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Old 29-07-2006, 14:00   #1
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Techniques to rebed dead lights (windows)

Its time to rebed the dead lights (windows) on Sunspot Baby. When we bought her, she leaked a little when it rained a lot. Now she leaks a lot when it rains a little.

I have read two other threads on this forum, one on “sexy windows” and “the best sealant for beding”. Lots of good information there, but I need a little more advice.

Our dead lights are Lexan or a Lexan wannabe. They are attached with numerous flat head screws around the periphery. I want to simply remove, clean, and rebed, without replacing. That means I will resintall using the screws.

I am interested in techniques to keep from squeezing all the sealant out when I first install. Someone suggested tape as a shim, but I don’t recall if they defined the type of tape to use. I saw a web site that suggested a stainless washer on each screw. That would seem to limit your ability to tighten down against the “gasket” formed by the sealant after cure.

Any suggestions or experience (good or bad) is appreciated.

George
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Old 29-07-2006, 14:26   #2
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You can do it this way. Place your sealant around and install as per "sexy windows", but do not screw them all the way home. Once the sealant has begun to cure, then apply extra force to the screws. If you don't want to actually bond to the lexan, then I would use a weather seal strip instead of the sealant, OR you apply the sealant and allow to skin, THEN screw the lexan on.

Another question you may want to test out, is how strong those windows are now. Lexan losses it's strength over time and especially with detergents and especially bonding agents. It becomes brittle. You may want to give a small one a smack with a hammer and see how easy it cracks. If it breaks, you want to look at replacing them all. If it doesn't break, you should be fine.
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Old 29-07-2006, 14:52   #3
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Good info Wheels, presuming the Lexan is still in good shape, I would whole heartedly recommend Sika flex products for re-bedding the plastic.

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Old 29-07-2006, 14:57   #4
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Sikaflex yes, products no. There is only one sikaflex product suitable for this that contains the UV stabilisers. Remember to use the sikaflex primer first
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Old 29-07-2006, 15:07   #5
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Righto!! It's the primer that makes Sika different!

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Old 29-07-2006, 15:30   #6
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Sikaflex 295UV

Direct Glazing Adhesive for polycarbonate acrylic use with sika primer 209, as a sealant for glass, ceramics, metals, plastics, fiberglass, amany types of paint. Sika 295 UV is a fast curing, one-component, flexible, high performance polyurethane-based adhesive for bonding and sealing of windows and portholes. Sikaflex 295 UV is suitable for all types of organic (PC, PMMA) windowpanes. Its high degree of UV resistance also allows the use of the system as a weatherproof sealant.
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Old 30-07-2006, 00:34   #7
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It's also essential that the correct adhesive is used, because any adhesive not made for Polycarbonates can attack the stuff and make it become brittle.
I have just recently done some training on Polycarbinate for a totaly different requirement, being high impact saftey lenses. I was amased at the safety issues and just how easy it was for the lens to degrade in a very short time if they are not taken care of correctly. Even then, I have to replace the lens every 12mnths to maintain the full impact protection.
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Old 30-07-2006, 06:42   #8
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Since the Sikaflex is a polyurethane-based adhesive I was concerned it would harden, and thus not flex with the boat resulting in cracking and new leaks.

Does it remain plyable?

George
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Old 30-07-2006, 13:23   #9
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Yes it remains plyable and will flex easily and take up expansion and contraction due to heat. Or if I put this another way, if the sealant isn't plyable enough, the flex in your boat is waaaay too much and I would be worrying about other things way befor windows leaking:-)
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Old 30-07-2006, 15:39   #10
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Assuming of course that it is polycarbonate. Many, perhaps MOST, boaters presume they have poly when they've just got acrylic. I suppose the simplest way would be to get a bottle of fusion solvent for one that won't work on the other, and make a drip test?
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Old 30-07-2006, 22:26   #11
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Or hit it with a hammer and see which one breaks easier ;-)
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Old 31-07-2006, 05:06   #12
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I don't suppose it really matters whether it is poly or acrylic does it? Sika indicates the 295 works with either.

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Old 31-07-2006, 11:53   #13
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Wheels, I like hammers too but that would ruin a perfectly good deadlight. Both might simply show conchoidal fracture if hit "properly", making the hammer a moot point.

George, if Sika295 is what you are using and the same prep and goo work with both...then it may be immaterial.

I know someone who said "Oh, that's Lexan, don't worry about that" while we were replacing portlights. I went "dink" with a claw hammer and right through it. He now takes greater care to make sure a spinnaker pole won't hit the new portlights, and go through them equally easily. (It would be a hard shot to make on purpose, but we all know the Gods make those shots every day.)
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Old 31-07-2006, 13:19   #14
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Yeah In like Gods sense of humour. Just when we think something is indestrctible against the "higher powers", he sticks his finger through it to show us our place in greater scheme of things.
If the guy broke his Lexan like that, then it is probably due for replacement. That's what happens to it. It becomes brittle and weak.
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Old 31-07-2006, 13:25   #15
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Wheels-
He "knew" they were Lexan, because like most boat owners today, somehow he figured something good would have been used. Point was though, they were not Lexan. Most "marine" glazing is just acrylic, from what I gather partly because of cost and partly for better scratch resistance. With a few notable and pricey exceptions.
I don't know why, it just seems like "Lexan" is a sexier word so people have decided to use it, with no concept of what it means.
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