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Old 06-03-2016, 21:23   #46
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Re: Which sealant for Lexan

"UV resistant Lexan is available in thicknesses greater than 1/4", but most often only in full sheets as I understand"
Aside from "the cheapest grade" of any plastic glazing, almost every other grade and color is only sold by the full sheet. he suppliers, who will often waterjet or laser cut the sheet any way you want, sell the full sheets so much cheaper than the local plastics place sells "per foot" that it is still cheaper in the long run. They don't want to screw around with bargain bins and partial sheets that can sit around for a year or more until someone wants anything besides "plastic" for their napkin holders.(G)


You want milk white translucent plexi? That's by the sheet. Brown? Gray? Mirrored? Again, often by the sheet. Lexan, Plexi, Makrolon...If you find a place that stocks different grades and types, and is willing to talk about it up front, odds are they're price competitive with the local household plastics place.


As to the choice of hatchmakers...I don't doubt they have their reasons. "Built to a price" is often a primary reason, and one that vendor vehemently deny, in any mass-market product. But at that point, they also get into extruded versus cast products. It is more than a simple choice for a particular simple reason.


If I was building a racer or an express cruiser and I wanted to get the weight out...I can tell you that I'd go with lexan instead of plexi right away to shed maybe 2/3 of the weight of the glazing material, at the same strength. If I wanted to build a mass-market weekender...just the opposite.


And a couple of bottles of polish, up to 3M's 3000-grit grade, will keep the surface nice and shiny if you scuff it up. Regardless of what plastic it is.
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Old 06-03-2016, 21:55   #47
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Re: Which sealant for Lexan

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Originally Posted by hellosailor View Post


As to the choice of hatchmakers...I don't doubt they have their reasons. "Built to a price" is often a primary reason, and one that vendor vehemently deny, in any mass-market product. But at that point, they also get into extruded versus cast products. It is more than a simple choice for a particular simple reason.


If I was building a racer or an express cruiser and I wanted to get the weight out...I can tell you that I'd go with lexan instead of plexi right away to shed maybe 2/3 of the weight of the glazing material, at the same strength. If I wanted to build a mass-market weekender...just the opposite.
Their reasons are durability and clarity. Plexi will remain clear long after lexan starts to get hazy.

With a hatch the Lexan ones are not lighter. Bomar is the only company using Lexan as far as I know, and only on a few models. Most of their hatches are Plexi. Their Lexan hatch about 25% heavier than the comparable size Plexi hatches they make. Crossbars to stop the Lexan from flexing when stepped on and breaking the seal add weight.



Lewmar (all hatches including the Ocean series, probably the most common hatch on larger sailboats) are all Plexi as are all the others with the noted exception.

As far as buying a full sheet - that depends how much is needed. I did find 1/2" Lexan with UV resistant coating in 4' x 4' sheets at a price of $724 US.
http://www.eplastics.com/Abrasion_Re...arbonate_Sheet

Plexiglas doesn't require a coating to resist UV. A friend has a Spencer 35 built in 1964 (came off the line next to Hal Roth's Whisper) and the original Plexi ports, quite large, are still clear with a few marks from use over the years.
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Old 07-03-2016, 00:40   #48
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Re: Which sealant for Lexan

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Only GE (maker of Lexan) approved stuff is SCS 2000 SilPruf. 5200 is a big mistake read the tube.
Used scs2000 no leaks no peeling.
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I did quite a bit of research in the late 80's and used GE SilPruf also with good results. At that time, I believe it was the only thing available. When I bought my HR 35, it was all acrylic, non-opening ports that I have replaced with SS framed and safety glass. I have 2 long ports left to replace. I will replace those with acrylic. They have improved acrylic quite a bit and regular silicon can be used on them.
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Old 08-03-2016, 20:08   #49
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Re: Which sealant for Lexan

Here's a pic of the 3/8" Lexan in my Bomar hatch. This is the center of the hatch where the square hole in the canvas for the old vent leaves the Lexan uncovered, for almost six years.

The area above the black crossbar is covered and the area below is exposed. I wiped the dust away with a wet finger to see the condition of the Lexan in the exposed area. Photo taken in direct sunlight, reflected in the picture.

I think the condition is good for six years of constant exposure.

I have never cleaned the hatches with anything. When I scrub the deck the canvas stays on. Only rain cleans the lenses.

As I said the material was cutoffs from a skylight company. Perhaps that explains the apparent durability. I doubt I will be replacing them anytime soon.
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Old 08-03-2016, 23:52   #50
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Re: Which sealant for Lexan

Fair prices on Lexan in half sheets can be found here.

.472"(12.7mm) x 48" x 48" Lexan™ Polycarbonate Sheet | U.S. Plastic Corp.

4' x 4' x 1/1" $350
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Old 09-03-2016, 07:45   #51
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Re: Which sealant for Lexan

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Fair prices on Lexan in half sheets can be found here.

.472"(12.7mm) x 48" x 48" Lexan™ Polycarbonate Sheet | U.S. Plastic Corp.

