Silicone on Fiberglass - Fiberglass RV


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Old 05-27-2020, 07:56 PM   #1
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Silicone on Fiberglass

Before I ever even saw my first fiberglass RV I found this forum and started reading. I quickly found out here that silicone on fiberglass is a No No. This was news to me but I will always defer to people who have had experience.

Well imagine my surprise when I found out that all of the sealing on my BigFoot is done with silicone. While I was removing my graphics I had to R&R the outside AC outlet cover. Well that was glued on so tight I had to cut it off with a razor knife. Now I know what everyone means about the silicone. It took me quite a while to get it all off.

I resealed it with some grey butyl putty on a roll that I had leftover from working on my old camper.
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Old 05-27-2020, 09:14 PM   #2
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As I understand it, the problem with silicone is that it won't stick to itself. So, you have to remove all traces of silicone before applying new silicone.

Of course, Home Depot does sell silicone remover.
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Old 05-28-2020, 12:37 AM   #3
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Just a note for information about silicone caulk from a company that makes caulking, Shasco. This article explains in everyday language the issue of using silicone caulking. I am not using their caulking on my trailer, just linking to this article because it is easy to read and understand without it's being overly technical. They do have a brand of silicone remover they recommend.

https://blog.sashco.com/blog/0617201...stick-silicone


On my trailer where a previous owner had used silicone caulk I used Mostenbocker Silicone Caulk remover which I purchased at my local hardware store. It took a few applications to get every spec of the silicone caulk off the surface. I wanted to paint my trailer so I needed to be sure all the silicone was completely gone. The proof it worked great was in the fact that after a year and a half my paint job has shown no signs of peeling off in that area. Also no orange peel effect in the paint in that area.
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Old 05-30-2020, 12:49 AM   #4
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On our YM 2000 Bigfoot 1500 camper, (A slide-in truck camper)
Bigfoot used clear silicone sealant, on the side sealed openings, holes, doors, flaps, plugs and vents as well as around the clearance lights and around the bond-line top and bottom.
The windows were sealed with something else, maybe black buytl tape.


On the roof the the center vent fan was sealed with a foam gasket and dicor (but that was added after the AC unit was removed) the rest of the roof penetrations were done with what looks like Heng's Plas-T-Cote and they were masked off and rolled or brushed on over the seam and the screw holes so it left a very crisp box around the square openings.

When I replaced the fridge vent, (Damaged by way of the low hanging fruit)
I cleaned up the old Plas-T-Cote, then layed down buytl tape then the vent then some Dicor self leveling Lap compound, after I had masked off so it wouldn't be too messy,

When it comes time to fix some of the side penetrations I suspect I will use the same processes I outlined above, but switch out the self-leveling for silicone sealant or no sag vertical surface Dicor.
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Old 05-31-2020, 05:46 PM   #5
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Timely thread for me. I'm finally almost done with moving my Battle Born Batteries inside my Bigfoot. There was an existing hole in the floor where the ground wires pass through from the converter, plus some other wires. I pulled the silicon out of the top and bottom of the hole and passed my 3 new wires from the batteries (2 6 AWG wires for the solar panel, and the 4 AWG ground wire). I've removed as much of the silicon as I can see, and scraped the underside with a razor.



I had planned to just fill in from the top and bottom with new silicon. Should I be using butyl tape instead?



Pictures from the top and bottom of the holes to be filled.


Thanks in advance!
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Old 05-31-2020, 06:50 PM   #6
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I have found that wherever a "gasket" kind of seal is required, like between the window frames, vent frames, and your trailer fiberglass, 1 inch wide butyl strips are the best way to go. Easy to apply, flexible, easy to control.

Butyl also comes in tubes but be warned that goop is very difficult to control, and it is extremely hard to clean away mistakes. Silicone does provide a very aggressive adhesion but I believe over time it tends to produce tiny pinholes that will encourage leaks. And dirt sticks to it.
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Old 05-31-2020, 07:39 PM   #7
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Jon, for your application (sealing around wires inside a grommet hole), butyl tape is not necessary because there is no contact with the molded fiberglass shell. Also the butyl might actually seep out of the grommet hole. In this situation, either silicone caulk or another type of drying caulk might work better. I actually use DAP Dynaflex 230 to seal around wires and propane tubing inside grommets.
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Old 05-31-2020, 07:54 PM   #8
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WD40 will lift the silicone caulking fast.
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Old 06-01-2020, 06:43 AM   #9
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Quote:
Originally Posted by Daniel A. View Post
WD40 will lift the silicone caulking fast.
Agree. A previous owner had replaced all of the 50 or so rivets on my Boler 17 fiberglass shell with carriage bolts. He/she had encased each bolt head in silicone caulk resulting in a silicone caulk blob over and around each bolt head about 1.5 inch in diameter.

