Double Pane Windows Leak Repair

Repairs to double paned windows

My double paned windows, if they blow a seal, and I’m not talking about their personal lives, will accumulate moisture between the panes.
Here’s a picture of how bad it can be:

Each window in the bus, other then the front windshield and the bedroom rear window, has two double paned portions, one slides open and one is fixed. Then there is a bug screen. Every window of this type is double paned and are made with an aluminum channel between the panes that is covered with butyl rubber to seal them. The frames are all aluminum. Occasionally, leaks can develop that allow outside air to infiltrate the window in the area between the panes. If it carries moisture, it can condense on a pane, usually the inside pane. That makes the window difficult and sometimes impossible to see out of. I have three window panels that have developed leaks in their seals so this week, after nearly three years of ignoring the problem, I decided to do something about it.

The first window I tackled was the small window right next to the door, sort of a training window for me. It’s about 30” wide by 25” tall. First, I removed all the screws from the inside frame. Then with a little tugging, removed the inner frame and the screen. Then I gently pushed the window assembly outward. Since there was some silicon caulking along the right edge of the window on the outside, it didn’t fall to the ground. After it was loose, I went outside, cut the silicone and pulled it out of the frame. It would have helped to have a helper but everyone was busy that day. Back inside the rig, I began by taking the top rail off the window assembly. There are two screws on either end, first covered with butyl caulking and then a layer of duct tape. As well as a single screw holding the center rail. With those five screws removed, I then peeled off the foam sealer from the top rail and a few inches down each side rail. Then I draped it out of the way. This allowed me to remove the top rail and then lift out the window section with the leak. With the window out, I cleaned up everything, but I left any gobs of butyl to reuse. I also removed and cleaned the small plastic assemblies that have tiny plastic wheels in them that are suppose to make the window ‘roll’ along the lower sill. They stopped ‘rolling’ years ago and had worn down to a flat spot on the roller that would slide along the plastic sill cover. Since the windows open and close fine, especially when sprayed with silicone lubricant, I left these alone after cleaning because, ‘why fix something that isn’t broken’? And I expected it would be very difficult to find those little plastic wheels as repair parts.

Here’s a picture of one corner, after two screws and the tape have been removed. The foam seal is positioned out of the way, draped over the front of the window. After this is done, the top rail can be removed, after which the sliding portion of the window assembly can be removed. Since this window’s sliding section had the leak, I didn’t have to deal with removing the fixed portion of the window assembly:

After cleaning, I drilled three 5/32” holes along the top rail, about 6” apart, and centered between the panes. I chose to drill along the top rail and not the bottom rail because I did not water to somehow be wicked up from the bottom channel if condensation got down into the bottom channel of the window assembly. I didn’t drill into a side rail for different but similar reasons. The top of the window has an excellent waterproof cover and would tend to be warmer so I felt it would have less condensation in and near that rail, so less chance of creating a new problem. While I was working I tried to come up with a method of resealing the holes after I was finished getting the moisture out from between the panes. I could use silicon caulking to fill the holes but I didn’t know how the silicon and butyl rubber would react to each other and I didn’t want to create a new problem. Plus I didn’t know if this method would work the first time so I wanted to be able to open the holes again easily if it became necessary. I could use homemade soft rubber plugs but those seemed difficult to fashion from what I had on hand. I could use sheet metal screws but didn’t think they would seal well enough. What I settled on was just using duct tape to cover the holes since it’s water proof, makes a good seal, stays in place, doesn’t shrink, and won’t react with butyl rubber. It seemed the easiest to deal with, I could remove it easily, and it should last for years in the relatively protected place I was going to put it.

Here’s where the holes were drilled:

I worked carefully, because I didn’t want any drill tailings to fall between the glass plates. Then after drilling, I picked out or vacuumed any drilling debris I could find. It’s not much of a worry with this type of window because of the butyl rubber sealer used inside the window would stop things from dropping in there but I wanted to be sure. Then I used a sharp awl to pierce the butyl rubber. After that I spent several minutes with each hole using the awl or a drill bit to twist the soft and pliable butyl out of the hole.

