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Community and Q&A

Moisture mitigation system

JustBeingMe2 | Posted in General Questions on

I just had a French drain installed even though I don’t have water problem in my basement.  I have an small area of the basement floor that is damp and I do have efflorescence in other areas of the floor.  I believe the problem I have is that the humidity is high so the French drain is useless because I’m still running a dehumidifier 24/7.  Now the contractor wants to install a moisture mitigation system by using a fan and venting it through the French drain.  I would like to know if that is really going to solve my problem?

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  1. Jon R | | #1

    I assume the problem is dehumidifier run-time? Both water from below and air exchange can cause this.

    1. JustBeingMe2 | | #3

      If I don't have the dehumidifier working, there is definitely a musty odor in the basement.

  2. Walter Ahlgrim | | #2

    Tell us about your house and how you expect to use your basement.

    There was a time when basements had dirt floors no one expected it to be a place to spend any amount of time, today we have very different expectations.

    If you goal is to keep water from coming thru the walls you need to work on the outside of the walls with working drains and thick coatings. Not ease or cheap.


  3. JustBeingMe2 | | #4

    My basement is not finished but I keep clothes, furniture, etc. It's very organized. So, in the area where I have moisture on the floor, the oil tank used to be there (above ground). I did have dirt at one time but my cats thought it was a litter box so I had a layer of concrete put there. Could part of the problem be that the concrete is not thick enough?

    When I spoke to the contractor and told him he did not solve the problem, he then said he would apply Kosters NB1 Gray to that area. Fortuntely, when I called the manufacturer, they advised me that it was for walls only. They suggested putting Vap1 2000 instead.

    Now the contractor comes back and states he wants to do a moisture migration system (in that one spot at his cost), but once again, I have another expense because I need to put an electrical outlet there for the fan. The sump pump area is across the room, so how is this going to work?



  4. Walter Ahlgrim | | #5

    Since it had a dirt floor we can assume it was built before 1950 without exterior foundation drains. Does your basement have stone walls?

    I doubt the thickness of the concrete is a problem. I do wonder if a vapor barrier and a few inches of rock had been installed under the concrete.

    I am not sure what a “moisture migration system” is. My Google search comes up with lots of epoxy floor paint nothing electric on the first page. Did he give you any idea what this system is?

    Is there water in the pit?
    How often and for how long does the pump run?


    1. JustBeingMe2 | | #8

      Hi Walta,

      It is similar to a radon rediation system. Cinder block walls and concrete floor.

  5. Expert Member
    Peter Engle | | #6

    It sounds like he is proposing a vacuum system connected to the French drains, similar to a radon remediation system. A lot of people install radon remediation systems and find that their basement get much dryer as a side benefit and some contractors are now installing them for that reason alone. If the French drains and sump pit are fully sealed, this approach can somewhat reduce the moisture vapor coming up into the air. But that would not be my first choice. Neither would the French drains. It sounds like the concrete wasn't placed over a plastic vapor retarder, and soil moisture is simply wicking up through the concrete. if that's the case, it won't hurt anything and a dehumidifier will remove the moisture at a reasonable cost. Topside vapor barrier paints (like the Vap1 2000) can help, if the floor is very clean when they are applied. If not, they will blister and pop off the floor. If it's all being done at the contractor's expense, it can't hurt. Just make sure the fan/suction system isn't pulling air from the basement. That can backdraft appliances and increase damp outside air infiltration.

    1. JustBeingMe2 | | #7

      There is no water except for some condensation in the sump. He is willing to do one thing, not both. I'm still concerned with the fan/suction system since it's on the other side of the basement. Will this system (similar to radon remediation systems) take care of the whole basement floor? How does it actually work, how is it installed and how does one know about the backdraft? Would you suggest I have him do the VAP12000 in that small area (which is not very clean because when they did the French drains, they had dirt on it)?

      Thank you

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