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post #11 of 17 Old 06-27-2014
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Re: polycarbonate window thickness?

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Originally Posted by andyselzn View Post

...Also, is 5200 ok to use as an adhesive?

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Dow Corning 795 is a good sealant to use for this kind of thing. I wouldn't use 5200 for this.

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post #12 of 17 Old 06-27-2014
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Re: polycarbonate window thickness?

andy, 3M makes special adhesive for polycarbonate, 3M 4200 as I recall. West Marine actually STOCKS it, along with their own version, and oddly enough the 3M product is also way cheaper than the WM version.

If you do not use an adhesive that specifically is designed for polycarbonate, it WILL let go within the year.

All the plastics do suffer from thermal expansion, so if it is "short" now and the temps are 60F, I wouldn't worry, I'd let the sealant fill it. But if temps are 90F and it is short...it is only going to get shorter, so remind them "Measure once cut twice." [sic]

Kinda depends on how long the plastic is, and how big the gap is. You can look up the expansion specs online for whatever brand and grade of poly it is, it can easily be 1/16" per foot for the range of freezing to heatstroke.
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post #13 of 17 Old 06-27-2014
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Re: polycarbonate window thickness?

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Originally Posted by andyselzn View Post
Also, is 5200 ok to use as an adhesive?

Thanks!
Noooooooo!!!!!!!!!!!!

There are very few uses for 5200 on a boat. Do yourself a favor and don't use it for anything. 5200 is very permanent, and should require a special license to use! I don't understand why people want to use this stuff for everything.
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post #14 of 17 Old 06-27-2014
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Re: polycarbonate window thickness?

DO NOT use 5200. Read this.

Which Sealants To Use
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post #15 of 17 Old 06-29-2014
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Re: polycarbonate window thickness?

Never use a urethane base adhesive/sealant with poly or acrylic. It can/will case plasticizer migration and cause the glazing to craze. This could be anything from a cloudy appearance to spider cracks. As far as expansion goes, figure on 1/8 " per 3 feet per 100 degrees for clear. Gray or bronze is twice that.
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post #16 of 17 Old 06-30-2014 Thread Starter
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Re: polycarbonate window thickness?

Dow 795 is a Silicone based compound so it will work for polycarb (lexan) to fiberglass or metal.

4200 is a polyurethane and will work for the metal to fiberglass. Or should it be Butyl tape instead?

Seems like I need both these. The first to fill the spaces between the glass and the brackets and the second to place around the frame. I will be using screws to screw them back on even though several posts online suggest not using them.

Last edited by andyselzn; 06-30-2014 at 09:14 PM.
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Re: polycarbonate window thickness?

Screws:
Andy, go look it up directly with the source. GE is one of the prime manufacturers who have architectural installation sheets online. There is no question or issue or debate about screws. If you simply drill a hole and snug the glazing up with a screw, you will destroy it as it expands and contracts and, pinned down by the screw, crazes and cracks.

"Simple" use of screws guarantees plastic glazing will self-destruct.

OTOH, correct use of screws (bolts, etc.) is perfectly acceptable. You must (MUST) drill the hole in the glazing large enough so that it will allow full expansion and contraction without the glazing hitting the screw. The hole has to be big enough so the glazing can literally be lifted off. Then you add fender washers or similar trim under the screw head, and torque them down gently so that the glazing is left to slide back and forth, under the washers, without being forced up against the screws.

Every glazing manufacturer specifies the same requirements.
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