Sealing around vents on fiberglass roof (Bigfoot) - Fiberglass RV

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Old 05-12-2017, 08:58 AM   #1
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Name: GG
Trailer: Shopping: Bigfoot, Escape, Oliver
Posts: 20
Sealing around vents on fiberglass roof (Bigfoot)

About to reseal around fixtures of a fiberglass roof 2015 Bigfoot.

A common theme is "do not use silicone" (too difficult to remove, leaves residue that often inhibits use of other sealants in future).

Hopefully Bigfoot at factory does not use silicone on roof fixtures....I've asked, no reply as yet.

Have heard good things about Dicor Self-Leveling Lap Sealant (white) in a tube.

Have also heard a sealant referred to as "C2" also works well but don't see enough discussion on it for my purpose to feel good trying it.

My intent is to remove as much old sealant as possible around the fixture, clean what remains with a fiberglass friendly solvent (acetone or isopropyl), then apply the new sealant.

1. I'm VERY open to suggestions. If you've used Dicor Self-Leveling Lap Sealant in the past please let me know your results (good or bad).

2. If you have experience with other products proven successful I'd welcome those too.

3. If you've used other cleaning solvents with good success I'd like to hear about that too.

Thanks. This forum has been a savior for a 'new to RVing' type like me.


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Old 05-12-2017, 09:05 AM   #2
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Name: Greg
Trailer: 2008 Casita 17 SD
Posts: 1,534
A couple of sealants I like and often use:

Sika-Flex 231
3M 4200

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Old 05-12-2017, 12:24 PM   #3
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Name: Patti
Trailer: 1984 UHaul CT13
Posts: 451
The guy that replaced my vent easily removed the old gunk with a plastic putty knife and some denatured alcohol to clean it up. He used my butyl tape under it and replaced the screws. He used the self leveling stuff to seal. I'm about ready for a trip and plan to put additional butyl rubber caulk around it heavily like icing on the edge of a cake. Ace sells the butyl rubber caulk.
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Old 05-13-2017, 09:42 AM   #4
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Name: Kathleen (Kai: ai as in wait)
Trailer: Amerigo FG-16 1973 "Peanut"
Greater Seattle Metropolitan Area, Washington
Posts: 2,567
Second the motion on butyl rubber caulk for where caulk is appropriate. We really like it, and we did get some at Ace.

Kai & Paul
Semper ubi sub ubi.
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Old 05-13-2017, 11:39 AM   #5
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Name: Mario
Trailer: Escape
Posts: 6
3M Marine Grade Silicone Sealant

  • Adheres to bare and painted metal, fiberglass, glass, non-oily woods and many plastics and abraded rubbers
3M Marine Grade Silicone Sealant is a high quality silicone designed for the harsh marine environment. It forms a mildew-resistant, non-yellowing seal that remains flexible even after years of exposure.
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Old 05-13-2017, 02:42 PM   #6
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Trailer: 2003 Bigfoot 17 (15B17CB), 2017 Escape 17B
Posts: 341
I've seen these recommend for roof penetrations on Bigfoots: Dicor self leveling caulk with Proflex painted over that (clear,liquid formulation). I plan on trying to get the Plas-T-Cote off our BF roof and try that combination. I got this information off the Bigfoot Owners Club International site.
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Old 05-15-2017, 07:49 AM   #7
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Name: Zach
Trailer: 91 Bigfoot 17
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I used Dicor on my roof when I put in a new vent/fan and new caps on the holding tank vents. Worked great for me. Sounds like you have a few good options though.
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Old 05-26-2017, 12:32 PM   #8
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Name: Val
Trailer: 1988 Bigfoot Deluxe B19 19 ft / 2007 Nissan Frontier V6 NISMO 4x4
Posts: 454
Avoid 3M Marine in Hot Dry Climate & other POV

I just have to put in my two cents because I went with the 3M Marine Grade caulk 6 years ago upon reading about it here and it is NOT a good choice for dry hot climates like Arizona - within a few years, it turned into chalk dust in some spots and an oily, goey mess in other spots - I am having to clean it off now and it's awful. My understanding is that it works fine in humid climates but not dry.

