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Old 11-22-2020, 09:16 PM   #1
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What window bonding adhesive should I use?

Replacing windows on my Willard 36 - fairly large (24" x 30") panes of 3/8" tempered glass. Yard has formed an integral fiberglass frame on inside of window where the glass will sit with a mating surface against the pane of about 1-1/4" on the inside. On the outside, a fiberglass frame will sandwich the glass to capture it well.

Recommendations on adhesive/sealant? I see Dow 795 is often recommended. Thoughts?

Peter
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Old 11-22-2020, 09:45 PM   #2
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This is getting to be a chorus on here:

Butyl tape!
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Old 11-22-2020, 10:52 PM   #3
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How do the inside and outside of the frame attach to each outer or do they attach to the side of the house? If there is sufficient clamping action then I like butyl tape. It will not get hard and it stretches way more than any caulk so as the glass moves it can stretch with it.
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Old 11-23-2020, 05:43 AM   #4
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While I have heard of butyl tape for a while, I've never used it. My impression is it's a good bedding compound but has limited adhesive strength. There is no mechanical fastening to clamp the windows so need some adhesion, similar to how windows in buildings or windshields are affixed.

Thoughts?
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Old 11-23-2020, 06:10 AM   #5
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Greetings,
Mr. mv. Dow 795 is SILICONE! IMO the worst thing you can use on a boat. Since you are completely re-doing the windows AND the frames, why not design and incorporate a mechanical fastening system that will allow you to use butyl tape? You WILL have leaks in the future and you WILL have to re-bed.
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Old 11-23-2020, 06:34 AM   #6
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How are auto windshields attached? At best, they have trim pieces and virtually no mechanical clamping. And are relatively large expanses of glass.

Just curious. I see 3m makes an adhesive for windshields but I have never personally used it.
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Old 11-23-2020, 06:42 AM   #7
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BTW - what flavor of butyl tape for bedding deck hardware such as cleats and such? I see McMaster Carr has a zillion products listed as butyl tape, including pipe thread tape similar to Teflon tape.

Any specific recommendations? Thanks in advance.

Peter
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Old 11-23-2020, 07:30 AM   #8
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I've done some research and thinking on the subject. I don't have any firm ideas yet. It seems to me that automotive sealants are the way to go. Especially for your situation where there is no good physical clamping. I think about it a car at highway speeds in the rain encountering a mild head wind, it is experiencing hurricane conditions.

Finding the correct adhesive could be as simple as calling an auto glass company.

The wrinkle is that a car's windshield glass has ceramic dots embedded in the glass for the adhesive to grab. I don't think there is any adhesive that will bond to glass.

A possible work around might be to etch the glass at the edges. Hobby shops will have the supplies needed. It would be the same stuff crafters use to etch images into glass.

At this point just thinking out through. No experience yet.
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Old 11-23-2020, 07:33 AM   #9
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re butyl tape.

https://marinehowto.com/bed-it-tape/

I've used it and am satisfied. I've tried the stuff from RV suppliers and been disappointed.
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Old 11-23-2020, 08:48 AM   #10
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We had to replace a frameless window (starboard pilot house side window) on our Carver 450 Voyager this passed August. We used the adhesive recommended by Carver.
Dow Automotive-U-418 Beta Seal Glass Adhesive

It has held up well so far.

We purchased the window glass from a local glass supply company because the original supplier of the 450 Voyager glass was in England and due to COVID we were not able to source the glass in a timely manner. The glass we purchased locally does not have the black stripe and black dots that the original glass had and that you see in Automotive windshields. We were told those details are to hide the sealant from sunlight and protect it. We are planning to add paint to the glass to cover the sealant from sun and from view. Hoping this window stays in place for many many years.
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Old 11-23-2020, 09:02 AM   #11
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I got back to my computer and found the old bookmarks. This is the adhesive recommended to me by an experienced shipwright. Sikaflex 296 Black Marine Glass Window Adhesive and the manufacturer's web site Sikaflex 296. As I said above, no experience with it yet, just thinking it through.
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Old 11-23-2020, 09:45 AM   #12
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I would definitely not use butyl tape as it has no structural or adhesive strength. I know there's an external frame to capture the window but you want the window firmly glazed in. There are really only 3 products that should be used. for window glazing. Dow 795, GE 4000 Ultraglaze, and a Sikaflex product that requires a primer and is expensive (not sure of #). The Down and GE products are readily available, don't require primer, and are not terribly expensive. Bomar uses the GE product to glaze their hatches. I have used it with great success to reglaze the massive side windows on my sportfish. And don't listen to folks who say "no silicone", while I would generally agree on this, in this case these products are purpose made for this exact application.
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Old 11-23-2020, 09:50 AM   #13
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Quote:
Originally Posted by mvweebles View Post
While I have heard of butyl tape for a while, I've never used it. My impression is it's a good bedding compound but has limited adhesive strength. There is no mechanical fastening to clamp the windows so need some adhesion, similar to how windows in buildings or windshields are affixed.

