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Old 01-04-2021, 01:10 AM   #1
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Best sealant for roof hatch?

I have a large 25 x 25in hole in the roof of my Gillig that the previous owner cut in for an RV hatch. I am improving the setup by making a "sleeve" that fits in the hole to give me a flat mounting surface for the Bowmar boat hatch I just bought. What would be the best sealant to seal the sleeve to the roof and/or the hatch to the sleeve?


It should be noted that the sleeve is not done. I will be welding a flange on top which will be the mounting surface for the hatch.
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Old 01-04-2021, 01:16 AM   #2
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Nice hatch

Sikaflex 521

https://usa.sika.com/en/industry/tra...ex-521-uv.html
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Old 01-04-2021, 06:42 AM   #3
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I did a similar "sleeve" or projection for my bus: https://www.skoolie.net/forums/f11/r...tml#post415593. I used Dynatron-550 between the sleeve and the bus roof, and Dicor butyl tape between the fan and the sleeve.
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Old 01-04-2021, 12:01 PM   #4
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3M 550 FC for us, & couldn't be happier. VERY strong, VERY flexible. Moisture-cured polyurethane. Whatever you do, don't use anything silicone.


For all I know, Dynatron 550 may be the exact same thing?? The thing I've learned about 3M products, however, is that while they provide detailed TDS's for their industrial products, like the 550FC above, they don't provide much info at all on consumer-grade products. I even contacted them asking for detailed specs on Dynatron & never got a reply.
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Old 01-04-2021, 12:17 PM   #5
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3M 550 FC for us, & couldn't be happier. VERY strong, VERY flexible. Moisture-cured polyurethane. Whatever you do, don't use anything silicone.


For all I know, Dynatron 550 may be the exact same thing?? The thing I've learned about 3M products, however, is that while they provide detailed TDS's for their industrial products, like the 550FC above, they don't provide much info at all on consumer-grade products. I even contacted them asking for detailed specs on Dynatron & never got a reply.
Since Dynatron-550 and 550FC are both 3M products I also assumed they were the same thing, but their ingredients are totally different.
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Old 01-04-2021, 12:44 PM   #6
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Good to know, musigenesis. Thanks for this. Color me surprised.

FWIW, I've found the 3M stuff you can find specs on almost universally less expensive than the consumer-grade products you can't. It's just less convenient to find.
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Old 01-04-2021, 03:55 PM   #7
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Bout to seal up my roof hatch. I've had great results with the dynatron 550 and I have a tube so that's my plan.
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Old 01-04-2021, 05:01 PM   #8
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Nice work. I like that your flange/plenum matches the curvature of your roof.
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Old 01-04-2021, 10:56 PM   #9
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Nice work. I like that your flange/plenum matches the curvature of your roof.
Thanks! It was a fair bit of work but worth it if it seals up and doesn't leak water.
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Old 01-04-2021, 11:02 PM   #10
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Well, it sounds like the Dynatron-550 is a favorite around here. Any idea how hard it is to remove if the situation arises? The previous owner sealed the old RV hatch with butyl tape and I am intrigued by the material. It doesn't seem like it compresses much but I was impressed by the ease of removal, even after 25 years. Any comments as to that?
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Old 01-04-2021, 11:16 PM   #11
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Originally Posted by paddywagon View Post
Well, it sounds like the Dynatron-550 is a favorite around here. Any idea how hard it is to remove if the situation arises? The previous owner sealed the old RV hatch with butyl tape and I am intrigued by the material. It doesn't seem like it compresses much but I was impressed by the ease of removal, even after 25 years. Any comments as to that?
For all its worth as a sealant, it's not really that hard to remove. A painter's tool (scraper thingy) and mineral spirits will do the trick.
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Old 01-04-2021, 11:24 PM   #12
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One good thing to keep in mind when working with dynatron is that when it starts to skin over you can use mineral spirits and a rubber-gloved finger to smooth it out and get a really nice finish.

But smooth it out first so as not to get any solvent between the dynatron and the surface you’re applying it to.
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Old 01-05-2021, 12:15 AM   #13
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Quote:
Originally Posted by musigenesis View Post
I did a similar "sleeve" or projection for my bus: https://www.skoolie.net/forums/f11/r...tml#post415593. I used Dynatron-550 between the sleeve and the bus roof, and Dicor butyl tape between the fan and the sleeve.
Out of curiosity, why use Dynatron on the roof but then butyl on the fan?
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Old 01-05-2021, 06:15 AM   #14
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Out of curiosity, why use Dynatron on the roof but then butyl on the fan?
The installation instructions for the fan called for using butyl tape and I randomly had a bunch of it lying around. If left to my own devices, I would have just used the 'tron.
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Old 01-05-2021, 08:55 AM   #15
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Quote:
Originally Posted by paddywagon View Post
Well, it sounds like the Dynatron-550 is a favorite around here. Any idea how hard it is to remove if the situation arises? The previous owner sealed the old RV hatch with butyl tape and I am intrigued by the material. It doesn't seem like it compresses much but I was impressed by the ease of removal, even after 25 years. Any comments as to that?
Its basically the same/similar to the factory seam sealer. Not too bad, it never FULLY hardens and it isn't really an adhesive.
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Old 01-06-2021, 12:24 AM   #16
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As popular as this Dynatron stuff is, it seems a little too permanent for my application. It should be said that for this application I do not need an adhesive/sealant, just a sealant. The sleeve will be secured to the roof with 8 bolts and the hatch to the sleeve with its screws.


I am leaning towards a marine sealant, which seems appropriate since I am fitting a boat hatch. I'll do a bit more research and report back.
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Old 01-06-2021, 07:10 AM   #17
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Quote:
Originally Posted by paddywagon View Post
As popular as this Dynatron stuff is, it seems a little too permanent for my application. It should be said that for this application I do not need an adhesive/sealant, just a sealant. The sleeve will be secured to the roof with 8 bolts and the hatch to the sleeve with its screws.


I am leaning towards a marine sealant, which seems appropriate since I am fitting a boat hatch. I'll do a bit more research and report back.
dynatron 550 isn't an adhesive. just a sealant. Its automotive body seam sealer.

Have you thought about lap sealant?
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Old 01-06-2021, 09:46 AM   #18
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Dynatron seems less permanent than sikaflex. But I’d still use Sika UV resistant sealant because I think it will withstand the elements better. Still, both seem pretty good. I used Dynatron to fill a 1/4” wide foam-backed joint where the bus body joins the cutaway, then I painted it. You wouldn’t know it wasn’t from the factory that way. I had some initial adhesion issues on the first try but after scuffing the paint with 220 grit it’s fine.
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Old 01-06-2021, 09:52 AM   #19
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You can actually get a perfectly smooth finish out of Dynatron by rough-smoothing it with your finger and then giving it a good misting with mineral spirits from a spray bottle. The mineral spirits form a perfectly smooth skin and then evaporate.
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Old 01-06-2021, 09:54 AM   #20
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You can actually get a perfectly smooth finish out of Dynatron by rough-smoothing it with your finger and then giving it a good misting with mineral spirits from a spray bottle. The mineral spirits form a perfectly smooth skin and then evaporate.
Yep, thats it.
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