Plexiglass replaced in hatch, came unglued. - Page 2 - SailNet Community
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post #11 of 22 Old 04-24-2018
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Re: Plexiglass replaced in hatch, came unglued.

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Originally Posted by SeaStar58 View Post
Yes 3/16" seems a bit light duty for a hatch that could be stepped on.
Although, the hatch lens looks well supported.

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post #12 of 22 Old 04-24-2018
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Re: Plexiglass replaced in hatch, came unglued.

I designed commercial and residential skylights for a couple of decades. The best/most common joint for a non-mechanical mounting like that would be structural glazing tape or VHB tape with Dow 795 to seal and adhere. There are more than a few posts on this site about it. One guy did a bang up job e'splaining the process. Better than mine. At any rate, keep a few things in mind when you do this.

1) Not all plastic glazings are equal. Lexan (polycarbonate) takes a blow better than Plexiglass (Acrylic) but it scratches easier. Impact modified acrylic is a good compromise.

2) Not all adhesive/sealants are equal. The glues used was probably not formulated for acrylic, or at least not for the application. Most, if not all, polyurethane selants will cause plasticizer migration in the plastic. It will craze and crack the glass and release from the surface.

3) The sealant is intended to be a live connection. The hull and the glazing will move due to wind, weather, heat, cold, impact and just for the fun of it. And not at the same time or the same distance, heck not even in the same direction. So the joint should be thick enough to stretch and return. A minimum joint is 1/4" but you can probably get away with 1/8 on a small hatch.

4) A proper sealant joint should only be attached on two sides. Pull a rubber band from the ends. Not grab the middle and pull. Same thing but not as much give so it tends to eventually rip.

5) A joint MUST be tooled to be effective. A non-tooled joint will not be warrantied. So, a squirt of alcohol (ON the SILICONE!) and run your finger over it to make it pretty also makes it pass muster.
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post #13 of 22 Old 04-24-2018
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Re: Plexiglass replaced in hatch, came unglued.

Wow, a use for actual silicone!
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post #14 of 22 Old 04-25-2018
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Re: Plexiglass replaced in hatch, came unglued.

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Wow, a use for actual silicone!
You have to choose wisely though and get those rated as adhesives not just sealants with very light bonding properties.

You also have to look at material compatibility. The Sikaflex 295 UV is formulated for Acrylics along with, per Dons info, the Dow 795.

Then comes proper surface preparation and application.
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post #15 of 22 Old 04-25-2018
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Re: Plexiglass replaced in hatch, came unglued.

I'm a sillycone hater but was forced to use 795 replacing port lenses on my boat with the Catalina DIrect Kit. This was for two large fixed ports with an aluminium surround and a gasket between the extrusion and the plexi. Still don't like the stuff but less of an aversion to 795. It's way easier to work with at least in applying to the rubberized sealing gasket around the window and frame. Didn't seem to skin surface cure as fast regular sillycone so wasn't pressed to get it together. Cleaned it up with plain paper towels just wiping the excess off with a bit of elbow grease. Masked the plexiglass before applying the 795 so it went mostly on the gasket, plexi and frame which minimized clean up. Used butyl to seal the frames to the cabin side.

Lexan may be bullet proof but I don't intend to go into battle any time soon. Lexan surface is softer than plexi so scratches easily but worse, it crazes much faster when exposed to UV, corrosive cleaners and environmental abuse. The hatch on the PO's boat has fairly closely spaced reinforcing so the unsupported sections of plexi are small and withstood use abuse and the environment for probably 30 years before being assaulted by the vindictive evil snatch block.

Last edited by roverhi; 04-25-2018 at 01:04 AM.
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post #16 of 22 Old 04-25-2018
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Re: Plexiglass replaced in hatch, came unglued.

One of my Lewmar hatches had it's handle adheased to it, and it fell off. The prior owner tried to glue it back and made a huge mess, and it was not long before I broke it off again. My solution was to ship the entire lid to Hatch Masters in CT. They did a great job replacing the lens with a new, through bolted handle. They have a long lead time though, so call ahead.
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Re: Plexiglass replaced in hatch, came unglued.

I'd suggest you call the 800# on the back of the tube. 3M has excellent customer service and that product has a 12-month guarantee. If nothing else, they'll probably replace it and may replace it with a better product.

Assuming it was genuine Plexiglass, I'm guessing that the plexi was not clean, so the initial bond did not form. Or the plexi warped slightly in the heat of the sun, breaking the initial bond. 3M will probably have a better idea.
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post #18 of 22 Old 04-26-2018
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Re: Plexiglass replaced in hatch, came unglued.

