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kfergiez 02-26-2019 11:33 AM

Underbelly membrane leak... WHILE winterized
So I've got a stumper.

We went on a fantastic winter trip to the ski hill with the trailer winterized. When we got home, I noticed 2-3 spots where my underbelly membrane was dripping, and I noticed that water was above it making the insulation wet.

Our trailer is winterized, so the only way that I can figure water got up there is from road spray. I cannot find any spot where water could get up INSIDE from underneath. Any ideas? How do I dry it out? How do I make sure it doesn't happen again?

chaps2018 02-26-2019 11:36 AM

I recently had a similar situation—it was the temperature differential of 25deg overnight. The sudden warmth made the entire trailer sweat. Coroplast underbelly, wheels, etc were dripping wet.

kfergiez 02-26-2019 11:39 AM


Originally Posted by chaps2018 (Post 2034384)
I recently had a similar situation—it was the temperature differential of 25deg overnight. The sudden warmth made the entire trailer sweat. Coroplast underbelly, wheels, etc were dripping wet.

Of course we experience that on the walls and windows inside the trailer from 5 people breathing and whatnot, but I never really thought that would happen to the underbelly.

Come to think of it, the areas where it's the MOST wet is by the door, and underneath the bathtub where theres a cutout for a drain.

How did you dry it out?

chaps2018 02-26-2019 11:59 AM

I apologize if I wasn’t clear—it was the temperature differential from the day before. 40deg Tuesday. 65deg by wed morning. Everything on the inside of the rig was dry it was the outside that was sweating walls underbelly wheels etc.

That said, I just noticed the OP mentioned his insulation was wet in the underbelly that would imply a lot of moisture on the inside which I wouldn’t think normal sweating would do.

kfergiez 02-26-2019 12:02 PM


Bummer. Yes, the moisture is INSIDE the membrane against the insulation.

chaps2018 02-26-2019 01:15 PM

Underbelly membrane leak... WHILE winterized
Ok so just checking. When u winterized the lines, and tanks were all drained? Including fresh water tank?

kfergiez 02-26-2019 01:17 PM

Yes. We winterized by completely emptying the freshwater tank, the water heater, and blowing out the water lines with air.

That and all of our tanks are below the membrane and open to the air. No coroplast.

chaps2018 02-26-2019 01:33 PM

Thanks for the clarification on coroplast.

Have you cut the membrane open yet? (Ie, How do you know the insulation is wet)

Is the membrane cloth or woven plastic?

If it were mine I would order scrimshield tape (amazon) for the resealing and get busy cutting it open to see how far the wet insulation goes. Start small keeping in mind how you will plan to reseal.

The repair tape is very sticky and you have to apply it as the backing is removed else it sticks to itself and won’t separate.

I have used fans, pulled insulation out etc to get it to dry. Of course it all depends on your specific model and construction methods.

kfergiez 02-26-2019 02:02 PM

It's a woven membrane, and I found out that it was wet because I noticed some dripping behind the tire the day after we came home from our trip (and the wet road stuff should have dripped of by then).

It was near the tub, so I unscrewed the access panel from below the tub, and stuck my hand down beneath the floor and things are wet.

I poked a small hole in the membrane, and while water didn't come POURING out it certainly dripped more.

I can cut the membrane open and reseal, but the more pressing matter is how do I find where it's coming from?

The only assumption that I have is that it's from road spray. But again... where?

kfergiez 02-27-2019 01:18 PM

I THINK I've found the issue, and it's not very preventable.

I've looked around in all the areas where I'm finding moisture above the membrane, and they are in 3 areas.

1) The front door
2) In a corner by our bed
3) Just below the bathtub.

I then thought, what makes these areas prone to be a moisture trap? Well, the tub has water... duh. BUT our rig is winterized, so that doesn't make sense. The front door is where we enter and exit with snowy boots (we try to minimize this and knock off as much snow as we can, and pile our boots in the bathtub). And beside our bed? There's nothing there.

There is NO rhyme or reason for road spray to get up in there because the spot by the door and our bed is IN FRONT of the wheels, and there are sections in front of them that get way more spray from the tow vehicle and those spots are dry. The bathtub is behind the wheels, but theres a section between the tub and the wheels that is bone dry so that doesn't make sense either.

THEN I finally think I found a reason. I BELIEVE it has everything to do with the excess condensation, and boot snow. Even though we try to clean off our boots as best we can, some water will be by the door from boots, but there's a TON of condensation and frost that forms and runs down the door frame. Where does that water go? I'm thinking it gets into the seam between the wall and the floor then runs down from there.

Then the spot by the bed. We piled a couple of backpacks in that corner, and when I picked them up in the morning, it was so cold outside that ice had formed ON THE WALL behind our back packs. I'm not talking about frost, I'm talking a good solid layer of ice from condensation. Our backpacks acted like an insulating layer keeping cold down there. Where did that water go? Again, I'm thinking between the wall and the floor.

Finally, the bathtub. There is a hole cut into the floor below the drain to accommodate the plumbing and there's a gap in the insulation so you can see the membrane directly. That means the ONLY thing keeping the cold out is the tub shell which is going to gather condensation like crazy. Then it drips down directly onto the membrane.

These are my thoughts. Any criticism is welcome.

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