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Old 09-17-2015, 08:09 PM   #1
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1968 30' Sovereign
New Richmond , Wisconsin
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Did we use the wrong sealant on Fantastic Fan install?

This last weekend, we replaced the two noisy/barely working ceiling fans in our 1968 Sovereign with two Fantastic Fans. After reading advice on some of the threads here, we seated the Fantastic Fans using Vulkem - Trempro 635 ( we also used the "gasket" provided by Fantastic Fan.)

Once we smoothed out the caulk to make it look presentable. my wife noticed that some bubbles were popping up in the Trempro. We did the best we could to smooth those out and called it a day as night was upon us. Checking our work the next morning, we found numerous bubbles on the Trempro on both fans, some the size of a small fingernail. The bubbles have not popped - and they are still there until we figure out what to do. Interestingly, the Trempro is stuck fast to the aluminum and has created a beautiful seal around the perimeter of the fan - but it easily comes off from the top gray flange of the fan that is screwed down to the aluminum roof.

I have since been told that we should have used Trempro 644 RTV Silicone instead of the Trempro 635 because Fantastic Fan has changed the composite of the plastics used in the fan.

Has this happened to anyone else out there? Is there any way to salvage this without having to remove all of the Trempro 635 we originally used? My thoughts are to "skim-cut" the bubbles and then backfill those areas with additional sealant - but I am not sure if that sealant should be the Trempro 635 or the Trempro 644 RTV silicone. Will the Silicone stick to the original Trempro?

Any insights or help would be much appreciated!
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Old 09-17-2015, 08:42 PM   #2
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What did you use to clean/prep the surfaces? If it was alcohol, I'm afraid that you are in for a bitl of trouble, as alcohols inhibit the curing and bonding of polyurethanes like Vulkem.

I would never recommend the use of ANY silicone based product on ANY RV........ especially an aluminum one. The great majority of leaks that I have I have repaired were due to silicone use.

I would call the manufacturer and get their tech dep't. And describe your situation. I would think that you would get the BEST advice from them.


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Old 09-17-2015, 11:19 PM   #3
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Thank you Lew. We did not use alcohol to clean the area. We used acetone and 'Goo Gone'. Acetone did a great job of removing the Vulkem-like caulk that was there. They had also used silicone to seal. We got most of the silicone scraped up. The remaining came off with the use of 'Goo Gone'. After everything was up, we did a final through cleaning using the acetone again to remove any remaining oils that may have been left from the Goo Gone. Once everything was dry - we then installed the fan using the Vulkem.
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Old 09-18-2015, 12:45 AM   #4
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You might try removing the bubbling Vulkem, lightly sanding the area of the fan plastic, clean with carburetor cleaner ( I use tons of this) and then apply SikaFlex 221 over the area. Over the last 15 years, I have found it to be one of the best adhesive sealants available for general purpose use.
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Old 09-18-2015, 10:31 PM   #5
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Lew, I think we will be acting on your last suggestion. As I monitor the blisters that appeared on the Vulkem, they have not popped and they are not growing bigger. The Vulkem is solidly attached to the roof of the Airstream as well as around the perimeter edge of the Fantastic Fan flange. The only place it seems to easily come up is on the flat top lip of the Fantastic Fan flange. I believe your idea may take care of this. Thank you for your suggestion!
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Old 09-18-2015, 10:58 PM   #6
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Please keep us posted on your results.
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Old 10-10-2015, 04:14 PM   #7
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Update on our resolution of this problem. The air blisters that appeared in the Trempro 635 never "popped", so we let everything cure for 2 weeks. We then went back up, "sliced open each blister, and sliced off the excess blister walls with a razor blade. We used additional Trempro 635 to fill in the void created by the blister and smoothed everything out on top. We also lightly sanded the plastic lip of the Fantastic Fan to get the Trempro to adhere to that also. So - two weeks after that fix - no additional blisters popped up and no leaks! Thanks to all for you comments and advice!
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Old 10-10-2015, 07:02 PM   #8
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I need to comment on sealing Fantastic Fans with Trempro 644 (silicone). I just went through all of this and it was very frustrating.

I installed a fantastic fan about 5 years ago as part of my renovation. I used olympic rivets (a mistake), didn't use the factory supplied gasket and used Trempro 635 to seal. Everything worked like a champ and was water tight until a few years later when I started getting hairline cracks on the around the flange and up the base of the fan. If you search Airforums you will find the cracks are common on the older Fantastic Fan bases. I ordered a new base from Fantastic (~$12) and I can tell you that they now make the flanges a bit thicker.

So I took apart the old fan, moved the guts into the new base, and then got ready to reinstall. This time I decided to use stainless pan head screws and decided to once again not use the factory supplied gasket. I used Trempro 644 (silicone) since it was recommended by Vintage Trailer Supply when sealing Fantastic Fans. I ran a few beads around the bottom of the flange, set the fan, and then applied Trempro 644 over each screw head and ran a bead around the perimeter.

Well a few days later the dang thing was still leaking. I got up on the roof and I couldn't believe to find that the Trempro 644 wouldn't stick worth crap to the Fantasic Fan. It stuck great to the aluminum skin of the trailer, but just pealed right off (with no effort) from the fan base and screw heads.

So the next day I removed all the Trempro 644 and installed again (like I did years ago but used SS pan head screws) with Trempro 635. Do yourself a favor and DON'T USE Trempro 644 for Fantastic Fan installs.

I have it on my To Do list to go on VTS and review the 644 to let people know of my bad experiences.
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Old 10-10-2015, 07:27 PM   #9
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I agree with Modarch! I actually called Vintage Trailer Supply AND Fantastic Fan when we first had this air blister problem. VTS explained to me that Fantastic Fan had changed the formula they use in their plastic and this may have caused the bubbling/blistering. VTS told me that FF recommends using a Silicone based sealer, but they could not give me a further recommendation as to what to do now that I had used Trempro 635. I REALLY wanted to stay away from Silicone - so I called Trempro for advice.

The rep at Trempro I talked with explained that although a formula change at FF may have caused this (along with me using the gasket FF provided), another possibility was that the air blisters may have been caused because a by-product of Trempro 635 is a small amount of methane. Given the thickness I had applied, it was possible that the escaping methane may have caused the air blisters. Sounds plausible - but what do I know? I had thought we may have caused the issue by doing this on a 85 degree day, with 70% humidity, and a full sun day! Thats why we have a forum like this!

Anyways, as I wrote in the last post, once we sliced the blisters off and filled those voids with Trempro 635, all is now well. I DID get the Trempro 635 to adhere to the thickened FF base by scuffing that base first with some sandpaper.

Thanks again for all of the advice!
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