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Originally Posted by roverhi View Post

Lexan may be bullet proof but I don't intend to go into battle any time soon. Lexan surface is softer than plexi so scratches easily but worse, it crazes much faster when exposed to UV, corrosive cleaners and environmental abuse.
Bingo. Acrylic has every advantage over polycarbonate in boating applications, unless you expect to be shot at.
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post #19 of 22 Old 04-27-2018
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Re: Plexiglass replaced in hatch, came unglued.

"Acrylic has every advantage over polycarbonate in boating applications, unless you expect to be shot at."
Not quite. There are literally dozens of grades of polycarbonate, and acrylics, from several major sources. To make blanket comparisons is like saying "I don't want to use metal, the last metal faucet I had rotted out." Really? Plated plastic, high quality stainless, solid bronze, gold flashed nickel-steel....they're all "metal" but all very different.
The same thing goes with glazing plastics. The stuff on the shelf is just intended to be used for napkin holders and drink coasters. The full range in a catalog will include many degrees of UV and scratch resistance--at much higher prices, and higher again because a small store will require you to order in whole 4x8 sheets of them. Even in Lexan, you can buy Lexan MR10, which has a film bonded to one or both sides, and that film tremendously increases the UV and scratch resistance. In Plexi, there are oddities like "unshrunk type G" which used to be specified for underwater camera housings for some technical reason.

Some years ago my friend enlisted me to tear old the old portlights and put new ones in. I asked him if he really was going to just replace the old ones "same same" and he said sure, of course, they're Lexan they're incredibly strong. And since we were going to implode the old ones to remove their glued frames, and I was already leaning against the cabin side with an ordinary hammer in my hand. I just swung my arm out (BLAM!) and said "I don't think they're Lexan."
To me, the question is, when something falls apart and a spinnaker pole or other hefty "missile" shoots back into the glazing, will it penetrate? Or be stopped? If a guy up the mast drops a monkeywrench, will it penetrate? Or be stopped?
Acrylics can have a strength range of well over 10:1 comparing one grade to another. Lexan can be more than 100x more impact resistant than acrylics.
If you read about the damage boats took in "Fastnet, Force 10" and how many needed to rig storm windows, etc? Lexan doesn't begin to sound so bad. Polish it once a year, keep ammonia and petrochemicals off it, not so hard to keep it up.
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post #20 of 22 Old 04-27-2018
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Re: Plexiglass replaced in hatch, came unglued.

Quote:
Originally Posted by hellosailor View Post
"Acrylic has every advantage over polycarbonate in boating applications, unless you expect to be shot at."
Not quite. There are literally dozens of grades of polycarbonate, and acrylics, from several major sources. To make blanket comparisons is like saying "I don't want to use metal, the last metal faucet I had rotted out." Really? Plated plastic, high quality stainless, solid bronze, gold flashed nickel-steel....they're all "metal" but all very different.
The same thing goes with glazing plastics. The stuff on the shelf is just intended to be used for napkin holders and drink coasters. The full range in a catalog will include many degrees of UV and scratch resistance--at much higher prices, and higher again because a small store will require you to order in whole 4x8 sheets of them. Even in Lexan, you can buy Lexan MR10, which has a film bonded to one or both sides, and that film tremendously increases the UV and scratch resistance. In Plexi, there are oddities like "unshrunk type G" which used to be specified for underwater camera housings for some technical reason.

Some years ago my friend enlisted me to tear old the old portlights and put new ones in. I asked him if he really was going to just replace the old ones "same same" and he said sure, of course, they're Lexan they're incredibly strong. And since we were going to implode the old ones to remove their glued frames, and I was already leaning against the cabin side with an ordinary hammer in my hand. I just swung my arm out (BLAM!) and said "I don't think they're Lexan."
To me, the question is, when something falls apart and a spinnaker pole or other hefty "missile" shoots back into the glazing, will it penetrate? Or be stopped? If a guy up the mast drops a monkeywrench, will it penetrate? Or be stopped?
Acrylics can have a strength range of well over 10:1 comparing one grade to another. Lexan can be more than 100x more impact resistant than acrylics.
If you read about the damage boats took in "Fastnet, Force 10" and how many needed to rig storm windows, etc? Lexan doesn't begin to sound so bad. Polish it once a year, keep ammonia and petrochemicals off it, not so hard to keep it up.
Well put. Thanks.

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