidifier for our unfinished
basement - the walls are poured concrete. After a couple of days I
noticed a horizontal dark line about two inches wide stretching along
one of the walls. It starts in a corner and just ends a few feet along
the wall. It is under the level of the soil outside - the ground
outside is well graded away from the house, and it hasn't
rained much recently. The line does not feel wet to the touch. I assume
this has something to do with the humidity in the basement decreasing
relative to the moisture in the ground outside/in the walls?

schrieb:

So, a couple of weeks ago I bought a dehumidifier for our unfinished
basement - the walls are poured concrete. After a couple of days I
noticed a horizontal dark line about two inches wide stretching along
one of the walls. It starts in a corner and just ends a few feet along
the wall. It is under the level of the soil outside - the ground
outside is well graded away from the house, and it hasn't
rained much recently. The line does not feel wet to the touch. I assume
this has something to do with the humidity in the basement decreasing
relative to the moisture in the ground outside/in the walls?

Hello,

If the dark line - doesn't sound right to me - does not feel wet to the
touch, it might be because of the dehumifier in use, that takes it off
the surface.
With a simple DVM (and its Ohm reading) measuring against ground you
might find out if there is contact. This may indicate that you have an
intrusion.
Additionaly it may be easy to take photos and mail them to me so I can
have a closer look.

For more on how it could look like in a later stage and if nothing is
done/corrected in the early stage, please check out: www.drytronic.com
for more details and also on the cure of such.

By the way: Did you clean the dehumifiers filters at least every day?
Otherwise it could whirle around spores and this is no fun at all.
My mother cought pneumonia and had a rough time to survive.
That was the reason for me to develop something new to get rid of the
wet walls and floor and that dehumifier as a pseudo cure for such
reasons !