Plexiglass replaced in hatch, came unglued. - SailNet Community
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post #1 of 22 Old 04-23-2018 Thread Starter
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Plexiglass replaced in hatch, came unglued.

Dropped a snap shackle on the hatch and put a hole in the Plexiglass, whoops. So I just replaced it using the same 3/16" tinted Acrylic, custom cut for $63. I used 3M 4000UV to adhere the Plexiglass to the aluminum frame, but about a week later a lot of the glue UNadhered.
This is a Cal 39, capable of heavy off-shore cruising, so I'd like to trust the fix.

Any recommendations on products to fix the glass to the frame that will last 30 years?

Pic 1: I liked the old glue a lot. It lasted for at least 5 years since before I bought the boat, yet was fairly easy to pry off and clean. It was a black, rubbery feel, but I'm not sure what product it is. I cleaned it completely using a soft dremel, scrapers and acetone.
Pic 2: I then squeezed exactly 2 tubes of 3M 4000UV to replace the old glue, wiped the excess and pressed the bubbles out until tacky.
Pic 3: You can see there's no bubbles with full glue coverage the next day after drying. Should work, right?
Pic 4: I don't like how quickly the 4000UV tacked up, making it tougher to smooth out the bead, but that's cosmetic only.

2 weeks later, about 50% of the Plexiglass had loosened up from the Plexiglass (not the aluminum), allowing water to leak into the V-berth. You can press down on the glass and see where the glue is sticking and where it's not. Maybe use a different glue? Or did I not prepare the Plexiglass correctly? I just peeled off the paper and stuck it on the glue.

Thanks all!
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post #2 of 22 Old 04-23-2018
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Re: Plexiglass replaced in hatch, came unglued.

Most seem to recommend Dow 795 including these guys who rebuild marine hatches.
https://hatchmasters.com/product/dow-corning-795/

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post #3 of 22 Old 04-23-2018
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Re: Plexiglass replaced in hatch, came unglued.

The old was probably butyl.
1st guess is either prep or application problem with the new.
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post #4 of 22 Old 04-23-2018
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Re: Plexiglass replaced in hatch, came unglued.

There may be a primer for the plexiglass side especially when its not clamped into place with a frame and the sealant also has to serve as the adhesive to lock it down.

The adhesive sealant specifically for acrylic ports and hatches that I am aware of is Sikaflex 295 UV which I believe is a Polyurethane rather than a Silane Modified Polymer:

https://www.westmarine.com/buy/sika-...lk--P012586731

Last edited by SeaStar58; 04-23-2018 at 08:38 PM.
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post #5 of 22 Old 04-23-2018
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Re: Plexiglass replaced in hatch, came unglued.

Whoa. You "Dropped a snap shackle (1 pound or so?) on the hatch and put a hole in the Plexiglass"? on a boat you consider "capable of heavy off-shore cruising", and you replaced it with the same strength acrylic? When I broke one of ours by dropping the dinghy (250 pounds) on it, I moved up to 3/8th inch to insure there would never be a repeat of that experience, especially offshore. When the time comes to replace others, I shall do the same.
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post #6 of 22 Old 04-23-2018
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Re: Plexiglass replaced in hatch, came unglued.

How much flange is there that overlaps with the plexiglas? When I redid my windows I used 3M VHB tape to hold them and then sealed with Dow 795. No leaks so far and I don't think that I could pull the window off the boat with both hands and a crowbar. If you have room to put the tape (i used 1/2") this seems pretty bombproof.
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post #7 of 22 Old 04-24-2018
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Re: Plexiglass replaced in hatch, came unglued.

Quote:
Originally Posted by capta View Post
Whoa. You "Dropped a snap shackle (1 pound or so?) on the hatch and put a hole in the Plexiglass"? on a boat you consider "capable of heavy off-shore cruising", and you replaced it with the same strength acrylic? When I broke one of ours by dropping the dinghy (250 pounds) on it, I moved up to 3/8th inch to insure there would never be a repeat of that experience, especially offshore. When the time comes to replace others, I shall do the same.
Yes 3/16" seems a bit light duty for a hatch that could be stepped on.
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post #8 of 22 Old 04-24-2018
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Re: Plexiglass replaced in hatch, came unglued.

Quote:
Originally Posted by capta View Post
Whoa. You "Dropped a snap shackle (1 pound or so?) on the hatch and put a hole in the Plexiglass"? on a boat you consider "capable of heavy off-shore cruising", and you replaced it with the same strength acrylic? When I broke one of ours by dropping the dinghy (250 pounds) on it, I moved up to 3/8th inch to insure there would never be a repeat of that experience, especially offshore. When the time comes to replace others, I shall do the same.
Well, he COULD have dropped from the top of the mast..........
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Re: Plexiglass replaced in hatch, came unglued.

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Originally Posted by lillia28 View Post
Well, he COULD have dropped from the top of the mast..........
Which is what I assumed!

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post #10 of 22 Old 04-24-2018
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Re: Plexiglass replaced in hatch, came unglued.

Which is what I assumed![/QUOTE]

Then I'm behind the curve, as I did not originally think that.
Lexan for the lens then?
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