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Old 05-22-2019, 07:57 PM   #1
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Mystery moisture, or, why is my wall wet? How to dry drywall?


When I took down the drywall in a room, I discovered moisture issues - some of the drywall is damp. For the exterior walls, this is related to soil in direct contact with brick and clogged weepholes (discussed in another thread). But on an interior wall, there is also moisture, and I'm trying to figure out the source.

In the following pic (pic is taken inside an attached garage), you can see mold (I have sprayed this down with mold control spray).


Using a moisture meter, I traced back some of the highest levels of moisture in the drywall to the dryer duct - the connection wasn't airtight and it was blowing humid air inside the wall. So I replaced that connection.

Following pic shows the drywall that was removed from the wall in the earlier pic. This is how I confirmed the source of moisture was the dryer duct (hole in the drywall is for the ducting).


I replaced the dryer vent connection a week ago. But the drywall next to this is still damp - 100% on the meter, while the drywall where you can see the mold is in the range 0-3% (though as I recall, that drywall never read 100%; I guess the leak in the duct blew the humid air against the garage drywall, but not against the laundry room drywall, so the latter got damp, as evidenced by mold, but not soaked).

Damp stud bays:


I labeled the damp stud bays A, B, C, and D, which you can hopefully see in the above pic. A is the stud bay with the cut lines in it. B is the stud bay to the left of that, and so on.

Almost all of A up to the height of the cut line is showing 100% on the meter (except for the top left corner, which is a little lower). If we extend the cut line to stud bays B, C, and D, that's the top of the range I'm measuring. So in B, the top (by the imaginary extension of the cut line) reads 0% on the moisture meter, but if measure a few inches lower, it's 100% and that's the same to the very bottom. In C, the 100% boundary is a fewer inches lower than B, and extends all the way to the bottom. In D, only the bottom few inches read 100% (above that is in the 0-3% range), and the very left portion of that stud bay is 0% even at the bottom.

I've had the window in the room behind this drywall open for the last 3 days (and the drywall in the room has been removed up to the ceiling - so there is nothing but air between this damp drywall and the window).

So either drywall takes a really long time to dry or there is another source of moisture. But as I said, the other side of those marked studbays is opened and there is no piping there and the signs of moisture start only a couple of feet above the ground. So if there is another source of moisture, it would have to be the concrete that this framing sits on.

I'm hoping the answer is that drywall takes a very long time to dry. I was planning on testing this by using a heat gun to dry off a ~2-3" perimeter around the edge of the drywall marked "A", and then see if moisture returns, and where it returns (i.e., does it return to the very bottom first). But I'd figure I'd post here since some of you guys probably have some experience with wet drywall and waiting for it to dry.
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Old 05-22-2019, 10:28 PM   #2
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Re: Mystery moisture, or, why is my wall wet? How to dry drywall?


Forgot to mention, all of the drywall with mold and/or moisture is going to be replaced. I just want to be certain I have the moisture issue resolved before replacing, as I'd hate to install new drywall only for it to become wet.
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Old 05-22-2019, 11:20 PM   #3
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Re: Mystery moisture, or, why is my wall wet? How to dry drywall?


Good catch. I think a leak in that duct could have done all that we see.

Scrub the wood with a solution of detergent and bleach. Treating them with copper would not hurt either.
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Old 05-23-2019, 05:37 AM   #4
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Re: Mystery moisture, or, why is my wall wet? How to dry drywall?


Is that room a conditioned room? If itís cold in there and youíve got the warm moist air going through the vent itís going to make a lot of water. The way the pipe droops would aggravate the situation. A solid pipe would be a little more work but less chance for water accumulating in the dryer vent.
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Old 05-23-2019, 07:06 AM   #5
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Re: Mystery moisture, or, why is my wall wet? How to dry drywall?


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Is that room a conditioned room? If it’s cold in there and you’ve got the warm moist air going through the vent it’s going to make a lot of water. The way the pipe droops would aggravate the situation. A solid pipe would be a little more work but less chance for water accumulating in the dryer vent.
After I resolve this moisture issue and replace the drywall, I'll be redoing the ducting to use all semi-rigid or even solid pipe instead of the flex hose you see.

