Lexan/polycarbonate vs acrylic - Page 4 - SailNet Community
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post #31 of 44 Old 08-18-2014 Thread Starter
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Guys, Dow's data sheets say that 795 is suitable for use on GLASS and aluminum. It is not stated anywhere on their data sheet that it can or should be used on acrylic or fiberglass. It is a silicone rubber sealant, and traditionally those ALWAYS peel off acrylic and release after they've worked for a while.

So...Try 3M's 4000 adhesive, which is designed for polycarbonate and acrylics. Or something else. If the data sheet does not expressly say you can use it with acrylic--it will fail.

VHB tape was just on the history channel, as "one of the world's ten strongest products". But again, that's subject to following the directions.
The one I read said "plastics".. https://www.google.com/url?sa=t&sour...JIXPWtL2ohPDyQ

I ordered a tube, but somehow it being Silicone slipped my mind. I have some long acrylic Windows on my boat that I'm about to install finally. I didn't want to use silicon so I'll check out that GM 4000.
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post #32 of 44 Old 08-18-2014
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Re: Lexan/polycarbonate vs acrylic

795 is not bathtub sealant but a structural silicone adhesive and probably the best choice for plexiglass ports. Especially in conjunction with the Vhb tape.

Ever notice that there are not any production boats of any size using fasteners for plastic ports now?

And as posted above it is usable on plastics.


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Re: Lexan/polycarbonate vs acrylic

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795 is not bathtub sealant but a structural silicone adhesive and probably the best choice for plexiglass ports. Especially in conjunction with the Vhb tape.

Ever notice that there are not any production boats of any size using fasteners for plastic ports now?

And as posted above it is usable on plastics.

OK thanks, I'll use it then haha! Works for me, about to pick the glass up now.
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Re: Lexan/polycarbonate vs acrylic

"Plastics" would include PTFE and polyethylene, both notoriously hard to bond to. Adhesives which form a strong and permanent bond to plastic glazing materials, which may be styrene, acrylic, or polycarbonate, usually say so in express terms.

Considering the price of a phone call versus the price of a failed glazing job, I'd call the maker rather than wait for it to fail, and then have my lawyer call their lawyer about the definition of the term "plastics".
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Re: Lexan/polycarbonate vs acrylic

From Select Plastics, the largest hatch rebuilder in the world. Home


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Re: Lexan/polycarbonate vs acrylic

Can anyone tell me what thickness of acrylic pane should be used for windows about 8" x14"?
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Re: Lexan/polycarbonate vs acrylic

Just a couple comments

1) I've used VHB tape in a bunch of places. It's not suited for everything but it's good stuff. It's currently holding my VHF to the cabin ceiling among a other things.

The easiest place to buy it from is McMaster, which sells at least 2 dozen versions of it. Always in stock.

Home depot also carries a few consumer versions marketed as exterior mounting tape.

2) Lexan really does scratch up easily. I just made the mistake of trying to clean my lexan hatchboards with a scotch pad and I fogged it up by putting tiny scratches in it (I didn't notice at first because it was so dirty the scotch pad was still making it better). I'd care except there are so many other scratches the new ones don't really register.
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Re: Lexan/polycarbonate vs acrylic

asdf-
Odds are those will buff out with the appropriate polish.

gs-
What thickness you "should" use depends on what you want to keep out. Spinnaker pole breaks loose and torpedoes the portlight? That's going to take more strength than fair weather splashing. Broach the boat and have a 20-foot wave drop onto the portlight? You'd be surprised at how much force that can generate.
For a no-numbers practical compromise, 1/4" acrylic is fairly common and affordable. That "should" keep a lot of stuff out, including the occasional crew walking on it during the broach. See if your seller has any grade of acrylic that is uv- and scratch-resistant for exterior glazing, not just the stuff they make napkin holders out of.
FWIW the great Fastnet investigation concluded that portlights should have the same failure strength as the structure they are set into. That could mean 1/2" or more, if you're planning for those conditions.
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post #39 of 44 Old 10-03-2014
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Re: Lexan/polycarbonate vs acrylic

I want to replace my deadlights as well, and there is a log of very good information in this thread. Thanks to all who have contributed.

My Precision P23 has Lexan deadlights about 51 inches long, with screws around the perimeter. I'd like to replace them and leave off the screws, using 3M VHB and Dow 795.

I might have missed an answer to the question about having a slight curve to the window. Will acrylic work? Can I use the no-screw flush mount method as described in the Sail article and by others here?

The last photo below is taken edge-on, and shows the amount of curve.





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Re: Lexan/polycarbonate vs acrylic

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asdf-
Odds are those will buff out with the appropriate polish.
Like what kind of polish?
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