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Old 18-08-2015, 12:35   #16
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

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Took care of the front Lexan window replacements, but now have a leak in the head area which has GLASS windows. Windows are floating in black sealant, recessed in a gelcoat black fiberglass frame. The Seka product I used to do the Lexan is not recommended for glass. Someone suggested a GE product but no number. Looks like SCS2000 SilPruf would be recommended, and I have seen that recommended for Lexan as well. (Should have probably purchased this for both the Lexan and glass windows, but too late now.)

Anyone have a recommendation. I need to remove two glass panels in the single recessed area, clean it all up, and rebed.

Oh, and the manufacturer originally used 1/4 inch by 1 inch thick, high-density double-sided tape to hold the window in place while the sealant set. I have not been able to find any that had tenacity similar to what was removed. Most are very "squishy". Anyone have a source? 3M doesn't make it, except for very thin. And needs to be black.

THANKS
Make sure before you rebed it that it sits flat. If you preload the window with a twist or bend the sealant will likely fail. Elastomers fail by peeling first and rarely shear or tension.

If you make a jig, perhaps with a suction cup or standoffs to ensure it doesn't slip, you'll improve the seal. The application of sealant is a goldilocks problem. Too little is often as bad as too much. You might want to run a trial to work out how to right size the nozzle.

Others have given sealant advice so I wont comment except to say make sure you consider the difference in thermal expansion between your window and the surround.

For example don't use a rigid setting elastomer in a poly or glass window in an aluminum frame. The thermal expansion will quickly degrade the seal.

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Old 18-08-2015, 12:46   #17
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

3M Windo-Weld 08609 with 3M Single Step Primer 08682
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Old 18-08-2015, 16:55   #18
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

Just to catch up. Yes, I used SekaFlex 295 UV on the front Lexan window replacement, after activator and primer. That product doesn't work on glass, and the one they have for glass is specified professional only, and only comes in the large sausage tubes.

I am now putting in a glass window. The Owens Corning product looks like it will work, as will GE SCS2000 SilPruf. I need to find the two-sided, 1/4 in thick tape though as that is needed to hold it in place until the sealant sets up. The window is in a vertical position on the outside of the hull. Here is a picture. It is actually two glass pieces behind the chain plate. The window frame is recessed, and molded into the hull (actually is the hull).
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Old 18-08-2015, 17:17   #19
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

That reminds me....some time ago there was this stuff:

https://sugru.com/about

Here's the CF mention (sorry about the cobwebs):

Trimaran - Especially Searunner - Owners

Has anybody had experience with it?
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Old 19-08-2015, 20:02   #20
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

Thought Maine Sail might chime in here since he has posted some excellent references in the past on installing/bonding/sealing lights and hatches. Here is a link from 2009....wish I had found it before I bedded my Lexan with Sika295uv a few years ago. Didn't last a year. I've now rebedded with Dow 795 and after 2 years, still water-tight. Sealing glass is referenced as well.....Acrylic and / or Polycarbonate ? Confused !
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Old 20-08-2015, 06:31   #21
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

AlbergSteve,

When I replaced the front Lexan windows, I used the Sika 226 Activator, Sika 209 primer, and SikaFlex 295 UV black adhesive. I also sanded the Lexan edges and surfaces that were going to have adhesive in contact. That is what Seawind recommended, and was done with the original windows. The boat is twelve years old. One of the windows was still sealed (adhered by the Sika), and the other one had some broken seal in places. Overall the Sika bond did well (probably 10 years for the one side that failed), but the window was badly crazed. In hindsight, either the GE SCS2000 Silpruf or the Dow Corning 795 would have been better products, and not rely on a primer. The Lexan windows are also held into place with screws, but they are truss screws with relatively wide heads, small diameter (#8) threads, and overdrilled holes in the Lexan. Also we have 1/4 inch of Sika behind the Lexan, and wider on the sides - by using a single-sided tape spacer. (They spec'd double sided tape, but I couldn't find it in the 1/4 in width that was also firm/non-compacting.) That's the Seawind system. If it holds for another 10-12 years, I will be happy.

The side windows are glass. Right now my issue is still trying to find a 1/4 in thick double-sided tape to hold the window in place while the Dow Corning or GE sealant sets.

