Caulk - Fiberglass RV

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Old 07-17-2009, 01:53 PM   #1
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Trailer: Bigfoot 21 ft Rear Bed
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Sorry in advance if this topic has been beat to death but I just finished installing two FanTastic fans on my Bigfoot 21RB and I'm less than satisfied with the Dyco C-10 caulk used. The caulk went on well enough and looked good immediately after its application but yellowed after less than a month. I chose this product based on positive feedback and shied away from silicone because of the negatives I've read. I expressed my displeasure with Dyco and they in turn recommended silicone for color retention and flexibility. So, what do you folks use for sealing roof penetrations? What disadvantages are there in using silicone?

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Old 07-18-2009, 09:24 AM   #2
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Name: marvonw
Trailer: 1978 Trillium 13 ft
Great Lakes area-US
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I just finished installing two FanTastic fans on my Bigfoot 21RB and I'm less than satisfied with the Dyco C-10 caulk used. So, what do you folks use for sealing roof penetrations? What disadvantages are there in using silicone?
...My FanTastic fan was installed by the head technician at the FanTastic vent factory. He used "Dicor Lap Sealant, 501 LSW". This was just last month, so I don't know about discoloring, but the installer claims it is the only thing to use for installation.


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Old 07-18-2009, 05:31 PM   #3
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Trailer: 84 16 ft Scamp
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After I installed a MaxFan on our Scamp using the tan colored tape the seller recommended, I noticed a slight sag in the roof at the forward side of the fan. Sure enough, I got a small leak -- not much, but after a heavy rainstorm there might be a tablespoon or two on the floor underneath the fan.

I removed it an bedded it in with 3M 5200 available at the local Home Depot as well a Boating shops. This was the end of leaks. I'm not nearly tall enough to see over the top of the Scamp so the color of the caulk is of little interest to me, but the ability to keep water out is!

One caveat -- items mounted with 3M 5200 are all but impossible to every remove in one piece!
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Old 07-19-2009, 12:54 AM   #4
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As you can see its compatible with fiberglass.

I too read much about the disastrous results with silicones and fiberglass together...


At the risk of wrathful indignation from the butyl purest who beat the drums of anti silicone warnings I flatly say I have had no problems with silicones as long as I choose the correct silicone chemistry for the correct applications....Silicones come in many complex chemistries so there is reason for confusion...The sealant may not make a good adhesive for instance, yet a silicone rated as both may be great but not on some materials over others when that material is not specified in the label recommendations.

Silicones clean up well between uses, they take a high heat well where butyl craps out at about 180 F, the flex in the right product is unparalleled.

The new urethanes for marine applications do work well but are tacky enough to be a problem for myself.

Most shops fall victim to the recommendations of "sales" representatives of wholesalers who peddle this or that...When visited I ask for the specification sheets and test data sheets and the M.S.D. sheets before I consider it as a part of my operations.

I would argue that fiberglass trailers should NOT be treated as R.V.s in the classic sense of the traditional use of sealants and bonds, rather I argue they are more like boats, think land boats if you must...The technology employed needs to come from that sector in regards to bonds and sealants is my belief.

I do want to blow up the myth that silicones are evil where fiberglass is concerned...

In 99% of the cases concerning material incompatibilities the information about the product was either not understood or ignored...Silicones like plastics are a broad category of chemistries, like different plastics silicones need understanding before application begins in any job.

Happy Camping, Safe trails.

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Old 07-19-2009, 04:33 AM   #5
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Name: Steve
Trailer: 2003 Casita 16' SD
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I have a sailboat and have used marine silicones without issue for 20 years. I use marine silicones (and marine hardware) on the Casita.
Quando omni flunkus, moritati
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