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Old 11-18-2017, 09:17 PM   #1
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How to seal Leaking Windows?

Hey all. Our windows are leaking like sieves! It's especially bad in heavy, continuous rain. They've been removed and reinstalled by the previous owner, but it didn't seem to really "take". He used silicone caulk and there was weatherstripping around the perimeter. Not sure exactly where the water is coming in, but I've tried sealing the outside of the windows and at this point I think I'm ready to just pull them, scrape off the old, and reseal them. I did this with one window today and it wasn't too terrible of a job. So, a couple quick questions.

What sealant should I use? From what I've read, my main choices seem to be Butyl Tape (or gutter/butyl caulk?) Thermoplastic Elastometric Sealant or possibly a Polyurethane Window/Siding Sealant.


Do I need weatherstripping? The face of the window-frame mates with the rib-frame of the bus. I'm pretty sure it was a flush-mating sort of fit. The bottom of the window rests on the bus frame.

My gut tells me I should scrape out all of the silicone and weatherstripping (to have clean metal surfaces) and slather a TON of sealant around the perimeter, with a nice heavy bed of sealant for the bottom of the window to set into. I don't care how many tubes of sealant I use, I just don't want to have to do it twice! I don't know if I need weatherstripping or not.

We can't really move forward with our plans until we get this thing water tight.

Thoughts, suggestions, advice? What have you guys done, what has worked for you?

Thanks,
-Drew
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Old 11-18-2017, 09:23 PM   #2
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Take the windows out, clean all the crappily applied sealant off, apply new seam sealer.
3M Dynatron 550 is what I'd use.
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Old 11-18-2017, 09:27 PM   #3
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Yeah, I wouldn't let silicone anywhere near the bus.

Once it's there, be very careful to remove all traces or nothing else will stick.
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Old 11-19-2017, 07:41 AM   #4
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Quote:
Originally Posted by EastCoastCB View Post
Take the windows out, clean all the crappily applied sealant off, apply new seam sealer.
3M Dynatron 550 is what I'd use.
Weatherstripping? Yeah? No? I'm thinking not.

Also, at the bottom of the window and especially in the bottom corners is where the water seems to be coming in. Any idea how to deal with this? I'd planned on using a generous amount of sealer to embed the bottom window frame. Is this a sound idea?
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Old 11-19-2017, 10:26 AM   #5
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Butyl rubber caulk tape will be your most affordable option. It is inexpensive and easy to use.

When you take the windows out you will need to make sure every vestige of the silicone is removed or you will be doing the whole process over again.

I can't tell very well from the picture but if your bus body is an AmTrans from the mid-'80's to the early-'00's the windows used by AmTrans were pretty poorly built and installed. We had some brand new AmTrans buses in the mid-80's that had windows that leaked from day one.
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Old 11-19-2017, 10:39 AM   #6
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Originally Posted by cowlitzcoach View Post
Butyl rubber caulk tape will be your most affordable option. It is inexpensive and easy to use.

When you take the windows out you will need to make sure every vestige of the silicone is removed or you will be doing the whole process over again.

I can't tell very well from the picture but if your bus body is an AmTrans from the mid-'80's to the early-'00's the windows used by AmTrans were pretty poorly built and installed. We had some brand new AmTrans buses in the mid-80's that had windows that leaked from day one.

The bus is a 1996 Amtran. There was weatherstripping on the bus frame and I'm not sure if that was factory-installed or added later. It may have been butyl rubber tape, I'm not certain.....it had an adhesive backing that made it look like regular weatherstipping tape though.

Any other tips, Cowlitzcoach, on resealing these things especially the bottoms and bottom corners?
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Old 11-19-2017, 01:11 PM   #7
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I was just thinking about my window leaks as I logged in...

I must pass on this advice from an auto body-repair pro. As mentioned above, never use silicone to seal your bus, or any metal surface for that matter.

Silicone absorbs moisture from the atmosphere, and holds it internally. Sure it repels volumes of water, but even when not raining, it is holding water against the surface it adheres to. If the surface is metal, it will corrode/rust. This is also why the silicone water sealant in bathtubs always turns black with mold stains. The mold is in the silicone, not on it (spray it with hydrogen peroxide @ $1.50/bottle using a atomizer screw-on top spray-head after each shower, and it will turn white again).

I learned that unfortunately after I re-sealed the windows in my 1977 Dodge Tradesman hightop conversion van with acrylic-silicone window-sealant for homes. (Love the styling on that old one...) I was told use only black urethane window sealant. Polyurethane I think is more adhesive and firmer, and will be harder to remove in the future, but I don't know for sure. Maybe good for house siding and window frames, but vehicles vibrate and flex, and tend to be dismantled and reassembled in the future, whereas houses are gutted and all-new materials are used.

Also, polyurethane glue for wood can cure faster and stronger when the surfaces are exposed to water and damp. Does that mean polyurethane is also water-absorbent like silicone? I don't know.
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Old 11-19-2017, 01:35 PM   #8
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I do know that most Urethane glues (like Gorilla Glue) are rated as 100% waterproof as it is CG approved for use "below the waterline".

But the best material I have found for long term sealing is OEM grade automotive "Seam Sealer". Any number of brands available, I use the 3M variety. It stays flexible, will last for many decades and is totally waterproof. Sticks like crazy to just about anything but check the manufacturer's specs for any particulars.
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Old 11-19-2017, 01:41 PM   #9
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Funny, I was thinking about my leaking windows, too. Good information - I'm going to use the seam seal / 3M stuff.
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Old 11-19-2017, 01:57 PM   #10
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The 3M is not cheap but it works. It is the same material as what Detroit & Japan use to hold cars together and weatherproof all metal to metal seams on their cars. Also sticks perfectly well to glass, but most use a slightly different formulation for windshields and such that is more easily removable.

Just make sure to get any surfaces absolutely clean first. Just like painting, prep is critical to success. Alcohol as a final wipe down is good but again, check the manufacturer's recommendations.
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