Poking the awl down through the butyl seal:

The first window the butyl was nice and soft and cooperated. On the second window, I found it to be stiffer. Like it had lost some flexibility over the years. In any case, I was able to remove enough. When I could see a little daylight through the holes, I began to heat the window with a heat gun. I used the 630F setting because I was worried that if I used the 1,000F setting I might shatter the safety glass. I’m sure a standard hair dryer would work just as well. I started heating the window at the bottom and slowly worked up. Occasionally, I’d turn the frame around and heat the other glass. This slowly vaporized the water between the panes, and the three holes at the top allowed the moisture to escape. After the air between the panes was warm enough that I could see water on the surface vaporizing, I inserted an air pump (used to inflate tires) into the center hole, using a plastic tip that is usually provided with the pumps these days. This particular tip is generally used to inflate vinyl beach toys.
Here’s the equipment I used for this little project:

The moving air forced the moisture to vaporize rapidly. I could see it disappearing from the inside surfaces of the glass. The pump gauge registered 25 PSI while it pumped and I could feel a strong air flow out of the open holes on both sides of the center hole. After around 15 minutes of heating and blowing, the moisture seemed to be completely gone so I shut down the pump and immediately covered two of the holes with small ‘silicon’ crystal drying packs, like the type that come with a new watch or small electronic device. These would dry the air that would be sucked back between the panes as they cooled. I sealed the 3rd hole with a piece of closed cell foam since I was out of the little silicon packs.
The silicone moisture removing packets in place:

After 30 minutes of cooling time, I covered the holes with duct tape and then reinstalled the window in the frame, and then in the window opening.

After that, I moved onto the passenger window. It’s around twice the size of the smaller one I’d trained on and since I still didn’t have a helper, I used packing tape loosely taped from the outside of the window top to the RV sidewall. After removing all the inside screws and the inner frame members, I pushed a little on the frame from the inside and the entire frame popped loose. With the window assembly restrained by the packing tape, I went outside and with a borrowed ladder carefully removed it and brought it inside. This window was quite a bit heavier and I had a little bit of a struggle getting it safely down and inside the RV to work on.

Again the sliding portion of the assembly had the leak and lots of moisture between the panes, so completely covered with moisture that only the front half of the window was usable. So I followed the same routine with this slightly larger window (40” wide), removing the inside frame. Then drilling 3 holes along the top of the assembly, heating, and pressurizing. Took longer than the small window of course. After an hour or so of heating and pumping in 25 PSI air, it looked as though the moisture was gone so I followed the same procedure as with the smaller window; sealed, reassembled, and reinstalled just before nightfall.

With this window I should have had more patience and heated it longer because several hours after reinstalling, there seems to be a re-accumulation of moisture between the panes. The smaller window is still perfect. I will let the small amount of moisture between the panes go for now, it’s a pleasure to finally have a passenger window where I can see more than 50% of the view, and there is so much of the moisture gone it’s a 95% improvement. I have been living with it cloudy for 2 & ½ years, and the clear view is a welcome improvement. Someday when I’m bored I’ll remove it and do the process again.

(On edit: It’s now 3 years later and the smaller window is still clear. The larger window does show a small amount of condensation in the right lower section, not enough to affect driving, but I’ll redo that window next spring anyway.)

(On edit: It’s now 9 years later and the smaller window is still clear. The larger window occasionally shows some moisture if I’m in a high humidity area but I’ve just gotten use to it and since it seldom gets bad enough to block my view of the rear view mirror, I only redid the passenger’s window once around 2 years after the last edit).

Here’s the passengers seat window after treatment and reinstall, compare this picture with the first one in this section:

One thing I’ve heard about these windows is that there were some people on the forum I frequent who had noticeable water streaks between the panes or a white powdery residue disfiguring the glass. I’m not seeing much of that with my windows. Now that I’ve gotten rid of the moisture between the panes, the glass is pretty clear with just minor numbers of ‘water spots’ that are not all that visible and probably wouldn’t be noticed unless you were really looking closely.

I was happy at how well the windows were made. Sure they had developed leaks between the panes, but they are 13 years old and bounced around all the time on the road too. The holes cut into the wall by Fleetwood was also well done and well finished with two types of sealing. If the seal is good between the window frame and the side wall, there should not be much air infiltration into my rig.

Finally, I’ve heard from several people that either have, or want to try this method and most of them seem to be under the impression that the windows need to have a perfect seal. Although you may disagree, I don’t believe that’s true. For a dual paned window to fulfill it’s primary objective, all that’s necessary is a GOOD seal, not a perfect one. You want a dead air space between the panes, no air movement. But it does not have to be perfect for the window to do a good job. That’s why I didn’t try to seal the holes I’d drilled with anything other than duct tape. Sure, the tape ages and dries out so I might need to replace it some day (I’m thinking in five years), but that is a minor project. And I think the next time I do it, I’ll use sticky backed aluminum tape as suggested by a reader. Sounds like it’ll do a good job and last forever, or until I sell the rig anyway.

If you try this method, let me know how it works out for you. Thanks. Just leave a comment at the bottom of this page.