Plumbing vent cap sealant type? - Fiberglass RV



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Old 03-22-2019, 09:36 AM   #1
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Plumbing vent cap sealant type?

One of my Casita plumbing vent caps has deteriorated and needs to be replaced. The instructions for the new cap says to use silicone sealant around the rivets under the vent cap, then to seal the cap perimeter and also the tops of the rivets. I do have all of the old silicone sealant removed and have thoroughly cleaned the old sealant off with mineral spirits. No old silicone is there that I can see nor feel. Can OSI Quad be used in lieu of silicone? Or perhaps a smooth urethane sealant? From what I have read silicone is a no-no on fiberglass but want to do it right the first time.


thanks for your suggestions.
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Old 03-22-2019, 10:28 AM   #2
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I would use a polyurethane adhesive/sealant such as 3M 5200. Alternatively I have also just used a copious quantity of butyl tape.
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Old 03-22-2019, 02:31 PM   #3
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My opinion is that 3M 5200 is bad advice unless you are positive you will never, ever need to remove that connection. 5200 is an adhesive for permanent installations. I think you will be very pleased with Dyco 20/20. It is available in quarts to brush on and in tubes for caulking guns. It is one of the best products I have found. Tough but stays flexible. I like the brushable version in quarts. If you keep the lid tight it will stay workable for some time. With 5200, once you cut the tip off the whole tube will harden within a few days. Don't get me wrong 5200 is an amazing product but it can be your enemy.


https://dycopaints.com/products/dyco-20-20-seam-seal
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Old 03-23-2019, 06:10 AM   #4
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Quote:
"One of my Casita plumbing vent caps has deteriorated and needs to be replaced. The instructions for the new cap says to use silicone sealant around the rivets under the vent cap, then to seal the cap perimeter and also the tops of the rivets. I do have all of the old silicone sealant removed and have thoroughly cleaned the old sealant off with mineral spirits. No old silicone is there that I can see nor feel. Can OSI Quad be used in lieu of silicone? Or perhaps a smooth urethane sealant? From what I have read silicone is a no-no on fiberglass but want to do it right the first time."
i've a couple of suggestions...

since you're going up on the roof why not replace both vent caps? if one has gone bad, the other can't be far behind.

if you paint those caps before installing with krylon (white) paint they will last much longer as that paint has a uv protectant.

as far as what you seal it with...silicone will work fine as will the alternatives. the point is to get as good seal whatever you use.

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Old 03-23-2019, 06:39 AM   #5
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Good suggestion about painting with Krylon. I have some leftover from another project. Think I'll do that.
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Old 04-10-2019, 01:32 PM   #6
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I find Dicor products work well
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Old 04-10-2019, 02:06 PM   #7
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It's pretty hard to get silicone completely removed and if any is there it will make a good release agent. I don't think mineral spirits will cut it very well. In this case, it was not the silicone that failed and Casita recommends using silicone. Plus, you were able to get it apart to replace it.

I'd say do it with silicone, as Casita did and recommends. Easy to get, cheap, available in small tubes to reduce waste, can be re-done later if needed. You can also get paintable silicone which acts exactly like regular silicone, but can be painted. Good stuff.

The main place you might want to avoid using silicone is on an area that might get a glass repair or paint later, but you already have silicone on this spot, so no problem.
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