Click for Stats Click for Walker Click for JetForums Click for Burger Click for United

Best Sealant for Leaking Windshield

Discussion in 'Technical Discussion' started by KevinMC, Dec 19, 2017.

You need to be registered and signed in to view this content.
  1. KevinMC

    KevinMC New Member

    Joined:
    Dec 30, 2009
    Messages:
    4
    Location:
    Kent Island, Md
    Hello Captains,
    I've been a member of this form for quite a while and don't post very often. I read most of the new posts and learn from the wealth of experience present here. Hoping someone has had some experience with the issue below.

    A couple of years ago, over the winter, my 1994 boat (35' Luhrs SF) developed a crack in the windshield requiring replacement. It was replaced with an equivalent plexiglass material, but instead of a single piece, was split into a port/stbd window with a small center piece. I've included pictures of the open window frame and the newly installed plexiglass.

    Initially the vendor used some sort of roofing caulk, which worked fine until the heat of the summer (Maryland) caused the expansion/contraction of the plexiglass, which caused leaks from the top of the window inside the boat (not from the center). After several iterations of removing and re caulking, with the same results, last spring the vendor went to a new caulking product SikaFlex 295UV. This product worked for a while, and we thought we had the problem solved.

    After a full season of running, we recently saw the reappearance of leaks, although much less water than before. I'm positive that the leak is coming from the windshield because I placed shrink-wrap tape over all seams for the window, and there are no more leaks.

    I have been reading multiple internet articles that seem to recommend the Dow 795 sealant as the best for this application. It is my understanding that this sealant is used to affix the glass panels to skyscraper buildings (handling the expansion/contraction), and is compatible with the plexiglass material.

    I am planning to have the windshield removed and re-caulked this spring, and want to ensure that the best caulking material is used to hopefully resolve this issue. It is amazing that the factory windshield that
    was replaced (23 years old), never leaked. Unfortunately Luhrs is out of business, so I'm unable to ask them for the specific sealant that they used.

    Thank you in advance for your comments and suggestions! Kevin

    WINDSHIELD-IMG1-small_2345.jpg WINDSHIELD-IMG2-Small_2349.jpg
  2. Bamboo

    Bamboo Senior Member

    Joined:
    Dec 19, 2008
    Messages:
    931
    Location:
    Palm Beach, FL
    Bostik 70-03A is what you need. Non glass scratches, you'd be better off with glass IMPO.
  3. Bill106

    Bill106 Senior Member

    Joined:
    Jan 9, 2010
    Messages:
    368
    Location:
    Beaufort NC
    We've also had good luck with Boatlife Lifeseal when rebedding acrylic and glass in hatches and cabin windows.
  4. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    993
    Location:
    Dana Point, Ca
    The Dow system is probably the most cost effective solution. You have to prep/paint the window with a primer where it will come in touch with the sealant. The bond between the glass and the sealant should be stronger than the glass, you can make a test piece and try to break it to verify the effectiveness of the primer/sealant bond. There may also be another Dow sealant product that is used to trim out the finished installation, that is, the seal between the edge of the glass and the gap between the adjacent glass piece or exposed edge. This sealant should have the appropriate UV characteristics for long life. More expensive systems are available that require a special ceramic coating (called a frit) on the inside of the glass and uses special sealants. Sika has their own system as well.

    A few things to keep in mind - the glass has to be strong enough, have the correct edge gap when installed (for expansion)and the correct thickness for it's size. And the Window mullions that support the glass should be structurally sound to eliminate unnecessary flexing of the glass plate once in place. Also, the glass should be tempered or laminated safety glass.
  5. Prospective

    Prospective Member

    Joined:
    Sep 27, 2016
    Messages:
    84
    Location:
    New England
    I strongly recommend GE SSG4000 Ultraglaze structural glazing sealant. I have used it to reglaze portlights on bomar hatches and am using it to reglaze the side windows on my Ocean. What I've done so far has held up very well, no leaks, remains black and flexible. It is flexible, easy to work with, and very strong. And this is exactly the purpose of the product, structural glazing of windows. Don't use another multi-purpose product. That Sika stuff is a nightmare to work with and stupid expensive. Used it with a buddy on his sailboat. Never again. GE stuff is way better. It is 2 part and a pain in the ass to get right. So make sure you sand and clean the entire surface to get rid of it because nothing sticks to it including it's self. Here it is on Amazon. Cheap too and great reviews, mostly all by boaters. https://www.amazon.com/GE-SSG4000-U...5426&sr=8-1-fkmr0&keywords=ge+4000+ultraglaze
  6. Bamboo

    Bamboo Senior Member

    Joined:
    Dec 19, 2008
    Messages:
    931
    Location:
    Palm Beach, FL
    The best two yacht glass companies here in Palm Beach both use the Bostik; on vessels from 35 feet to 335 feet. Experience keeps a dear school as my father used to say. Some of the other suggestions may make you happy; YMMV.
  7. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    993
    Location:
    Dana Point, Ca
    I would be interested to know between Bostick, GE and Dow who makes their sealant products? Are they all developed and made in house or is their a plant that produces for either of them and others? Just curious, as all three are large companies and probably chase the global sky scraper business.
  8. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    9,932
    Location:
    Fort Lauderdale
    I too use the Boatlife lifeseal with very good results. But quite frankly the OP needs a glass windshield and I feel the brow of the Flybridge and it's movement, the angle of the plexiglass and it being black when it gets hot it starts bending and warping and such.
  9. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    5,291
    Location:
    Jax FL
    It was replaced with an equivalent plexiglass material, but instead of a single piece, was split into a port/stbd window with a small center piece.

    Probably the factory recognized a twisting problem and used one piece to hold the center edges down.
    Maybe had been a good experiment if you tried the white tape at different places.
    I bet the center. Also I bet the original crack near the center.

    Have you considered the path of hardened fishing boats? Fiberglass in the whole front window?
  10. KevinMC

    KevinMC New Member

    Joined:
    Dec 30, 2009
    Messages:
    4
    Location:
    Kent Island, Md
    Wow - Thanks for all of your responses - I was thinking I had only two choices and it looks like I have many more options to choose from.
    I will investigate all the products mentioned and will also consider replacing the entire windshield with a single pane of glass.

    Capt J - You are correct that the initial plexiglass that was installed did warp in the summer heat. The vendor removed and replaced with a thicker
    size of plexiglass (don't recall the thickness sizes right now)and then warping was no longer a problem.

    Rcrapps - Interesting point about the twisting - one point to be made the windshield also has countersunk screws along the perimeter holding it down in addition to the sealant (hard to see in the pictures). This was how the factory did it. The original crack was in the center of the pane opening on the starboard side. We can see the leaks (thru the glass)coming from the top seal, dripping down the interior of the pane, not near the split.
    Yes, I also I thought about fiber-glassing the whole thing, but we like the natural light that it provides and prevents the SF "cave" feeling when at anchor or in port.

    Again thanks to all for your thoughtful suggestions!
    Kevin
  11. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    9,932
    Location:
    Fort Lauderdale
    Your going to need to go to glass. Plexiglass no matter how thick, doesn't have the dimensional stability in the heat and will still warp and move no matter what the thickness as well as overheat and release the sealant. You could try another sealant such as some of the ones mentioned, but I think the summer heat is going to cause the plexiglass to release most all of them.

Share This Page