The bolts still rusted out and some leaked. I was able to remove all of the silicone blobs using plastic razor blades and wd40. And no damage to the gel coat.
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Old 06-01-2020, 08:57 AM   #10
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PorFlex is a close equivalent for silicone & has the advantage that it can be applied over itself, paintable, etc. A bit more expensive than silicone, but a better choice for RVs.

If you are looking for a sealant designed for roof applications, Dicor self leveling lap sealant works well.
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Old 06-02-2020, 03:29 PM   #11
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Thanks for the answers all. The Porflex looked good but it says not to use where there is polystyrene insulation sheathing, which I think the Bigfoot has.



I think I'll clean up as well as possible and see how the silicon works. It's only going to get splashed while driving, and it's an easy enough area to inspect and replace if needed. I will clean the area with WD-40 first though.
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Old 06-06-2020, 12:28 PM   #12
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Silicone on Fiberglass

When I bought my then 19 year old Casita there were some cracks on the top side of the belt line and the shop that repaired the axle tld me to cover them with silicone caulk to keep water out of the lamination. I had fiberglass boats in the past and I know I should keep water out of any area that could de-laminate. No one in the boating world ever suggested silicone for that purpose so I used the gray JB Weld product which filled the area and sealed the cracks. I do monitor for more but there were only 3 places that needed attention, not bad for 19 years (now 21) and a trip to Alaska by the prior owner.
Those who noted we should not use silicone sealant over old are 100% correct, I learned about this on a sailboat window repair...thankfully I did it right.
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Old 06-06-2020, 10:17 PM   #13
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I wish I had read this thread two days ago! Just finished removing the awning case from a 16 ft Casita. There were 20 rivets holding the case to the shell plus a 1" thick rope of silicon gluing it in place. After removing the rivets, the case was stuck fast to the shell. I had to use a garden shovel to pry the case away and free it from the silicon. The rope of silicon was still stuck to the shell, so I used a scraper with a razor blade to cut away most of the silicon. There was still a thin layer of silicon so I ended up using a sander to sand it away. If I had known about WD40 it would have saved at least a day of labor!

By the way, if anyone wants a free awning for a 13ft or a awning case for a 16ft, they can have them if they can pick them!
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Old 06-07-2020, 11:10 AM   #14
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Originally Posted by Daniel A. View Post
WD40 will lift the silicone caulking fast.
As will any petroleum based liquid as silicone is not compatible. You still have to the silicone remover treatment to clean off the fiberglass.
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Old 06-07-2020, 05:27 PM   #15
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silly repairs with silicone :umb

I spent most of today removing silicone that was not working. Silicone will not stick reliably to fiberglass with gelcoat as wax is used to harden it. Lexel works and will stick to wet items even but is very hard to work with.
The rivets holding the awning track leaked and the filled the entire area with silicone a two inch wide swath beyond the track what a mess and it still leaked !!!!!!

hard to get off trailer and the parts, how can it stick in patches?

Stanley closed end rivets in the old and new tracks at every fix no more leaks.

silicone cost us a set of light lenses when the bulbs went as they were silconed on

Removing and replacing all body rivets the caulking was not working anyway so fixing it the best way with new Stanley closed end marine rivets

We have had our trailer for years and are still removing leaking silicone!!!!
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Old 06-07-2020, 05:30 PM   #16
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silly silicone our trailer bane

Quote:
Originally Posted by ThomasC View Post
Before I ever even saw my first fiberglass RV I found this forum and started reading. I quickly found out here that silicone on fiberglass is a No No. This was news to me but I will always defer to people who have had experience.

Well imagine my surprise when I found out that all of the sealing on my BigFoot is done with silicone. While I was removing my graphics I had to R&R the outside AC outlet cover. Well that was glued on so tight I had to cut it off with a razor knife. Now I know what everyone means about the silicone. It took me quite a while to get it all off.

I resealed it with some grey butyl putty on a roll that I had leftover from working on my old camper.
Feel for you "silicone will not stick to silicone" and it hates gelcoat.
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