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Discussion Starter · #1 · (Edited)
polycarbonate window color, thickness, vendor?

Hello,

tomorrow I will change the acrylic windows on a Bristol 24 to polycarbonate. I was wondering what the appropriate thickness is? I can simply remove the acrylic and go to the store and have them mimic it. However, an opinion or two might come in real handy.

Also, what are the pros and cons of having the windows: clear vs transparent gray?

Finally, what is a good store online that will sell the sheets cut to spec? Tap Plastics is a local store that does it and I would go there unless there is a big price differential.

Thanks
 

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I've gone to local vendors and used the Lexan "Copper-Bronze" at 1/4" thick. They do develop a haze after time and I find that the products sold to clear and brighten automotive headlight covers work well.
 

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I replaced mine with 1/4 inch Lexan (Dark copper color). If I had it to do over I would use 1/2 inch Plexiglas with edges beveled to 1/4 to be flush with frame. The 1/2 inch could be stepped on by guest and Plexiglas holds up better in the sun than Lexan (So I was told after using Lexan).
 

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FWIW, acrylic is used to replace the lenses in hatches. While less prone to breaking, Lexan is too flexible. I would stay with acrylic if you are replacing large pieces for that reason.
 

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Which product is strong enough to stand on? This is a vague statement,- 'depends upon thickness and the area the material spans.



I regularly stand on this 3/8" Lexan (polycarbonate) at 205lbs; however, I do not stand on my other 1/4" hatches. Maybe they could take it,- I just don't! The 3/8" cover on this companionway slide covers an opening that is half the size (in area) of the Lexan cover.
 

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Can I sort of hijack this thread a bit, and ask if you buy acryllic or lexan, or plexi, what methods one can use to cut it? I've heard of using water, and installing a blade backward in a circular saw... Years ago I used a dremel and a reinforced cutting wheel (with dubious success, but it kind of worked, just required polishing the edges)...

3/8" lexan is some pretty stout stuff. Did you find it hard to drill through?
 

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I have used a router to cut it using the old piece of plastic as a template with the two sheets held together with double-sided tape. It is not too hard to work with normal woodworking tools.
 
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......................... 3/8" lexan is some pretty stout stuff. Did you find it hard to drill through?
I cut or drill polycarbonate with the protective adhesive paper coverings still on them and without difficulty. I's my understanding that Acrylic is known by several manufacturer's names like Lucite or Plexiglass and polycarbonate is known by manufacterur's names such as Lexan.
 

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Acrylic is harder therefore less capable of taking an impact than polycarbonate. Poly is softer, so it flexes under load and impact. Since they are both petroleum based, they are stupid expensive. 3/8 or 1/2 would probably be cost prohibitive. Working with it can be done with anything that will cut. But use a table saw with a fresh fine toothed carbide blade for best results. A router works fine but tends to heat up and fuse the scraps. If you drill, clamp a scrap of wood to the back and use a drill press if possible. The drill will probably pull and want to blow out the back. Sand the holes smooth. The scratches in the hole are what we engineering geeks call stress risers. Cracks will propagate out from them, given the chance. Some folks hit the holes with a torch to melt and fuse the scratches. I did that on the edges of mine. What size peice are you looking for?
 

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Discussion Starter · #10 ·
Got the polycarbonate from the local store. Had to go back a couple of times as they were making cutting errors. Question: the height and width of the windows are fine but the length is not flush to the edges. Seems a bit short but fits in the frame. Am trying to figure out if I need to go back and make a fuss and get them "exactly" to spec.

Also, is 5200 ok to use as an adhesive?

Thanks!
 

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

Thanks!
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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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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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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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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Discussion Starter · #16 · (Edited)
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.
 

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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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