4' x 4' x 1/1" $350
Doesn't have UV protection so not a very long service life.
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Old 09-03-2016, 09:12   #52
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Re: Which sealant for Lexan

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Doesn't have UV protection so not a very long service life.
The Lexan in my old forehatch lasted 35 years until I replaced it due to crazing. US Plastics also sells the UV protected Lexan and I made Sunbrella covers for my deck hatches.

I think the only thing better than Lexan is glass.
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Old 09-03-2016, 09:22   #53
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Re: Which sealant for Lexan

I replaced all my aluminum frame hatch plastic with Lexan in 2009, used GE SCS 2000 Silpruf sealant, absolutely no problems more than 6 years later. I had the Lexan cut and supplied by an outfit in Annapolis I think, and they recommended the GE product as the only product to use. I did enough research to vet the recommendation, and I'm glad I took the advice. It was $20 per tube, but I didn't want to cheap out and be worried about premature failure. What I wanted was exactly what I have now - 6 years of leak free performance. BTW, those hatches went from Annapolis to Florida to the Bahamas to Texas to Florida to Annapolis to Florida to the Bahamas to the E. Caribbean as far as Grenada, then back to Florida and then Texas. All without hatch covers, lots of UV, etc. The Lexan/GE sealant is one of the few success stories in that cruising.
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Old 09-03-2016, 09:29   #54
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Re: Which sealant for Lexan

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The Lexan in my old forehatch lasted 35 years until I replaced it due to crazing. US Plastics also sells the UV protected Lexan and I made Sunbrella covers for my deck hatches.
35 years - what brand of hatch?
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Old 09-03-2016, 09:49   #55
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Re: Which sealant for Lexan

Atkins & Hoyle | Boat & Marine Dinghy Davits, Hardtops and Arches

The hatch is a very heavy framed aluminum construction. It was easy to replace the crazed blue Lexan with a smoky grey Lexan and since I was bonding Sikaflex to aluminum and to Lexan, I had to use two different primers.
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Old 09-03-2016, 09:56   #56
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Re: Which sealant for Lexan

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Atkins & Hoyle | Boat & Marine Dinghy Davits, Hardtops and Arches

The hatch is a very heavy framed aluminum construction. It was easy to replace the crazed blue Lexan with a smoky grey Lexan and since I was bonding Sikaflex to aluminum and to Lexan, I had to use two different primers.
Not real surprising that it lasted 35 years really - it was acrylic.

From the Atkins & Hoyle website:

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Old 09-03-2016, 11:20   #57
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Re: Which sealant for Lexan

Ha! Rather funny. The thing is, people hear about Lexan being bulletproof etc. so they are programmed to think it is better. And for stopping bullets it may be. For hatches and boat windows, I believe Plexiglass is better, even though Lexan has that point loading advantage.

Now, here is the thing about Lexan with UV coating: the edges of the window, the ones you cut to make it fit, obviously don't have the coating. If those edges are exposed to daylight (even indirectly), then it can enter the material through that edge and the coatings reflect it back in everytime, so that it travels all through the material much like a laserbeam through an optic fiber, damaging the Lexan everywhere, leading to completely clouded windows.

So, if a cut (routed/rounded/bevelled) edge is exposed to daylight, it must be painted. It's better to frame it or embed it etc.

Plexiglass does not have this problem and it is also much more scratch resistant.
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Old 09-03-2016, 11:42   #58
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Re: Which sealant for Lexan

Once again, thanks so much for everyone's input.
Ken
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Old 09-03-2016, 12:04   #59
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Re: Which sealant for Lexan

Interesting point about the cut or beveled edge.

During installation I taped the hatch flange and the lens at the edge of the flat surface, leaving the beveled edge exposed. Then pressed the lens in place, added a spooge of sealer on top, and use an old credit card to smooth it around the perimeter.

After it began to set I removed the tape. The result has the appearance of a factory gasket of some sort. Before doing this I drew a crossection diagram of the idea and showed the skylight guy. He offered a slight change, which I did, and said good idea.
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Old 09-03-2016, 12:45   #60
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Re: Which sealant for Lexan

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Originally Posted by s/v Jedi View Post
Ha! Rather funny. The thing is, people hear about Lexan being bulletproof etc. so they are programmed to think it is better. And for stopping bullets it may be. For hatches and boat windows, I believe Plexiglass is better, even though Lexan has that point loading advantage.

Now, here is the thing about Lexan with UV coating: the edges of the window, the ones you cut to make it fit, obviously don't have the coating. If those edges are exposed to daylight (even indirectly), then it can enter the material through that edge and the coatings reflect it back in everytime, so that it travels all through the material much like a laserbeam through an optic fiber, damaging the Lexan everywhere, leading to completely clouded windows.

So, if a cut (routed/rounded/bevelled) edge is exposed to daylight, it must be painted. It's better to frame it or embed it etc.

Plexiglass does not have this problem and it is also much more scratch resistant.
Have you ever seen the curved plexi windows on a circa 49 Steel Craft. Checked all to hell. Granted it may have improved. I have used it for other applications in R&D but not for UV exposure just nasty chemicals. I have used Lexan for of all things 76 kennel pull up doors. Provided light and never had a 100+ dog run through it but did scratch.

I have no dog in the fight, no pun intended . All I can do is offer an opinion maybe based on experience?
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