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post #21 of 37 Old 02-25-2009
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I just replaced my two hatches with 1/2" Lexan. I sprang for the top of the line UV resistant scratch proof stuff, which is absolutely bulletproof. A friend owns a sign shop, and even with friend pricing I still paid $600 for the 4x8 sheet! Supposedly, I can get 10-20 years out of this lexan without crazing. I can now make a transparent single piece slat that is stronger than my wooden slats. It will be great for watching bad weather while staying dry.
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post #22 of 37 Old 03-26-2009
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Through Bolt or Self Tappers

Re: Surface mounted fixed portlights.

I would imagine through bolts would be the strongest.

Do people have an opinion on whether using a black caulking compound equiv of 5200 and self tapers every 8 inches would be sufficient?

Last edited by matt2; 03-26-2009 at 01:27 AM.
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post #23 of 37 Old 03-26-2009
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Don't use 5200 on a boat. It really has little use on a boat. It is far too strong and permanent an adhesive for anything that may need replacing.

Self tappers are a bad idea in fiberglass. Fiberglass is rather brittle and doesn't take screws well. You're really much better off through-bolting.
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Re: Surface mounted fixed portlights.

I would imagine through bolts would be the strongest.

Do people have an opinion on whether using a black caulking compound equiv of 5200 and self tapers every 8 inches would be sufficient?

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post #24 of 37 Old 03-26-2009
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I agree; 5200 has no real use. Also, do not use Thiokol or its equivalents with lexan - use silcone which also happens to be easier to work with. Self tappers? No way. Pre drill holes in the lexan and then srew them into whatever is under it. You could throuh bolt too if appropriate/possible.
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post #25 of 37 Old 03-26-2009
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I would never use 5200 to seal hatch, I always use 3M marine silicone. However, 5200 is AMAZING for patching torn sails. I have a mainsail that has torn completely across over a year ago. I glued a patch over the entire rip with 5200 and it still holds perfectly. I had it out in 30-40 mph winds this weekend with the full sail up, and had no problems. If you plan well, you can even make it look nice(I don't). I always keep old sail scraps and 5200 for emergency repairs.
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post #26 of 37 Old 03-26-2009
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I agree

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Don't use 5200 on a boat. It really has little use on a boat. It is far too strong and permanent an adhesive for anything that may need replacing.

Self tappers are a bad idea in fiberglass. Fiberglass is rather brittle and doesn't take screws well. You're really much better off through-bolting.
I agree, I have never been happy with it, though I think it is probably strong enough. I may redo one window and see how it goes.

This is one of the things I got a "professional" to do when I first got the boat.
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post #27 of 37 Old 03-26-2009
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BTW, when you drill holes in the Lexan or Plexiglass, don't forget to countersink the holes ON BOTH SIDES so they don't become a starting point for nasty stress crack.

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post #28 of 37 Old 03-26-2009
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Go ahead with the 3/16 lexan. Lexan is very, very tough. Once it's on, I doubt you could break it with a hammer. If it's plexi, on the other hand, you need to go thicker.

I have folded lexan in half in the vice without breaking it.

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post #29 of 37 Old 03-26-2009
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Lexan is predrilled

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Originally Posted by cutterorient View Post
I agree; 5200 has no real use. Also, do not use Thiokol or its equivalents with lexan - use silcone which also happens to be easier to work with. Self tappers? No way. Pre drill holes in the lexan and then screw them into whatever is under it. You could throuh bolt too if appropriate/possible.
Yes the lexan is predrilled, but I believe self tappers were used into the fibreglass.

I think I will try replacing one of the windows and in the process it will become clear whether it has sufficient adhesion and whether the other windows need replacing.

The lexan overlaps the outside of the windows by about 4 inches all around, so quite a bit of surface area attachment.

I read somewhere that if the lexan overlaps the fiberglass and you don't want to see all the goop behind the lexan then you should paint the back of the lexan where it overlaps. But I am not sure what paint to use?
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post #30 of 37 Old 03-26-2009
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Matt, call GE's toll free number. Ask the lexan ("structured plastics") division and the silicone sealants division if you can use silicone seal to glue Lexan to fiberglass.

I'm fairly certain they will all tell you NO WAY. Silicone products simply do not bond to Lexan, you not specific adhesives and often primers for them, or the Lexan will rather quickly unbond from the adhesive.

A couple of free phone calls will save you from a major redo.
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