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Old 12-29-2015, 03:35 PM   #1
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Condensation between inner and outer Skylight

I have a 2001 Expedition, Diesel Pusher,36 foot.

The problem; I have thought that the skylight was leaking, have tried eternabond, didn't stick to the rubber roof, for what ever reason, even used the cleaner that was specified, but that isn't the problem.

Removed the Eterna bond and used two tubes of dicor, really caulked that thing. It is a neoangled shower, and has an inner and outer skylight. Both are made of plastic. What I thought was a leak is actually condensation forming between the skylights and running down the inner skylight and staining the fuzzy ceiling. We have used Instagone to remove the stains.

Some of you guys who are much smarter than I please give me some ideas for stopping the condensation between these skylights.

I have thought of drilling holes in the inner skylight to allow air to circulate between the two surfaces, how many holes, how big?

I know I have to get air circulating between the surfaces, has anyone else run into this problem and what was your solution?

By the way, leaving the inner cover off is not possible without some major reconstruction in the shower as the inner cover also hides the raw foam and wood that shows around the shower ceiling if left off.


MGySgt USMC(R) 1961-1991
2001 Fleetwood Expedition
2013 Jeep Wrangler Sierra Toad
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Old 12-29-2015, 04:44 PM   #2
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Unfortunately, the moisture between the two layers will never disappear on its own. I would look for a roof to park under, or a weather window of a few clear days. Remove the skylight and allow thorough drying of the roof layers sandwiched between the rubber outer layer and the inside finish layer of your roof materials. This can take some time depending on how damp the material is and ambient drying conditions.

When installing skylight, bed it in butyl putty tape. Then cover perimeter with Dicor self leveling or Eternabond Tape. If your skylight is original equipment, it has deteriorated due to UV. Strongly consider replacing it at this time. All the best.

George R. - Fulltiming since January '03
2007 Newmar Mountain Aire 3991
2012 Chevy Malibu LT1
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Old 12-30-2015, 05:30 AM   #3
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Thanks George, I know if I drill some holes in the inner skylight to allow air circulation between the to layers it might help, also give the condensation a way to escape without soaking back into the ceiling material.

I have removed the inner skylight to allow drying and placed a oil filled heater near the shower to give it some heat to help in the drying. Don't have a place to park her under a roof, been thinking of building a pole barn over the parking pad, may do that.
Thanks again
MGySgt USMC(R) 1961-1991
2001 Fleetwood Expedition
2013 Jeep Wrangler Sierra Toad
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Old 12-30-2015, 05:58 AM   #4
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If you drill holes in the inner skylight to get rid of condensation, you haven't solved the problem, and may create a new one.

First: the problem you haven't solved is how the water got in there in the first place. Gruelens, above, gave you the answer on solving the water intrusion problem. Messy, but the only permanent fix.

2nd: if you drill the holes to allow the moisture to get out, you need to supply some way of encouraging it to do so! If you have a compressor with DRY AIR (which pretty much means either Arizona, or having a refrigerated air dryer installed on the compressor, you can get the moisture out by running air hose into one hole, and allowing it come come out of another hole. Size wouldn't particularly matter, just airflow. However, that still doesn't prevent the water from getting in the same way it got in to begin with, (see "First" above). The OTHER issue is that you need to SEAL the holes up again, or water vapor from showers will get in there, condense on the outer (probably colder) plastic layer, and you'll be back where you started from, only probably worse.

Unfortunately, the only way to really SOLVE the problem and to remove, either rebed, or replace the existing skylight. Good luck in whatever you decide.
Scot & Laura Kellersberger
Newmar 4 wheel drive Dutch Star 3891, 2005 GMC Canyon. Demco Tow Bar & Baseplate U.S.Army (ret)
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Old 12-30-2015, 06:58 AM   #5
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You mention that you had removed and reinstalled the inner skylight. Is it sealed properly?

Have you considered the possibility that inside warm humid air is leaking past the inner skylight, contacting the cold outer skylight, causing condensation?

Jim & Kate
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Canada, eh?
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Old 12-30-2015, 08:50 AM   #6
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Drilling holes in the bottom skylight could allow steam from the shower to enter into those holes, which of course would just cause more condensation to form.
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Old 12-31-2015, 04:21 PM   #7
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Yeah, scrapped the idea of drilling holes, yes, warm air is getting into the space between the two skylights, inner and outer, causing the condensation problem. I have noted that the foam has voids that run back in towards the interior and exterior of the coach, this is in the ceiling.
I am now thinking that the voids are allowing warm air to invade the area between the skylights causing the problem.
I think I will close the voids with expanding foam and that may take care of the problem. I'll try and take a couple of pictures so you can get an idea of the problem.
As far as sealing the bottom, lower skylight, no it just screws into the fuzzy ceiling, so the seal is far from air tight, that's the way it was designed.
Thanks for all the replies, wish someone with an Expedition had jumped in.
MGySgt USMC(R) 1961-1991
2001 Fleetwood Expedition
2013 Jeep Wrangler Sierra Toad
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Old 01-02-2016, 10:35 AM   #8
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As long as there is air between the two skylights, you will get moisture.
2006 Damon Daybreak 3272 w/F-53 @ V10
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Old 01-04-2016, 08:08 PM   #9
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We have a Newmar dp. I found that the inner cover was only attached with double sided tape. So we removed the plastic flange inside the shower and sealed the inner skylight to the flange with hot glue. Now we just need summer to drop in and we will remove the outer cover and dry the roof.
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Old 01-05-2016, 12:38 AM   #10
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Had that problem with one of our Dutch Stars. Newmar said to drill some holes in the inside edge. Used like a 1/8" drill and did something like 4 one each side. Never had an add'l problem.

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