Waterproof sealant for PVC

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Waterproof sealant for PVC

Postby KelseyL » Sun Jul 25, 2021 11:35 am

Hello,
I’m doing some work on our teardrop we bought last fall. We’re pretty sure the exterior is painted PVC paneling. I’m installing a fantastic fan and need a waterproof sealant. What is the best type of sealant for painted PVC? I keep hearing that you shouldn’t use silicone on RVs, so I’m not sure what’s best.

Thanks for the help!
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Re: Waterproof sealant for PVC

Postby Minics04 » Mon Jul 26, 2021 5:49 am

I use ProFlex RV Sealant with good results, but you might get lots of different options from everyone. Just my 2 cents!
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Re: Waterproof sealant for PVC

Postby Socal Tom » Mon Jul 26, 2021 8:53 am

RVs generally use a putty to seal around windows and roof vents. Here is a good article I stumbled across https://www.rvtravel.com/seal-out-the-w ... utty-tape/.
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Re: Waterproof sealant for PVC

Postby tony.latham » Mon Jul 26, 2021 9:07 am

I’m installing a fantastic fan...


I have never had a problem (or a leak) using butyl tape for sealing a vent fan. I would suggest caution using a sealant that can easily turn into an adhesive since a fan is a mechanical device that can fail.

I run a bead of clear OSI sealant around the installed fan housing as insurance. If I build another or replace my fan, I'll probably switch over to Proflex for this ––I haven't used it but hear great reports.

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:thinking:

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Re: Waterproof sealant for PVC

Postby Tomterrific » Tue Jul 27, 2021 8:34 am

I used a product from a home center store called rope caulk. It is similar to the putty tape talked about in the article linked by Tom. It has sealed everything I have installed on my camper. A trick I used to seal the small screws is to use finish washers and fill the hollow with the putty. When the screw is tightened the putty squeezes out and seals completely. The finish washers look great and the putty caulk makes a good seal. I used the same method on the window flange.
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Re: Waterproof sealant for PVC

Postby KelseyL » Wed Jul 28, 2021 3:55 pm

Thank you for all the advice!

I did use butyl tape as the main sealant for the fan, but the instructions on the fan say to add a waterproof sealant around the edges and over the screws.

I took a piece of the trailer exterior into an RV shop and asked what they would recommend. Turns out it’s not PVC, it’s filon. Reading up on filon that makes sense and describes it perfectly. It’s a very thin layer of plastic/fibreglass stuff on a thin layer of laminate wood. The RV guys recommended the same ProFlex RV sealant that you guys did so thank you!

I do have a new problem though. When I was on the roof I saw that a repair made my the previous owners failed and there’s a big crack in the filon on the roof. It had been caulked with something but whatever the sealant was cracked along that fault line. It started at where the old vent corner was.

Image Image


I scraped off all the old sealant and now need to re-patch this. I did look under the crack as much as possible and it doesn’t look like there’s any water damage under the filon. It’s extremely thin and below it is an inch of styrofoam so there’s really nothing to rot. We also, thankfully, live in a desert so it’s been hot and dry all summer with very little rain so any moisture would have been well dried out.

Image Image

Can I just use the ProFlex RV stuff to seal the edges of the crack back together? A different forum was talking about chiseling away the rough edges and fiberglassing in the crack but that seems fairly challenging and we’d never get it to match. Sealing it with clear sealant won’t be completely un-noticeable, but it would at least blend enough since it’s on the roof. A huge stripe of fiberglass would be much more obvious.

Any advice you could share would be so helpful! Thanks for all the help so far!
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Re: Waterproof sealant for PVC

Postby Socal Tom » Wed Jul 28, 2021 5:19 pm

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Re: Waterproof sealant for PVC

Postby tony.latham » Wed Jul 28, 2021 8:53 pm

A huge stripe of fiberglass would be much more obvious.


Sealant won't fix the break. I would figure out a way to pull it together and then fix it using a 4-6" piece of fiberglass cloth (6 oz perhaps) and epoxy. It's not a big learning curve.

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You'll have to remove all of the sealant, of course.

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Re: Waterproof sealant for PVC

Postby KelseyL » Fri Jul 30, 2021 9:52 am

Thanks Socal Tom. That’s the forum I had seen before and was hoping to hear that fibreglass wasn’t necessary, but it sounds like it is.

I appreciate the advice Tony. I did look up the process and it doesn’t seem that intimidating when it’s broken down. They have a Bondo kit at Canadian Tire. Online I read that Bondo isn’t the greatest quality in the world but should work just fine for this application. Do you have any advice or recommendations for what product to use?
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Re: Waterproof sealant for PVC

Postby tony.latham » Fri Jul 30, 2021 12:50 pm

They have a Bondo kit at Canadian Tire.


I'm not familiar with that stuff. I recommend you use epoxy resin, not polyester like I assume the Bondo stuff is. Epoxy has a much higher adhesion. You'll have to remove the gunk the previous owner used and sand the filon down through the color.

And of course, you'll need to paint the patch. :frightened:

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