Silicone vs Butyl for water leaks - Fiberglass RV
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Old 04-16-2021, 11:46 AM   #1
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Name: Alex
Trailer: Scamp
Montana
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Silicone vs Butyl for water leaks

Hi all! Iíve seen so many different opinions on here and other sites about sealing up fiberglass RVs. Iíve got a 1993 Scamp 16í that has a few window gasket leaks. The front (plexiglass) window gasket is old/cracked enough that Iíve just ordered the replacement gasket from Scamp.

Two of the side windows (rear by bed/dinette) have gaskets that are pulling away a little bit at the top and Iím noting some previous water damage on cushions. Iíd like to fill those gaps for now and Iíve read a lot about staying away from silicone sealants.

I picked up this product at my hardware store and my question is, is this a good product to use to seal the gaps in those window gaskets?
Iím also looking for something to seal where the bolts pass through the fiberglass for brackets that previous owners mounted (for TV antenna I believe). I hope this same product can work.

Any info/suggestions much appreciated!! Thank you
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Old 04-16-2021, 11:59 AM   #2
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Trailer: 1978 Trillium 4500, 1979 Boler 1700
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Most commonly used and best sealants to use on travel trailers are butyl tape and various marine type sealants such as 3M 4200 and 3M 5200. Butyl tape is commonly used to re-bed the window flange when re-installing, but also for roof vents, and any other through hull components. 3M 5200 or 4200 work better on small fittings and through hull screws and bolts.

Silicone sealants are problematic on molded fiberglass trailers because they are extremely difficult to remove when doing a refit (ask me how I know this), and they are not compatible when doing subsequent re-sealing even with old silicone sealant.

EDIT: I bought a "vintage" molded fiberglass trailer with large amounts of silicone sealant around the windows and roof vents, and they ALL leaked!! I had to remove all of the silicone sealant completely and remove and re-install all of the windows and roof vents. I filled a two gallon bucket with old silicone sealant from the roof vents.
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Old 04-16-2021, 12:07 PM   #3
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I have found that butyl tape is not as reliable for sealing small fittings such as single screws and bolts, probably because of the very small surface area being sealed together with the fact that small fittings tend to move/vibrate more while towing. I have however had good luck with sealing snap caps with butyl tape.
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Old 04-17-2021, 09:41 AM   #4
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Name: Michael
Trailer: Trail Cruiser
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I have used both and found butyl tape to be better. Silicone is OK to seal small opening but if I have a leaking window I remove it, check for and repair any internal damage and reinstall with butyl tape. And yes, removing old silicone can be a challenge.
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Old 04-17-2021, 10:28 PM   #5
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Trailer: 1978 Earlton boler 1700 RGW
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Would never use silicone on a fiberglass trailer. Silicone will not stick to old silicone and is hard to completely remove from fiberglass. If you do not want to remove the window they make RV caulking that is clear and works well. Silicone was used a lot on our trailer before we got it. They even siliconed the light lenses. Bulb burned-out and cracked the lens getting it off, stoke of luck got a new replacement that time and made new lens gaskets.
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Old 04-17-2021, 10:55 PM   #6
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Sikaflex! I believe its a Urethane compound, goes on a lot like silicone, but seals MUCH better. available in clear, white, and black, probably others.
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