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Old 02-03-2016, 15:40   #31
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Re: Which sealant for Lexan

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Originally Posted by deblen View Post

For holding AND sealing-use Sika,4200,or your favourite compound-except silicone.
Silicone is only useful as a gasket between two mechanically clamped(by bolts/screws,etc) items & has very few if any uses on a boat. Len
Silicone is best not used on a boat - except for glazing - hatches and ports. Dow 795 is not normal silicone but a structural adhesive. Industrially used for adhering glass on highrise buildings without fasteners. It is used by many hatch/port manufacturers as well as Select Plastics, the largest hatch refurbisher in the world. Other good choices are GE Silpruf 2000 and Sika 295UV which needs the proper primer.

On Plexiglas vs Lexan - all major hatch manufacturers use Plexiglas with one exception. The exception is Bomar on some models. The Bomar hatches using Lexan have crossbars under the Lexan as without it the Lexan would flex if stepped on, breaking the seal.
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Old 04-03-2016, 23:53   #32
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Re: Which sealant for Lexan

Unless you are going to protect that Lexan from the sun & uv, I would strongly suggest you consider acrylic. A year in the sun and Lexan is weaker than acrylic. If you have fasteners, use butyl tape. If not, use Dow 795. Run your question by hatch masters.


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Old 05-03-2016, 01:53   #33
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Re: Which sealant for Lexan

Some info on the various Sika 29xx series.

https://www.sika.com/en/solutions_pr...ts-yachts.html
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Old 05-03-2016, 04:56   #34
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Re: Which sealant for Lexan

Acrylic is a harder material than polycarbonate and therefor more scratch resistant. Use Dow 795 adhesive caulk.
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Old 05-03-2016, 17:34   #35
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Re: Which sealant for Lexan

"Lexan" and "Plexiglass" are meaningless terms. That's like saying "Wood" or "Metal", there are all different kinds. Aside from the many grades of each of them, there are different products from competitors.


The windows on passenger trains have been required under federal law to be polycarbonate, because it is available as the most bullet-resistant material to do the job. Yes, hunters take "fun" shot at cross-country trains, so for many years before 9/11, they were required to be bullet resistant. There's no such thing as "bullet proof" unless you specify the bullet, because someone always makes a bigger bullet. And a stronger glazing material.


If polycarbonates like Lexan (but not every grade of Lexan, and you can bet the stuff in the corner store with no grade marked on it is simply CHEAP STUFF) can resist UV and bullets better than any acrylic...they won't melt in the sun on your hatches. That's if you look up the properties on the manufacturer's web site, and order the right grade of material.


And 3M will gladly tell anyone who can figure out how to call their toll-free number, 3M's "4000" product is the right one for Lexan. Not 5200, not 4200, but 4000. Whether GE approves of it or not, 3M guarantees it works. GE would rather not endorse their competition. (I think GE sold off their polycarbonates and other materials to some German? firm a decade ago though.)
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Old 05-03-2016, 18:00   #36
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Re: Which sealant for Lexan

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"Lexan" and "Plexiglass" are meaningless terms...

If polycarbonates like Lexan (but not every grade of Lexan, and you can bet the stuff in the corner store with no grade marked on it is simply CHEAP STUFF) can resist UV and bullets better than any acrylic...they won't melt in the sun on your hatches. That's if you look up the properties on the manufacturer's web site, and order the right grade of material.
I believe this to be incorrect advice. I'm not trying to argue or get into a tinkling contest, just making a couple of points. And my info comes from an expert.

1) Both terms are trademarked products. One is polycarbonate, the other acrylic.

2) Lexan is NOT the product of choice on a boat. Above I suggested that the OP contact Hatchmasters about this. It was perfect advice. Tony has been a regular contributor here, and NO ONE knows his stuff on poly vs. acrylic better than Tony. PLEASE READ HIS BLOG ON POLYCARBONATE VS. ACRYLIC. It's the advice you want.

https://hatchmasters.com/acrylic-vs-polycarbonate/
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Old 05-03-2016, 18:14   #37
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Re: Which sealant for Lexan

GE sold Plastics to Sabic.

https://en.m.wikipedia.org/wiki/SABIC
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Old 05-03-2016, 19:50   #38
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Re: Which sealant for Lexan

The OP's question was which adhesive to use with Lexan, not whether to use Lexan versus acrylic. I'm not debating the suitability of either material, or the priorities that lead to choosing one over the other. My hazy memory is that generally, polycarbonate will have 10x-100x the impact resistance of acrylic, no matter how good an acrylic you spec. So if your boat was built with frames of 1/4" glazing, and you want to make Real Damn Sure a spinnaker pole can't smash one in...there may be no contest between the materials.
There are applications, like protective headgear, train windows, and even spacesuit helmets, where acrylics simply are not used, but polycarbonates are. Same thing for the lenses in protective eyegear. When the criteria is "strength per thickness" polycarbonates win every time. I've got a polycarbonate storm window that's been up and exposed to sunlight and weekly washing for two years now--and it still looks like glass.
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Old 05-03-2016, 20:24   #39
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Re: Which sealant for Lexan

This thread is hurting my head.

