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Old 30-03-2009, 06:53   #1
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Lexan Bonding

I am replacing the lens on my forehatch with 1/2" Lexan. I am researching which adhesive/sealants are best for my project.

I am bonding the Lexan to aluminum and don't want to destroy the Lexan.

I have contacted DAP and 3M, so are 5200 is in the lead, but I can't find out how it reacts to Lexan polycarbonate.

Any experiences to relate?

George DuBose
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Old 30-03-2009, 07:01   #2
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Originally Posted by George DuBose View Post
I am replacing the lens on my forehatch with 1/2" Lexan. I am researching which adhesive/sealants are best for my project.

I am bonding the Lexan to aluminum and don't want to destroy the Lexan.

I have contacted DAP and 3M, so are 5200 is in the lead, but I can't find out how it reacts to Lexan polycarbonate.

Any experiences to relate?

George DuBose
S/V Skylark Pearson 36-1
George,

I would highly recommend Acrylic over polycarbonate for that application. That hatch, and most every brand on the market, came with Acrylic from the factory. Acrylic is more scratch & UV resistant and it will be very, very difficult to find UV/scratch resistant Lexan/polycarb in either 3/8" or 1/2" thick.

As for sealant Dow 795 is the most widely used sealant for this type of application. Alternatives are Sika Flex 295 UV with the primer & GE SG-4000.

You should really consider sending your hatch to Select Plastics (world largest hatch repair facility) and having it done right and with the industry preferred materials.
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Old 30-03-2009, 07:32   #3
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I would agree with Maine Sail. Cast acrylic is what the best hatches are made from. This is not the case for the really cheap (none are really cheap). You are not trying to chemically bond the acrylic to the frame. You are making a flexible and compressible seal. Having it both UV and marine resistent would include the list above. This would make a good seal and allow you to redo it later on. With acrylic and god sealant you will be able to redo the seal years later.

My ports are all cast acrylic and are 17 years old and looking great. The frames have been remounted a few times. The naural expansion and contaction eventually will force that over a long enough period of time.
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Old 30-03-2009, 08:02   #4
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My Lewmar acrylic hatchs that face the sun are crazed at 6 years old. Side facing ports are fine. I'm going with Makrolon if I can get it thick enough. Have not started looking yet.
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Old 30-03-2009, 08:54   #5
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If you do go with Lexan don't use 3M 5200, apparently it reacts with the lexan and thats not good. I've read that either 3M Marine Silicone or 3M 4000UV are the recommended 3m sealants. I personally tend to avoid silicone myself for several reasons, especial because of its weak bond.
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Old 30-03-2009, 09:28   #6
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You may also want to look at 3M VHB Tape. They were designed to attach glazing to metal mullions in building windows. Then waterproof and seal with the goop of your choice.
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Old 30-03-2009, 10:25   #7
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Originally Posted by Pblais View Post
I would agree with Maine Sail. Cast acrylic is what the best hatches are made from. This is not the case for the really cheap (none are really cheap). You are not trying to chemically bond the acrylic to the frame. You are making a flexible and compressible seal. Having it both UV and marine resistent would include the list above. This would make a good seal and allow you to redo it later on. With acrylic and god sealant you will be able to redo the seal years later.

My ports are all cast acrylic and are 17 years old and looking great. The frames have been remounted a few times. The naural expansion and contaction eventually will force that over a long enough period of time.
My cast Acrylic hatch glass lasted 30 years!!!!!!!!!!! Just replaced it a few weeks ago with Cyro's Acrylite GP. If your glass is crazing at 6 years it is more likely due to the quality of the original Acrylic or care and maintenance. There are certain products eg: Windex, that will destroy Acrylic in very short order.
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Old 30-03-2009, 10:57   #8
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George,
I would use a good silicone glazing caulk like Dow Corning« 999-A Silicone Building & Glazing Sealant

I would also use a good primer (THIS IS A MUST!) I've useed Dow 1200 red (the red will fade out in a week or so but in the meantime you are sure that you are getting a good coat on both the frame and lexan - clean and rough up both where primer and sealant will be applied). Without the primer the caulk WILL NOT stick to the aluminum. See the following site for more details:
Dow Corning 1200 Prime Coat - Dow Corning - SURFACE PREPARATION

Good luck, Bill A.
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Old 30-03-2009, 11:00   #9
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Well, Lewmar was the manufacture, so I would guess it was quality stuff. And I'm very aware that cleaners can be the problem. I did have the boat on the hard here in Mexico. (read intense sun/heat) I also have kept hatch covers on both of the ones in question. Please note that the other ports not facing the sun are fine. Nonetheless, Makrolon is a superior product IMO. Not vulnerable to wrong maintenance or weather. A least check it out. They are building solar panels with it.
Makrolon® - Product description*-*Plastics TechCenter

My dodger windows are made out of it.
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Old 30-03-2009, 11:56   #10
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Maine Sail,

I hope I don't come off as contrary. Your 30 year old hatch looking like new is something that nobody can argue with.

My boat is a 1973 Islander. There was a guy in my former marina who used to work for Islander. He told me that in 1973 Islander had a good resin formula. But that it was changed in 1974 and they blistered like clockwork. Islander fixed the formula, but they had to.

My point is, I'm wondering if this isn't a case of older being better. There are a lot of crazed hatches out there as this forum will attest to. Whatever you have done right, well,... I feel a little stupid.

One of the things I love about this forum is that I often hear about the "latest & greatest" here. I also get to learn old tricks from others.

