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Old 10-22-2017, 01:47 AM   #1
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How do you seal fiberglass body panels?

I have a few fiberglass seams in our 1991 Collins short bus that are leaking slightly when it rains.

I have thought of plugging the seam from the outside with something like epoxy, but am curious if others have done so or done something similar.
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Old 10-22-2017, 01:56 AM   #2
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Quote:
Originally Posted by Puggy View Post
I have a few fiberglass seams in our 1991 Collins short bus that are leaking slightly when it rains.

I have thought of plugging the seam from the outside with something like epoxy, but am curious if others have done so or done something similar.
There is no such thing as a slight leak.

Read this post for ideas.
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Old 10-22-2017, 02:29 AM   #3
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Pretty vague thread, beyond talking about "Through The Roof" stuff - which is pretty vague in its description, at least at Through the Roof! by Sashco - Roofing Sealant & Caulk Is there something in there I'm missing? It's got that "Marvel Mystery Oil" style to it, light on what it is, heavy on promise.

Epoxy sounds a lot better. I know I can paint it, I know I can put it on a vertical seam if I use fast drying stuff, and I know it's going to seal a tight/small steam where two pieces of fiberglass join together. The fiberglass isn't cracked, it's just old seams that are a bit weepy at the joint.

I also have used Eternabond type tape on a few metal seams from the roof lift, and it does seem to work well. Perhaps it will work on these seams.
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Old 10-22-2017, 10:34 PM   #4
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Well.. what would you like to know and I'll try to un-vague it for you.

Through the roof is a synthetic liquid rubber. It sticks like tar (to everything) but according to the manufacturer.. wont shrink, crack, etc.. and has a lifetime warranty. I talked to a few locals who used it to seal up roof seams on horse trailers, etc.. before using it on the bus.

So far.. this stuff has worked great. It bonds extremely well (tried to remove some of it from an area around a window... not happening unless you use a wire wheel on a grinder or lots of patience with a razor blade). It solved my issues but its not all I'm using. I'm reinstalling the gutters and moldings using the proper butyl tape (which should seal out water on it's own). It can be applied vertically as long as it isn't applied too heavy.

Keep in mind what ever you end up using needs to have some give or it will end up cracking/leaking again as the bus moves. These bodies flex and give quite a bit so a seam glued together with something that sets up firm will either crack back open in short order... or cause another area of the fiberglass to crack. They are assembled in panels to allow for movement without causing damage... so a bit of flexibility is required. DONT use silicone or anything of the like... it wont stick and will fail.

Are the seams in an area that use a molding to cover them or are they lapped exterior skin seams? Have any pictures of the problem areas?
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Old 10-27-2017, 07:59 PM   #5
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The leak is in this vertical seam circled in red...



The panel on the left is fiberglass, and metal on the right. They fit together a bit like this if you took a horizontal cross section...

_______||_______/

There is some kind of old sealant between the two butted pieces (the || part), and screws holding them together.

There's very little (to no) gap between them really. Water is ever so slightly seeping into the gap into the inside. You don't see drips, but it feels "moist" basically.
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Old 10-27-2017, 08:04 PM   #6
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I would use some form of automotive seam sealer or a product similar to "through the roof" that is designed to adhere to fiberglass yet remain flexible.

I like the through the roof stuff but I'm sure there are other products like it out there. I used it on several fiberglass to aluminum seams and fiberglass to fiberglass. It would require a grinder or sharp knife and lots of time to remove. Stays very flexible and is cheaper then "RV Sealant" which is nothing more then silicone that wont stick for long.
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Old 10-27-2017, 08:09 PM   #7
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Thanks, I appreciate the input on the material and will look further into it.
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