Or as I am under a time crunch, I could also just cut away some of the sealant in the leaking corner and replace, and hope that lasts another year until we get back from our cruise. And then just yank it all out. Or I could just pull out the shorter window - which is the only one with problem - and rebed it, but then I have an old sealant to new sealant joint which will probably leak. And spot repairs are not in my DNA.
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Old 20-08-2015, 07:05   #22
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

It is recommended that you should no longer use screws in plastic fixed ports. Apparently the expansion and contraction of the material will cause leaks and cracks. The Dow 795 is used to glue skyscraper windows in place, so it's up to the task.
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Old 20-08-2015, 09:57   #23
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

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It is recommended that you should no longer use screws in plastic fixed ports. Apparently the expansion and contraction of the material will cause leaks and cracks. The Dow 795 is used to glue skyscraper windows in place, so it's up to the task.
The screws are required to bend the Lexan around the boat recess. They could be removed after it is set, but with the screw being smaller diameter than the hole, it's not impeding the lateral movement of the Lexan.
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Old 21-08-2015, 04:47   #24
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

The Dow 795 will fill voids. You can tape off the area around the crack that has the old stuff in it and put the 795 around and in and over and as long as it was clean it will probably hold well enough for a temp repair. On the more permanent side. The butyl tape is sticky on both sides, you can simply remove the windows clean all surfaces put the butyl tape on the boat and then stick the window back where it goes. Use the screws just put some tape on the threads. Then tape around the cracks and double seal it all up with the Dow 795. It will be set up and look great. Peel the tape off before the 795 dries though.

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Old 21-08-2015, 04:51   #25
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

Don't tighten the screws up, they are just there to keep things in place while it all dries. After a year or two you might go back and give them a turn just seal it all again. That butyl tape will never dry out sealed up in the 795 and the whole system flexes with heat expansion and contraction.

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Old 21-08-2015, 04:53   #26
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

I just read the post... To clarify butyl tape on screws and regular painters tape on the outside of the windows to keep the 795 edges clean and straight.

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Old 21-08-2015, 07:15   #27
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

Side Windows is what I am working on now. Panels are glass. No screws on them. I need something to hold the glass vertically in place while sealant dries. There is almost a two inch wide recess behind each window which is filled 1/4 inch thick with sealant. I need to use tape or something , fill the window recess, then out the window on and clean up.

So is the butyl sticky enough to hold the window until sealant dries.
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Old 21-08-2015, 09:12   #28
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

I have lots of large polycarbonate windows and here is how I do it.

First I have a significant overlap between the opening in the hull and polycarbonate material-around 2 inches all around.

Having prepared the surfaces and dry tested the fit and drilled four holes per panel I then put 1/4 inch double sided sticky foam tape on both the outer edge and the inner edge i.e. what would seen from inside the boat assuming there is a frame.

Then I will that cavity between the two rows of tape with Dow 795-not too much but not too little either. The idea is to create a moat or dam to hold the 795 in place. It makes a neat job with very little mess.

Remove the tape backing and carefully place the panel in place using the screws or bolts for alignment. There is no second chance in this. The tape itself is brutally sticky. Having another person help is almost required.

Tighened down the screws or bolts so the 795 fills all the voids which you can view from the outside. Don't tighten too much or the 795 will be squeezed out of the between the tape dams. Take your time. There is no hurry as the 795 should not be leaking out if you taped carefully.

Now or at a later time you can put a small skin coat of 795 over the sightly exposed foam tape edge on outside. Once that has dried over I mask the panel and spray paint over the outer edge for a clean look. I use silver spray paint to avoid over heating the polycarb and unnecessarily drying out the tape and 795.

The great thing about this method is you have several lines of defense against water intrusion. Plus the tape and screws or bolts hold the panel nicely against the hull or frame. This would not be necessary if you had a perfectly flat frame which mine are not.

I am going on three years without issues.
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Old 21-08-2015, 09:21   #29
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

Ok, not wanting to seem ungrateful, but the Windows I am doing now are glass no screws. Not lexan or polycarbonate. I've already done the lexan ones.

But can you tell me whose double sided 1/4 in wide tape you used. I cannot find any especially with any firmness. Thanks.
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Old 21-08-2015, 09:26   #30
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Re: Recommended Sealant/Adhesive for Installing Glass Windows

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Make sure before you rebed it that it sits flat. If you preload the window with a twist or bend the sealant will likely fail. Elastomers fail by peeling first and rarely shear or tension.
Actually I disagree with this. All of my Windows are glass except the front two are lexan because they have to bend to fit. The sealant outlasted the lexan. Ten to twelve years. Maybe the screws helped.
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