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Old 01-15-2006, 08:27 AM   #1
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Lightbulb Inner shell condensation!

Jim and Susan, I've finally got my computer back up and running. How does "Inner skin condensation" sound for a new thread? I'm working on some 3D drawings of ideas on solving the problem. The more members that look at this problem and suggest ideas, the better the possibilities for a solution. We are fighting basic physics and nature here, so the results should be interesting.
I am going to go ahead and start a thread even though I don't have my ideas down yet. To see what comes up.
Don
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Old 01-15-2006, 08:34 AM   #2
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Okay, here's an idea:

I didn't say it was practical, but it would significantly help.
Remove the inner shell, and install sheet cork on the inner shell between the skins. This will minimize contact between the interior and exterior, provide some slight additional insulation, and help make the interior quieter. If the inner shell doesn't directly contact the ribs, or anything attached to the outside of the coach, it will redue the condensation. I don't know how well it would hold up to the motion of the trailer, but if you are feeling masochistic, it would be worth a try.
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Old 01-15-2006, 09:18 AM   #3
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I doubt that it is possible to entirely prevent inner shell condensation.
I think the best way to minimize the effects of it is to provide adequate ventilation.
My plan for my 1963 Overlander is to drill 2in holes towards the bottom of the skin, behind the furniture. Then put insect screen over the holes.
This way the hollow space has at least some way of ventilation, effectively speeding up the drying time. I am not certain how well this plan would work if the wall is stuffed full of fiberglass insulation batting, but mine are insulated with reflectix bubble foil, allowing plenty of air circulation.
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Old 01-15-2006, 07:48 PM   #4
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I think Uwe is exactly right here. You can't stop all of the water from getting in. You can reseal all the old Vulkem, replace all the weather stipping around the doors and windows and so on. But water (or water vapor) is going to get in. A couple of places that are hard to manage include the hole in the floor that feeds fresh air to the fridge, the fresh air inlet for the furnace and even the tail light assembly. All of these places allow water vapor in.

One thing I have noticed is that water vapor seems to condense at the top the camper. By this I mean on the inside, down the center of the of the ceiling. Now, my camper is still gutted so that it is open to the outside air which allows a bunch of moisture in. But, the other thing I noticed is that the stain patterns on the ceiling indicate that this has been going on for a while (long before I acquired the trailer).

So, how to combat water/water vapor inside the camper? Do the things listed above. Do the things that others have suggested. Run a dehumidifier in there all the time.

In my camper, water was the cause of the greatest damage everywhere. The early '70's trailers have a design flaw that allows water to literally pour into the belly pan. The belly pan can literally fill up with water. I can mitigate that some (actually, a lot) by redesigning the way the belly pan attaches when it is all put back together. But water/vapor will still be there.

The walls are almost the same way. Water vapor will be present inside the trailer. The normal cool down at night, warm up in sunlight cycle will cause water to condense out between the walls. I suspect this has much to do with rusted steel bolts and screws and at least some of the floor rot around the perimeter.

So, get to the point, right? Air needs to circulate from the bottom of the wall to the top, right? "Weep" holes at the bottom of the walls help, but if you assume the warm, moist air must rise, where does it go? How do you allow it to escape at the top? That's the $64k question.

Where does it go from here? Ok, Dudes and Dudettes, you got the ball.

Jim
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Old 01-15-2006, 08:46 PM   #5
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Hmmm...How about a series of small vents, that only vent into the outer skin along the top of the roof, with a cap that has a lip around it to keep out rain water? Kind of like the vents into my attic. They only vent the area between the ceiling and the roof. It's an idea, probably no worse than others have come up with, and similar to what I have seen on SOB's to keep moisture out of the 'tween walls area.
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Old 01-15-2006, 09:06 PM   #6
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Water vapor inside Airstreams during the winter

I got the idea from some of your posts that you think air coming in from the outside increases water vapor in the inside of the trailer. It is just the opposite. Cold 50% relative humidity air comes into the trailer from outside and, because the capacity of the air to hold humidity doubles with every 15 degrees rise in air temperature, this now warm dry air actually lowers the overall humidity in the trailer. If you have condensation on the walls of the trailer it because the walls are cold below the dew point temperature of the air in the trailer. Much like dew developing on the outside of a cold glass of beer. If you want to dry the trailer out, open the vents on the roof and let some of the hot moist air out and replace it with new air from the outside.

The excess moisture given off by people in the trailer is the largest cause of moisture gain. If you have a puddle of water in the belly pan, some of that might come up thru the floor. Water in the john and shower water, as well as boiling water for cooking, do not help either. If you would insulate both windows and walls better, that might also help keeping the moisture from condensing. That is why you have storm windows on all houses in the north. A dehumidifier (with a compressor on it) will condense some of the moisture out on its cold coils. Not a bad idea if you have alot of electricity. I keep one running in my basement during the summer.
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Old 01-15-2006, 09:26 PM   #7
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Dwight, unfortunately in this instance, the atmosphere here in the south where we live is saturated most of the days of the year. We have an old joke that goes "you measure it by the quart" and can "cut it with a knife in the sultry days of July".