The room in the pics is an unconditioned attached garage. Even with the flex hose, there is no water in the ducting - further to the left of the pics, where the flex hose reaches the exterior wall vent, the hose slopes down a little bit, so the area where condensation inside the hose is most likely is sloped down toward the exterior wall vent.
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Old 05-24-2019, 04:57 PM   #6
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Re: Mystery moisture, or, why is my wall wet? How to dry drywall?


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So either drywall takes a really long time to dry or there is another source of moisture. But as I said, the other side of those marked studbays is opened and there is no piping there and the signs of moisture start only a couple of feet above the ground. So if there is another source of moisture, it would have to be the concrete that this framing sits on.

I'm hoping the answer is that drywall takes a very long time to dry. I was planning on testing this by using a heat gun to dry off a ~2-3" perimeter around the edge of the drywall marked "A", and then see if moisture returns, and where it returns (i.e., does it return to the very bottom first). But I'd figure I'd post here since some of you guys probably have some experience with wet drywall and waiting for it to dry.
So this test was a failure. I spent a few minutes using a heat gun on a patch of the damp drywall, hitting it from both sides. Still reads 100% on the moisture meter. So either drywall takes a really long time to dry, or the patch I'm hitting is simply absorbing moisture from the adjacent areas.
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Old 05-24-2019, 05:02 PM   #7
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Re: Mystery moisture, or, why is my wall wet? How to dry drywall?


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So this test was a failure. I spent a few minutes using a heat gun on a patch of the damp drywall, hitting it from both sides. Still reads 100% on the moisture meter. So either drywall takes a really long time to dry, or the patch I'm hitting is simply absorbing moisture from the adjacent areas.
The factory drys drywall with over 600 degrees and leave some amount in to provide some fire proofing. It makes steam when exposed to fire.
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Old 05-24-2019, 05:29 PM   #8
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Re: Mystery moisture, or, why is my wall wet? How to dry drywall?


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The factory drys drywall with over 600 degrees and leave some amount in to provide some fire proofing. It makes steam when exposed to fire.
Interesting. So are people actually drying drywall after leaks and floods - all the info I'm seeing on the internet is along the lines of set up a fan and maybe a dehumidifier. And that's supposed to dry drywall that's part of an intact wall (i.e., drywall on both sides of stud bay and possibly insulation in the stud bay)?

I've had this one drywall (no drywall on other side of studs, no insulation) stay damp for a week. So I guess when people are recovering from a flood or leak and not replacing drywall, they are just looking to get the drywall from soaking wet to damp?
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Old 05-24-2019, 05:39 PM   #9
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Re: Mystery moisture, or, why is my wall wet? How to dry drywall?


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Interesting. So are people actually drying drywall after leaks and floods - all the info I'm seeing on the internet is along the lines of set up a fan and maybe a dehumidifier. And that's supposed to dry drywall that's part of an intact wall (i.e., drywall on both sides of stud bay and possibly insulation in the stud bay)?

I've had this one drywall (no drywall on other side of studs, no insulation) stay damp for a week. So I guess when people are recovering from a flood or leak and not replacing drywall, they are just looking to get the drywall from soaking wet to damp?
Drywall take some time to get wet too, I have dried it when it was caught the same day by drilling holes between each bay and letting it dry for months. With yours I would just replace it, the mold spores are there in abundance already all they need is a chance to get started.
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Old 05-24-2019, 05:44 PM   #10
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Re: Mystery moisture, or, why is my wall wet? How to dry drywall?


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Drywall take some time to get wet too, I have dried it when it was caught the same day by drilling holes between each bay and letting it dry for months. With yours I would just replace it, the mold spores are there in abundance already all they need is a chance to get started.
For sure I'm going to replace it. I just want to be sure there isn't another source of moisture that hasn't been addressed. So I was thinking of drying off a part of this drywall and seeing if moisture returns. But I guess this won't work because any part that I apply heat to to dry will just absorb moisture from adjacent drywall.

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