IS OSI the only caulk you can use on fiberglass? - Fiberglass RV

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Old 07-04-2016, 09:18 PM   #1
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Name: Margaret
Trailer: in the market
North Carolina
Posts: 197
IS OSI the only caulk you can use on fiberglass?

I talked to the Parkliner manager, and he was very amenable to customizing the Parkliner except for the caulk; he said OSI is the only caulk you can use on Fiberglass. Oh, and he also said he had to use a spray adhesive.

So . . . if you've been following my posts, you know that I'm chemically sensitive. I have seen excellent reviews of OSI for durability, but its specs seem to indicate that it's pretty toxic, and that it can cause health problems while still wet, at least.

Is OSI really the only caulk you can use? Can caulk be sealed with a special sealant like AFM that would prevent off gassing?

What I've noticed about campers in general is that when you're in the hot sun, the chemical smells tend to come out more (most campers that are for sale are parked out in the sun, and of course it's summer, so . . . .).

Anyway, do you need the OSI caulk to prevent leaks?


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Old 07-05-2016, 10:10 AM   #2
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Name: Walter
Trailer: 2002 BigFoot 17'
SW Virginia
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A lot of folks are recommending butyl tape instead of caulk these days. That's what Little House Customs uses.


Past owner of 1995 13' Casita, 1994 16' Casita, 2012 Parkliner.
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Old 07-05-2016, 11:00 AM   #3
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Sounds like Parkliner is not willing to use any other product. I suggest you shop different manufacturers.
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Old 07-05-2016, 11:05 AM   #4
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Name: Steven
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There are lots of other caulks besides OSI but many use the same or similar ingredients. One of the issues with the older / cheaper caulks was that they dried out and became brittle , had poor adhesion to many substrates ,and most required painting to provide UV protection. Modern caulks hold up better ,stretch , are easier to tool , have better adhesion and stay flexible over long time periods , They are chosen because they work well and are relatively inexpensive. I doubt off gassing is even a consideration for most trailer manufacturers / builders. You may well find a caulk / sealant that solves your toxin issues but it may lead to other issues such as a leaking trailer or the caulk requiring constant maintenance.
I would assume that Parkliner uses OSI because it has a proven track record in their application and not lead to leaks / warranty issues.
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Old 07-05-2016, 11:44 AM   #5
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Name: Donna D
Trailer: Escape 5.0 TA, 2014
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Interesting. I've never even heard of OSI caulk and I've owned an all-molded-towable longer than Parkliner has been in business.
Donna D.
Ten Forward - 2014 Escape 5.0 TA
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Old 07-05-2016, 11:56 AM   #6
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Name: Jon
Trailer: 2011 Escape 17B
Oswego, NY
Posts: 1,275
I've been happy with butyl caulk, Dicor Self Leveling Caulk for horizontal surfaces like vents and other things on the roof, and Geocel ProFlex for everything else. ProFlex comes in clear & white, stays flexible, is paintable, sticks to itself (unlike silicone) and makes great glue.

What ever you use, avoid anything silicone based. It doesn't always stick to fiberglass, will not stick to itself, and leaves a film that is almost impossible to remove when you need to recaulk.

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