Sabic makes lexan, lexan is polycarbonate and lexan can be ordered with UV blocking properties, so lasts as long or longer than acrylic.

Gord has the adhesive/sealant right.

My entire boat is windows. All Lexan
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Old 05-03-2016, 21:09   #40
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Re: Which sealant for Lexan

I had 3/8 inch smoked bronze Lexan cut for my hatches, with the edges beveled to fit flush on the edge in the Bomar hatches.

A company that builds skylights did them for me from leftover cutoffs. Only $80 total for two and they gave me a partial tube of sealant for the job but can't remember the brand. The originals were thinner and heavily crazed, though 30+ years old.

I asked about crazing and the guy just smiled and said I wouldn't have to worry about that. Must have been true as now almost six years later they still look like new.

One canvas cover has a square hole in the middle where a solar vent once was installed. That section has never been covered to protect it. Will look tomorrow to see if there is any UV damage, but haven't noticed any to date.

I think there is available some high quality Lexan out there.
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Old 06-03-2016, 13:15   #41
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Re: Which sealant for Lexan

OK, so the OP has chosen Lexan. Poor choice. Should we let him go down that road, or should we let him have to replace the Lexan in just a couple of years?

Did any of you bother to read Tony from Hatchmaster's blog about this? Didn't think so.

1) Lexan IS available with UV blocking, but generally only up to 1/4".

2) Lexan is so flexible that an impact with a pole, or just simply stepping on a Lexan hatch will break the seal. Or worse, it's so flexible that you could go right through. Great. That's what I want, a hatch that I can't even step on.

3) Tony recommends Sikaflex 295UV or Dow 795 for use with Lexan. Since he actually DOES the work for the CG and USN, I kind of trust his judgement...

P.S. You can't "see" the UV damage to Lexan - it weakens it structurally.
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Old 06-03-2016, 14:24   #42
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Re: Which sealant for Lexan

"1) Lexan IS available with UV blocking, but generally only up to 1/4". "
Funny, the first Google hit without trying found Lexan ML10, UV-resistant, 1/2" thick. Then there are all the other brands. Architects use this stuff for walkways, skylights, and all kinds of exterior glazing, and somehow, they prefer to use it. And don't have a UV problem with it.


Stainless steel, aluminum, bronze, and even glass will all either deform or break under the load of one crew stepping on them. No different from Lexan, you just have to specify the right structural grade for the opening you are covering.


I'm sure Tony has his reasons, but then again, perhaps that unobjectively also makes his business different from others, and superior to them. Or, it could just be one of several solutions, and just a selling point. If the USCG specifies acrylic and NASA specifies Lexan....could they both be right?
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Old 06-03-2016, 14:32   #43
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Re: Which sealant for Lexan

Ken said port lights not large areas. I would only be concerned with scratching maybe from salt? His question was about sealant not the pros and cons of Lexan. It is a good product and at 1/4 inch is bullet proof. Those that say it is breakable are blowing smoke.
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Old 06-03-2016, 14:42   #44
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Re: Which sealant for Lexan

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Originally Posted by hellosailor View Post
"1) Lexan IS available with UV blocking, but generally only up to 1/4". "
Funny, the first Google hit without trying found Lexan ML10, UV-resistant, 1/2" thick. Then there are all the other brands. Architects use this stuff for walkways, skylights, and all kinds of exterior glazing, and somehow, they prefer to use it. And don't have a UV problem with it.


Stainless steel, aluminum, bronze, and even glass will all either deform or break under the load of one crew stepping on them. No different from Lexan, you just have to specify the right structural grade for the opening you are covering.


I'm sure Tony has his reasons, but then again, perhaps that unobjectively also makes his business different from others, and superior to them. Or, it could just be one of several solutions, and just a selling point. If the USCG specifies acrylic and NASA specifies Lexan....could they both be right?
UV resistant Lexan is available in thicknesses greater than 1/4", but most often only in full sheets as I understand.

Tony isn't the only one to think acrylic is a better choice than polycarbonate. Every major hatch manufacturer in the world uses acrylic, with the exception of a few models from Bomar. Because it has less issues and lasts longer.
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Old 06-03-2016, 16:12   #45
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Re: Which sealant for Lexan

If you go Lexan, you really should get the MR10 version which has the MarGuard coating (abresion + UV resistant)

p.s. You can also use Makrolon which is the same polycarbonate. They have the required coatings as well.

Dow Corning 795 also has a longer working time so you have a chance to get it right
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