I tried the Dicor lap sealant in one spot on my roof and will never use that again either - horribly sticky, did not dry nicely and it is hell to try to remove - much worse, IMHO, than silicone.

I tried Sikaflex but it was really fumey (chemical smell of VoCs) and I found it very hard to work with - sticky and not forgiving at all.

I do have a lot of experience caulking various surfaces from years of home improvements, but the above sealants were just not workable for me.

I used butyl tape and GE Silicone II. I know everyone says do not use silicone on fiberglass, but when I called Bigfoot Travel Trailers to ask what they used that had lasted so long around the original windows - it was silicone. I find it easy to work with and easier to remove than the above two options. Again, I am in Arizona, so results seem to vary by climate.
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Old 06-06-2017, 05:44 PM   #9
Name: Bob
Trailer: Bigfoot
Posts: 63
I just got done with this very thing on my Bigfoot TC, I had to pull the whole fantastic vent and reseal
Here were my steps:
Scrape, pull, cut and then clean old sealant off

Fill with marine fiberglass epoxy the holes left on behind that were not filled when the old AC was removed by the PO

Let that cure

Cleaned the cover, cover hing and fan mounting flange and apply butyl tape to the underside.
(side note, I got tape that was old and too narrow, so if you go this route measure the flange and get fresh tape)

I replaced the flange screws with stainless marine grade
First a dap of Dicor self leveling Lap compound in the screw holes, tightened the screws until they just got snug, I didn't want to crack the flange or pull the screw
Cut off the tape squeeze out

I then masked off 1.75 from the vent flange on the roof of the RV with 3M blue tape
Then used the Dicor, I ran the edge of the flange, over each screw hole and around the hinge of the vent cover.
I let that kick and went back over looking for areas where the dicor may have sunk or flow away from the flange.

With the tube I also re-coated a couple of other roof penetrations, first cleaning the old sealant with alcohol and a stiff nylon brush. I also was able to pull up old silicone caulk that was use to seal before.

Dicor is messy even more than silicone and it runs quick, so cut your tube's nozzle small, it will take a little longer but it would be easy to control. I suggest using some on a practice sheet first to get use the speed, and keep rags handy, and use a caulking gun that backs off the pressure on the tube as soon as you remove pressure from the trigger otherwise you will have flow.

When I do the next vent I might try Eternbond tape if I find some more positive reviews about it.
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Old 06-14-2017, 09:02 PM   #10
Name: Derek
Trailer: 2007 Bigfoot 25b25rq
Posts: 69
I just scrubbed the old surface clean and then put another coat of Plastic-T-Cote over the top. This is the second time I have refreshed the coating.

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Old 06-15-2017, 04:08 AM   #11
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Name: Gerry
Trailer: 1979 Boler 1300 / 1991 Casita Freedom Deluxe
Posts: 1,688
On my larger camper, a Holiday Ramber with a fiberglass roof, I have a problem with water pooling up around one of my vents, and upon opening up this spring had wet ceiling. Thank good it is styrofome for insulation and it will dry and not stay soggy like most fiberglass insulation. Anyway, after drying area and getting as much gunk/tape/and more gunk off outside of vent and wiping down area with alcohol, I slathered on Dicore roof patch all over this area. This product goes on like mashmellow with a putty knife and self levels and seeps into little holes and cracks....Been 2 months now with the rainiest May we ever had in Maine and even though there is 1/2 of standing water around vent none gets inside.
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Old 03-27-2020, 11:19 PM   #12
Name: Bob
Trailer: Bigfoot
Posts: 63
So digging up this old thread as I had to replace my fridge vent.
And I had to remove layers and years of dicor, plast t cote, silicone and other materials.

The OEM seal PlasTCote hardened to hard plastic on my 2000, the repairs I did back in 2017 were still soft enough to easily dig out. The silicone still a mess. There was something else used that cured to a very hard surface.
I wasn't able to get it all off but cleaned it up as best I could.
Thankfully the sealing surface is clear.

I went again with Butyl tape and Dicor since I have some on hand and now in the middle of Covid 19 I am not going to the store to get something else or have something else shipped. And the plasTcote was so hard to get off. I would rather make the fix easier in the future.

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