Seams on Big Foot - Fiberglass RV

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Old 06-09-2008, 11:41 PM   #1
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Trailer: Bigfoot 25 ft
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I have just completed a clean up on the exterior of my BigFoot TT. While on the roof I noticed that the seams look like they are cracking. Even so, no water was found inside the trailer after some fierce winter rains (several inches per night). Does this need immediate attention? or is it not broke and therefore require nothing? Finally, if it needs repair, what have folks used on these seams (around vents, AC, skylights etc.)?



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Old 06-10-2008, 06:15 PM   #2
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Trailer: 1971 Astro (ie. Campster/Hunter I)
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I would do it,
Despite howls to not fix what is not broke...

I would use the flat butyl cord that you can buy at the R.V. store, its cheap, lasts years and as the coach flexes the seal flexes with it. This stuff goes from freezing to 100 plus F in a day surface temps as a normal coarse of operation, when it gets old and stiff because of age the seal becomes compromised because this stuff gets brittle. And normal thermal expansion and contraction will occur...I have tried other solutions in better chemistry not available in the day when yours was built, the results have been my learning that the sun was of far more consequence to the seal than the water ever was...The eventual leak is the result of not doing the maintenance really...Since your in Southern Cal we have something in common...The sun...I hate ruining a trip with a minor maintenance oversight to only end up hanging out sleeping bags to dry all day...Being that you live in southern Cal Bro, aren't you guys supposed to be ready to high tail it outa there in 5 min or less?

Joking aside, I would make a mental note doing it as a part of normal maintenance every 10 years...It goes along with packing the axle bearings and flushing the fresh water tanks every luv the trailer.


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Old 06-10-2008, 10:39 PM   #3
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Trailer: Bigfoot 25 ft
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Thanks Harry,
I was surprised to see the material around the roof "fixtures" cracking already as the trailer is 2005 model. I don't know what BigFoot used up there. Its nearly white, looks like it went on as a thick, gooey substances that ended up being kinda shiny. It looks now like the edges around the sky light and vents is cracking. I agree its not fun to interrupt a trip. I am heading north for the summer and most likely will need to be waterproof repeatedly. I'll take your advice and look for the flat butyl stuff (do you know the name of it?) at the RV store. Our only one here in town went out of business this spring.
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Old 06-11-2008, 11:23 AM   #4
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Dear Dennis,

The "white stuff" is giving out on a lot of trailers that I have worked on, its adhesion properties to new fiberglass can be questionable when the sealant is applied to soon after the curing process and the amine blush is not washed off (with soapy water) prior to application...A fiberglass safe solvent which leaves no residue should be used in a second wipe down on mating surfaces letting it dry before the white silicone based stuff works well.

The info I got was from a chemist I work with...he is smarter.

I know this is more than you asked for, its all about modern chemistry today and salesmen who represent huge companies and their products and costs to purchasing agents...Calling the RV manufacturers can help if they are available...But that does not always work...Parts departments will tell you what they are currently selling but not necessarily what it was built with.

I also note here that manufacturers do not exactly feel the obligation to build beyond the warranty period, some better ones feel a lifetime of an RV is 10 years...Not exactly the common owners point of least not mine...This attitude is often in the decision process when materials are purchased for their RV construction as well as RV costs.

Fiberglass cures with an amine blush that can react with the adhesion properties of silicones (acid cured) if you want to use the same stuff that's ok...but what that "stuff" was is often lost as information after a production run...more yet after a few years down the time line, the information just was not important enough to record.

It can even change year to year by the manufacturers of the adhesives themselves...
The recipe of the adhesives change as their formulas evolve according to market niche requirements.

Generally, make sure to wash the amine blush off the seal mating surfaces (shows as a powdery white) with water and mild soapy water...then dry, use a safe solvent to clean the area and re-apply any quality RV sealant.

A good test to determine composition of an exsiting sealant as a pure silicone one is a lighter test...The silicone will not burn well, the others melt and burn like wax.

GE had a recall on silicone sealants...that failure in chemistry was awful for me...I had boxes of it...It took 7 months to get the credit from them.

I still like the corded stuff...Its known at the counter as gasket cord or cord putty, region names change...describe it, they will know catalogs its known as butyl tape.

One exception to this...If the sealant was the only means to hold the vent in no scews or fastners used...then you MUST use a sealant/adhesive!!!!

The most popular manufacturers of current good RV sealants are Silaflex 221, Parr parlastic sealants are being used now...The older silicones were popular in the 90s.

I would caution fiberglass owners on water vulnerabilities because the illusion is they are plastic and "water proof", they are not "water proof"... the gel coat when intact is... that notion of "water proof property" gets compromised in any penetration of the hull gel coat, the glass fibers beneath it will wick moisture and cause swelling, blistering or cracking from within or rather behind the gel coat.

Like the hole penetration for your vents etc.

Have many years of RV fun, those are really great trailers, taken care of it and it will last longer than we will live.

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Old 06-12-2008, 02:41 PM   #5
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Trailer: 1999 Scamp 13 ft and 2003 Bigfoot 17 ft (15B17CB)
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Harry and Dennis,
I noted something similar on our new-to-us Bigfoot, when washing it up this Summer. The frig vent, fan, and bathroom vents all have cracks in the "frame" material used to seal the perforations to the trailer. The cracks are where the flange meets the trailer roof. I thought the material looked like rubber roof menbrane. No leaks and thought I would have the "frames" replaced at the RV service place next Spring, as we will have it in storage (inside) until then.
Is this the same problem? Is butyl the fix?

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