The ultimate point here is that there is moisture (here in the deep south, a lot of it) in the air all of the time. AND, you can't keep it out of the camper. So, how to wick it out of the camper on an everyday basis. I'm not concerned so much with the few days a month the trailer is being used for its intended purpose, I'm more concered with the time it's siting in the backyard and doing nothing but waiting for the next road trip.

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Old 01-15-2006, 09:32 PM   #8
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Something we found in our Argosy that worked with limited success, but could wind up being cost-prohibitive, is setting out containers of Damp-Rid. I put in a new one every couple of weeks, they were always saturated when I changed them. It had to help, but I don't know how much (I didn't compare using it versus not).
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Old 01-15-2006, 09:37 PM   #9
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Quote:
Originally Posted by overlander63
Something we found in our Argosy that worked with limited success, but could wind up being cost-prohibitive, is setting out containers of Damp-Rid. I put in a new one every couple of weeks, they were always saturated when I changed them. It had to help, but I don't know how much (I didn't compare using it versus not).
Saw that stuff at the local RV dealer yesterday. It was kinda expensive, but then so is running a dehumidifier 24/7/365.

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Old 01-15-2006, 09:43 PM   #10
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moisture during storage

Jim-

We used to store the boat all winter with a 40 watt light bulb plugged in. You can reduce power costs if you are nearby and run it only during the times when the relative humidity is high. It gave just enough heat to keep the condensation and mold away.

This was in New England, so I have no clue whether it would work down south. It's less than one kwh per day -- hopefully less than 10 cents per day when you run it.


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Old 01-15-2006, 10:18 PM   #11
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I don't think that the corrosion is humidity related so much as it is a function of humidity and temperature differential in combination.
Someone mentioned the condensation on a cold beer - bingo!
The trailer sitting outside, same temp inside as outside, maybe a few windows cracked open, in addition to a roof vent for circulation should keep things under control.
I believe the trouble starts when one either heats the trailer, or cools the trailer substantially, to create an appreciable difference in temperature between the inside and outside.
I also believe that much condensation is caused by human habitation. Our breath is very moist...
Again, humidity or not, somehow I tend to think that ventilation is key.
Think how quickly a car window defogs when you open a wind wing, or crack a window open a bit while driving.
Remember, we're looking for condensation between walls, not general interior moisture.
I could be wrong, since my climate in SoCal is relatively dry and warm for the most part, and my experience with high humidity and it's causes are limited. A little fog by the beach and a few days of rain a year is about it for us.
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Old 01-15-2006, 10:53 PM   #12
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Don -
Your post is timely. I leave Wednesday for 4 nights camped in the Hoh Rainforest on the Olympic Peninsula in Washington. Photo from January '05 is attached. In nearby (substantially drier) Forks, WA, 18" of rain has fallen in the first 13 days of '06.
On this annual fishing trip, condensation gets serious. This year I've "pretreated" by running 2 electric heaters for 72 hours (temp inside the trailer tonight 58 degrees) and a floor fan 2 hours a day with roof vents partially opened. I hope to start off with a dry interior.
Once there, I'll have 110 volts only at night when the generator is running. Does the Suburban furnace contribute any interior moisture? Should I supplement with my two small 110 volt heaters? Suggestions welcome!
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Old 01-16-2006, 01:26 AM   #13
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Here is what got me started

Uwe, I believe you are on the right track when you mentioned the beer can analogy. About 3 weeks ago I had the following experience. The temp around here had been unusually cold. 18 to 20 degrees at night and maybe 32+ in the day. It had stayed that way for 3 weeks. Then within a couple of hours a warm front moved in and the temp went up between 40 and 55 degrees with heavy rain. Anything that was metal had become cold soaked . Within 30 minutes the inside of my shop looked like someone had turned a shower on. Everything was soaking wet. As soon as the air began to circulate and the temp of things equalized things dryed out. What I am looking at is creating an area of air circulation between the outside skin and the middle layer of bubble insulation. If I can create a convection current, I won't eliminate nature. But maybe I can help to dry the space out a little faster. I'm working on some drawings which I hope to submit them for everyones opinion in a couple of days. Thanks to everyone keep the ideas and comments coming.
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Old 01-16-2006, 07:09 AM   #14
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Interior moisture and condensation

Easy one first. No - Suburban furnace does not add to moisture in the trailer. The combustion air is completely separate from the air circulating in the trailer. Adding heat to cool moist air dryes it out, so heating the trailer up will lessen relative moisture and condensation. Catalytic heaters or stove add moisture.

The answers to how to reduce condensation at minimal expense in the widely varing weather conditions in the US are as variable as the weather. The old joke may apply. "If you want the air in the Airstream to be warm and dry, tow it to Southern Arizona".

No matter where you are located, an electrical dehumidifier is the best way to most effectively dry out a humid closed container. The Dry-it chemical approach is cost effective for only very small confinded sealed spaces.

Snowbirds that leave their mobile homes in Florida when they migrate north for the summer always leave their dehumidifiers or air conditioners on. It is the only way to prevent the units from developing mold because of the high humidity in Florida. The same should apply anywhere it is always humid like the Hoy rainforest, Gulf coast, etc.
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