If a product can stand improper maintenance and neglect better than another, I need it. I'm somewhere between a "low maintenance" & "no maintenance" guy.

I have Makrolon front windows sewn into my dodger, right next to brand new Strataglass for the side curtains (so I can roll them up for storage). There is a graininess in the new Strataglass that I never woiuld have noticed if it weren't for the Makrolon. It holds up to weather and resists scratching better, it's sewable (when it's thin) and non breakable. It's what all the water bottles are made out of. Unfortunatly, they don't degrade when we need them to.

It's a Bayer product. They should hire me. Sorry to souind like they already did. And for hijacking the thread.
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Old 30-03-2009, 12:22   #11
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How did a caulking gun end up on the same peg a back saw?
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Old 30-03-2009, 13:00   #12
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Old 30-03-2009, 13:23   #13
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Old 30-03-2009, 13:47   #14
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Did you guys delete a post??

Did you guys delete a post of mine or did I hit preview instead of send????
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Old 30-03-2009, 14:40   #15
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You don't have to

Guy you don't need to take my word for this. Here are some quotes from Tony D'andrea who is the Acrylic & Polycarb guru in the marine industry. He is the Nigel Calder of portlights and hatches and owns the largest hatch warranty & repair facility in the world..



Tony on Acrylic vs. Polycarbonate:



"Consider the Following:


  • All major hatch, portlight and window manufacturers use Acrylic in offshore / bluewater marine products.
  • Acrylic is more scratch resistant than standard (9034) polycarbonate.
  • Acrylic is significantly more durable when exposed to Ultra Violet radiation (sunlight).
  • Acrylic is less expensive than Polycarbonate.

Don't misunderstand my preference for acrylic. I buy, use and sell a significant amount of both products and each has its application. In my humble opinion Acrylic is more durable, versatile and cost effective in the hands of a skilled craftsman than polycarbonate.

Additional considerations may include polycarbonate with UV and scratch resistant coatings. While these products are heavily promoted by several manufacturers and carry 5, 10 even 15 year warranties the following information has been reported in "real life"applications:
  • Polycarbonate is impact resistant. When its new it is almost impossible to break.
  • Small quantities (less than a 4 by 8) in gauges over 1/8th inch are difficult to to find in the uv/scratch resistant grades.
  • Colors are limited. Only two standards (gray and bronze). Try and find anything thicker than 1/4 in UV/ scratch resistant!
  • Polycarbonate foreshortens when subject to static or dynamic loads. What this means is if you replace your hatch lens with polycarb, seal it and then step on it the ductile material will deflect (bow) in the center. One of two things may happen. 1st you will surely break the watertight seal, 2nd you may end up with a leg in your galley.
  • As for the warranty: The original owner is warranted against failure subject to the material being submitted to the distributor for evaluation with the original invoice subject to actual replacement cost at the time of purchase. I guess this means they sell you a new square of material and apply the old payment to the new cost. How about the labor to fabricate the part, install it and sealant? Why take the chance?
Polycarbonate is a great material, The US Air force uses it for fighter canopies! I sell Polycarb to the USCG and US Navy. Remember they don't mind using it because we are paying to replace it every three years.
Both Acrylic and Polycarbonate have specific uses and installation requirements.

Cast Acrylic (of a specific thickness) is in accordance with CE and ABYC guidelines, and installed on virtually all of the big blue water sail boats produced on both sides of the pond. Polycarbonate is commonly used as a replacement due to its ease of fabrication and incredible initial strength. The USCG and USN require Polycarbonate on their vessels but they also have a PM cycle of 36 to 42 months for change out. My Tax dollars at work...

Due to its ductility Polycarbonate it is more challenging to install. I have seen Sika Flex 295UV with primer and Dow 795 both mentioned. I use and recommend both. Dont go over 4 ft continuous length with a fixed portlight. Remember the coefficiant of thermal expansion for Acrylic and Polycarbonate is in the neiborhood of .000039 per inch per degree F. That means an 8ft plastic port will expand and contract up to 1/2 of an inch from the coldest day in Feb to the hottest day in summer. WOW!! Compartmentalize the job. It will be easier to install and less prone to leaks.

Never ever bolt a plastic portlight in place. Screws are fine to hold a lens till the adhesive cures. Take them out asap and fill the holes with the afformentioned products. Both of these products are rated at 700 + percent elongation before tear.
Strong flexible and UV resistant.

Been to a boat show lately? Seen any screws? Glass is good so long as your boat does not twist or torque. Show me a fiberglass boat that does not twist and I will show you a cocktail barge tied to the dock.
"

Tony on Sealants:

"I hear the question as to which sealant to use when bonding Acrylic, or Polycarbonate to aluminum, stainless or FRP over and over and over.....
Well here goes... The only three adhesives I would consider using are Sika Flex 295 UV with the primer, GE SG-4000, and Dow 795. Using the correct adhesive is only 1/2 the battle. Do not apply the sealants below 50 degrees F. The temperature must maintain at least 50F during the entire 21 day cure cycle. Cut this corner and your finished before you start. Preparation of the bond area is also very/ very important. DO NOT TOUCH THE BOND AREA WITH YOUR BARE HANDS! Contamination from the dirt and skin oils will make a solid cure impossible. You may clean the FRP and metal with acetone to prep the area but if you touch the Lexan or Plexi with harsh solvents you will ruin the portlight. A 50/50 mix of isopropal alcohol and distilled water will work well to clean the plastic if needed. Remember that clean enough is not clean enough."
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