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

This is getting to be a chorus on here:

Butyl tape!

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.

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?

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.

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.

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

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.

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.

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.

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.

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.

mvweebles said:

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?

Click to expand...

On the contrary... it sticks very well but best used in a clamping arrangement.

mvweebles said:

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.

Click to expand...

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.

Portage_Bay said:

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.

Click to expand...

I have tried 2 types and also prefer the Compass Marine stuff.

I like the marinehowto.com butyl tape. However if there is no mechanical connection then I wouldn’t 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 didn’t use any orimer, don’t 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.

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/tr...nterior-and-exteriorsealing/sikaflex-221.html

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.

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.

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.

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/getdocumen...1/4_Structural_Bonding_Marine_Application.pdf


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

Peter

mvweebles said:

......
What is Organic Glass? Appears to be Polycarbonite and Acryllic, though that's not exactly intuitive so maybe I'm wrong.
...........

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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/what-is-organic-glass_18314.html

Glad we all could help. Will note if you buy from industrial supply house rather than marine it’s cheaper.

Sikaflex 295 UV

mvweebles said:

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

Click to expand...

Hi Peter. I'd suggest the 3M product and glass primer. Glass is hydrophilic (attracts moisture) so this helps the bond...such as what they use when they bond glass panels in high rises. When applying the adhesives from a caulking gun cut the tip if the tub in a "V" shape and dispense almost at 9p degrees such that the adhesive comes out ina teepee or upside down "V" shape. This assumes 100% contact with the glass and frame and eliminates and air bubbles. You should be able to see all the surface preparation (very important as adhesive stick well to dirt etc but dirt etc doesn't stick well to glass etc. ) and application information and videos online at the 3M site or you tub. Mask off the frame and glass where you don't want adhesive for a clean finish. Br careful to nit touch the binding areas. Remove masking asap ...right after application. In my opinion Butyl is great but not curing it can't get dirty and be "washed" away with solvents or presure waters more easily and in extremely hot temperatures will soften and even ooze out under some pressure or movement. Butyl is typically covered up with a mechanical device/ trim. Think high rises or cars tested up to 100+ kph. Just saying. Good luck. Stay safe.

Portage_Bay said:

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.

Click to expand...

Tape off the area where you want adhesion to the glass and hit it with a sander. Instant etching.

I would use Bostik 7008. Recently I had a professional marine glass installer from Fort Lauderdale install all new glass on my boat. this is what they used. It was a flush glass installation. The 3M does not recommend any of their products to install glass in marine applications. I called them before my installation. In cars, windshield are attached using 3M Window-weld. It is not UV Stable. Car windshield are fretted. That means there is a baked-in opaque black fret around the perimeter of the windshield that protects the adhesive from UV and adds a surface for the adhesive to bite. If your installation will protect the adhesive from UV exposure it might be OK. Still,3M does not recommend that product for marine use.

cdb said:

I would use Bostik 7008. Recently I had a professional marine glass installer from Fort Lauderdale install all new glass on my boat. this is what they used. It was a flush glass installation. The 3M does not recommend any of their products to install glass in marine applications. I called them before my installation. In cars, windshield are attached using 3M Window-weld. It is not UV Stable. Car windshield are fretted. That means there is a baked-in opaque black fret around the perimeter of the windshield that protects the adhesive from UV and adds a surface for the adhesive to bite. If your installation will protect the adhesive from UV exposure it might be OK. Still,3M does not recommend that product for marine use.

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If this is in regard to 3M UV 4000 Ultraglaze, I won't question this as I've never asked 3M before. Did you see this in writing somewhere? I've never heard this before and know that this is the product that Bomar uses for glazing and recommends for reglazing the lights in deck hatches. I have used it repeatedly to glaze glass and portlights in my boats and have never had an issue over multiple years.

Hi Peter,
Having to remove and replace windows an a 36 willard aft pilot house. The boat was 30 plus years old a that point and no leaks just UV damage. A lot trouble to remove. I called Willard and they said Sikaflex was used to install all windows. So I used Sikaflex to install new windows and they are still good togo.
I have seen a lot of failures with tape. 3M I have never used so I can not say.
There are two ways to install windows. one is so you can remove easley. The other way is to put them in so you don't have to do the job again. All of this is in my opinion.
Don

I've seen a lot of tape failures too.

Boat Works Today on youtube!! Check him out. The ONLY silicon he uses is the Dow 795 and only for window glass.

Don Souza said:

Hi Peter,
Having to remove and replace windows an a 36 willard aft pilot house. The boat was 30 plus years old a that point and no leaks just UV damage. A lot trouble to remove. I called Willard and they said Sikaflex was used to install all windows. So I used Sikaflex to install new windows and they are still good togo.
I have seen a lot of failures with tape. 3M I have never used so I can not say.
There are two ways to install windows. one is so you can remove easley. The other way is to put them in so you don't have to do the job again. All of this is in my opinion.
Don

Click to expand...

Hey Don. Your W36 was the one that went to Hawaii and back in 1987, wasn't it? If so, I have some questions.

I pretty well decided on the Sika products. 295 for "organic" glass (inexplicably, this means acrylic or polycarbonate), and 296 for the side glass panes.

BTW - Marks Plastics in Corona CA (near Riverside in LA area) had a mold for the curved W36 Sedan windows so he formed up - he was kind enough to meet me at a boatyard near San Diego so I didn't have to drive from Ensenada to LA (picture is from 4 weeks ago) . Super nice guy. I don't recall exactly, but I don't think the PH version of W36 had same windows.

Peter

I spoke to 3M's technical people about this. There is an auto products division and a marine division. I spoke to both. They did email me as well. While they used to recommend certain products for marine glass installation they no longer did. I had the discussions with them about this in March. I have used 3M 4000 UV as well in other applications successfully.