Thoughts?
On the contrary... it sticks very well but best used in a clamping arrangement.
Quote:
Originally Posted by mvweebles View Post
How are auto windshields attached? At best, they have trim pieces and virtually no mechanical clamping. And are relatively large expanses of glass.

Just curious. I see 3m makes an adhesive for windshields but I have never personally used it.
I do believe the black sealant used in auto windshields is butyl caulk and could be a good choice. You may want to build a jig to hold the pieces together at a fixed thickness dimension until it cures. Also good idea to mask the glass & frame so "tooling" the seal to a smooth & uniform look doesn't get it all over. Butyl Sealand can be messy if not careful but should be an excellent choice for the application.
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Originally Posted by Portage_Bay View Post
re butyl tape.

https://marinehowto.com/bed-it-tape/

I've used it and am satisfied. I've tried the stuff from RV suppliers and been disappointed.
I have tried 2 types and also prefer the Compass Marine stuff.
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Old 11-23-2020, 11:42 AM   #14
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I like the marinehowto.com butyl tape. However if there is no mechanical connection then I wouldnít use butyl. I have used Sika 295 UV to stick some plexi on my venturi windshield. It has been there for 4 years now with no issues. I didnít use any orimer, donít think that it was called for. I have used the Sike primer when I caulked the teak toerail to the deck. It was about $80 for the primer, but it has stuck for 4 years now so it was absolutely worth it.
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Old 11-23-2020, 12:49 PM   #15
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Believe sisterships have been using Sikaflex on large fixed port lights with success. These boats commonly see a lot of UV, variations in ambient temp and boarding seas. Think this version is the one
https://gbr.sika.com/en/industry/tra...aflex-221.html
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Old 11-23-2020, 02:59 PM   #16
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I did our windows and used Locktite polyurethane sealant. Purchased at HD. They bought out somebody who was recommended on the Grand Banks forum.

It is also a fairly strong adhesive. Cleans with mineral spirits.

Got to my blog, grandbankschoices and you can see the process.

Paintable, I used Awlgrip. Gives a little. Can fill gaps of probably 1/4".

A bitch to get off everything.
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Old 11-23-2020, 03:04 PM   #17
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As a note, I taped everything for easy clean up.

Allowed me to get a 1/8 caulk seam and paint in one pass.

With Awlgrip GB white the frames look like they are molded into cabin sides.
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Old 11-23-2020, 04:06 PM   #18
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Second on the Sikaflex 296 Black. A friend of mine is a professional glass guy and we removed and resealed one of my windshields with it.
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Old 11-24-2020, 09:08 AM   #19
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First, thanks for the responses. Very helpful.

Second, I tried to contact Sika Adhesives. Impossible to find the right person for marine, so I gave up. I too have liked Sika over the years. One question I had was difference between 295 and 296. Documentation states 295 is for "Organic Glass." What is Organic Glass? Appears to be Polycarbonite and Acryllic, though that's not exactly intuitive so maybe I'm wrong. 295 is a UV stable silicone.

Third and for me most useful, I found the attached install/product sheet. Gives information on thickness of bead, back-fill requirements, etc.

https://dnk.sika.com/dms/getdocument...pplication.pdf


Again, many thanks to all - I would not have found this info had y'all not started me down the path.

Peter
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Old 11-24-2020, 09:48 AM   #20
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Quote:
Originally Posted by mvweebles View Post
......
What is Organic Glass? Appears to be Polycarbonite and Acryllic, though that's not exactly intuitive so maybe I'm wrong.
...........
I think you've got it right, organic glass is not glass glass if that make sense. Here's one link that explains it. https://ask.okorder.com/questions/wh...ass_18314.html
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