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Old 04-20-2015, 08:55 PM   #1
Skoolie
 
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Sealing windows, caulk or butyl tape?

I'm in the process of stripping down the bus, and before I paint it I'm going to pull out all the windows and refinish them. When I put them back in, is it better to use butyl tape or should I go with some sort of caulk (if so, which one)?

Thanks!
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Old 04-21-2015, 11:27 AM   #2
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Originally Posted by Piersg View Post
I'm in the process of stripping down the bus, and before I paint it I'm going to pull out all the windows and refinish them. When I put them back in, is it better to use butyl tape or should I go with some sort of caulk (if so, which one)?

Thanks!
Looks like you have a very similar bus to mine. Your windows are held in by the little metal tabs that are screwed in on each side, yes? What I did on mine was pull out all the windows. If you weren't sure how, the best way is to undo all the little metal brackets, score the perimeter inside and out of each window frame with a utility knife to break the current seal, then pull the window in from the top and lift it out.

The stuff that seals it from the factory is some super gooey rubber stuff that at least on mine, was still tacky ~17 years later. I scraped each window frame as well as the frame on the body of all the gooey stuff, bent the little metal tabs so they had a bit more tension on them when put back in, reinstalled the windows and sealed the perimeter inside and out with high grade silicone. Make sure it is pure silicone rated for outdoors, UV exposure, etc. I recommend doing it this way because it got rid of the super loud window rattles and shakes when driving that these buses always have. I probably used 12 tubes of silicone doing this, maybe more. PM me for questions!
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Old 04-21-2015, 01:57 PM   #3
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I, personally, would stay away from silicone. If ever the window needs to be removed it will be a pain in the arse to clean and re-caulk. There are some very good thermoplastic rubber sealants out there that seal great, stretch far, are made for extreme temperatures AND can be removed in one long piece when the time comes. I experimented with many sealants before settling on Mulco Supra Expert for sealing metal-to-metal.
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Old 04-21-2015, 03:04 PM   #4
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Thanks for the info. So far I have one vote for Silicone caulk and one vote against it. I'm sort of leaning towards using Butyl tape because I can get it pretty cheap and it is a little less messier, however I am keeping my options open.
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Old 04-21-2015, 03:28 PM   #5
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My 1991 Blue Bird school bus had gray stuff around each window that looked like butyl to me. I now have a 2000 Blue Bird transit bus with a different kind of windows; these were installed with a heavy (stiff) black open cell foam plus gray stuff that looked like butyl.

Perhaps it's due to amateur workmanship such as failure to clean the surfaces with alcohol -- but I've seen many more silicone caulk fails than butyl fails.
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Old 04-21-2015, 04:31 PM   #6
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My question about butyl tape is this: On my bus the metal that the bus window connects with is perpendicular to the window frame. Does butyl tape work effectively at sealing two perpendicular pieces of sheet metal? It works great when squashed between two parallel surfaces, but my guess is that the sheet metal coming into it at a perpendicular angle would act like a knife going through it. Caulk type sealants are typically meant specifically for perpendicular surfaces.

If the bus originally came with butyl tape then it must be ok, though. Other buses may be built differently.
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Old 04-21-2015, 05:23 PM   #7
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There are a couple of varieties of automotive Seam Sealer that work like gangbusters. The urethane type comes in several colors, is totally waterproof,never dries out, is paintable in 30-45 minutes, won't shrink or crack and is unaffected by UV and chemicals. And while it is tough stuff can usually be "peeled" or scraped off without too much hassle. The 3M variety is just one of several that are OEM speced by the automakers.

There is also a heavy duty two-part epoxy variety that is a different animal, but very useful too.

PS...Butyl tape is great too, but works best between two smooth, flat surfaces. If there are any variances, the fluid application is better at filling in any voids.
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Old 04-21-2015, 06:14 PM   #8
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Tango said it best.

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Old 04-21-2015, 06:40 PM   #9
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hmm, so now I need to research 3M Automotive Seam sealer!

Thanks for the info guys!

Now, does anybody have a good source for roof hatches? Mine was leaking and when I took it off I found 5 layers of old caulk covering inch long rusted out holes on the edges of the pop up vent. I cleaned it off and recaulked it, but it needs to be replaced.
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Old 04-21-2015, 09:13 PM   #10
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IMO I don't feel roof hatches are needed for a privet conversion. I will be sealing mine with a sheet of steel.

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