Portholes Revisited

Discussion in 'Materials' started by Asleep Helmsman, Aug 6, 2021.

  1. Asleep Helmsman
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    Asleep Helmsman Senior Member

    Good Morning Guys,
    Still on this porthole thing. I've made good progress painting the boat while still in the water. Long story get back to you later.

    One question and one question only.
    Is there a material on the market that will act as both an adhesive, and a sealant for putting frameless Plexiglas over an epoxy coated FRP surface?

    I am trying to do this without mechanical fasteners every 2 1/2" around these windows. I know this is an old question, but a guy down at the marina claims they successfully use polyurethane windshield adhesive.

    Thanks
     
  2. Blueknarr
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    Blueknarr Senior Member

    There's lots of choices.
    Some depend on the portlight's dimensions and overlap with the hull.
    Automotive windshield adhesive should work if sufficient overlap.
     
  3. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    How much overlap would be sufficient?
     
  4. Asleep Helmsman
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    Asleep Helmsman Senior Member

    I was thing 1.125 inches?
     
  5. Asleep Helmsman
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    Asleep Helmsman Senior Member

    This came from 3M.


    Hello Joe,


    Thank you for contacting 3M.


    Unfortunately the 3M™ Fast Cure Auto Glass Urethane 08690 will not work to bond Plexiglas. Currently 3M Automotive Aftermarkets does not have a solution.


    Regards,
     
  6. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    Pictures, please.
     
  7. Rumars
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    Rumars Senior Member

    There are several options: VHB tape, Dow 795, GE Silpruf 2000, Life-Seal, Sika 295, etc. It's important to have sufficient thickness in the joint for expansion, and rigid enough Plexiglass for the span.
     
  8. Asleep Helmsman
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    Asleep Helmsman Senior Member

    VHB Tape it is.

    What do y'all think, 1 1/8" overlap with 3/4" or 1" tape to the inside of the opening?
    After it is attached go around the outside with a sealant caulk?

    I already have some of the non adhesive Total Boat Elastomeric Marine Sealant which they claim works on plexyglas as a sealant, not adhesive.

    I think this is what I'm going to try.

    Thanks Guys
     
    Last edited: Aug 7, 2021
  9. Barry
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    Barry Senior Member



    A pertinent video
     
  10. Rumars
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    Rumars Senior Member

    You need space on the outside of the tape to shoot caulking into. Does it mount into a recess or a frame?

     
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  11. Asleep Helmsman
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    Asleep Helmsman Senior Member

  12. Asleep Helmsman
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    Asleep Helmsman Senior Member

    I'm a gig guy. I use them for everything. In Andy's video he had the recessed area to align the acrylic sheet, and since he used black caulking it would be a little forging of misalignment.
    In this project the portholes will be outside the cabin. another condition to overcome is that the two large port holes in the Solon area are in line. This will require more align accuracy.
    I'll take some photos.
     
  13. Rumars
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    Rumars Senior Member

    Dow 795 is a structural adhesive, it keeps glazing on skyscrapers, not your bathroom silicone. The way to insure the portlights stay leakfree is to have enough gap between the acrylic and the cabin side so that the sealant can compensate for movement, make sure the tape is thick enough.
    Paint the area over the tape and sealant black, it protects it from the UV, can be done on the outside.
     
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  14. Asleep Helmsman
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    Asleep Helmsman Senior Member

    The tape is 45/1000 ths
     

  15. Rumars
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    Rumars Senior Member

    A little tight to be squeezing sealant in afterwards, at least for me. The gap depends on port size and acryl thickness, you can look up how much it moves per degree of temperature increase, and match it to the sealants characteristics.
     
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