Replacing windows

I am refitting a steel hull 35ft, and thinking of removing the old windows that are held in with a wooden surround, I am leaning towards of fitting new glass with an overlap and using sikaflex to secure the windows, has anyone had any experience with this

Not sure what you're planning. You can't just glue glass windows to your boat with Sikaflex.

It holds windows in jetliners

trurtl1974 said:

It holds windows in jetliners

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Then go ahead, knock yourself out.

sean9c said:

Then go ahead, knock yourself out.

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Thanks for your input sean9c

I have some windows on my boat that are just bedded in a groove and sealed with Sikaflex 291 LOT. I re did the sealant on 2 of them and must admit was really impressed by the product. A bit of a mess to use but seals and holds very well. I guess that if my boat was a tug and to be used in very heavy seas I would tend to have stronger windows but for me it is not the case and
Sikaflex does a good job.

I replaced the curved windows in the corners of my Willard wheelhouse just that way. I did use machine screws all the way around. I kind of like the look if done neatly.

However I used MarGard Lexan not glass. Lexan can be cut, drilled, and rounded over with woodworking tools, it is 10x stronger than even tempered glass & does not sweat. Important I would think in your case, it will move as your structure works.

I don't think it would cost any more than having glass cut and edged. I used Lexan sealant and placed stick on silicone dots (1/8") around the edges to prevent squeezing out all the sealant while bending the Lexan & tightening the machine screws. Unless you are going to run a wiper on it, you don't even need MarGard, just plain Lexan will do.

Thanks brooksie I will look into Lexan it sounds like it might be a good option for the side windows

Sika and others make sealants that will work. The Sika web site is a good place to educate yourself. Be sure to read all their documentation and use the correct product and primer for the substrate and window material. Sikaflex 296 might be the one you need.

If you think about automotive window sealant you'll trust it. A car hurtling down the highway in a rain storm is encountering hurricane force winds and wind driven water.

I think there is a 3M product just for sealing windows in place...it is for skyscrapers and has been mentioned on this forum before.

Hard to believe all the applications where windows are just glued in place these days, no reason a boat couldn't do it too.

trurtl1974 said:

Thanks for your input sean9c

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OK, how about this. Jetliners don't use glass windows. Likely lexan, set in a rabbet, not simply placed on the outside of the hull. The bonded in glass windows you see in some modern boats are also set in a rabbet, indeed, sometimes using Sikaflex, but the glass has a ceramic frit fused to it for the Sikaflex to adhere to. You'll not find a sealant that will reliable adhere to glass. You could use lexan or plexiglass windows planted on the outside of your boat using Sikaflex but you will also need fasteners holding the windows on. Lexan or plexi windows will scratch and be much less durable the glass. In my experience they will also likely leak within 5 years or so and you've got a bunch of screw holes through your windows into your steel that are just asking to get wet and cause rust..
Best but most expensive solution is store bought aluminum frame glass windows.

Thanks for the info, maybe a bit more steel work to sit the glass into then

sean9c raises good points about the rabbet and ceramic coating. I think Sikaflex glazing products can be trusted. However of you are going to use them or any similar product do the research and understand what you are doing. Aluminum frame "clamp ring" windows are easier to correctly install. But they are very expensive.

Below are some links to help you get started learning.

Marine Window Bonding Using SikaFlex

Sikaflex 296 Marine Window Adhesive PDF

Bonding and Sealing Mineral Glazing

How to Bond and Seal Plastic Windows

My boat has wooden rabitted window openings.
I use Loctite Black PL Roof and flashing polyurethane from H Depot.
It is cheap, very rubbery, lots of yield so it moves- stretches and keeps the glass from leaking.

Remove glass, smear Black PL into rabbit, place glass back, smear more Black PL around the glass edge. After 2 days cure, clean edge with a razor blade and can be painted.

Loctite PL S30 Polyurethane Roof & Flashing Sealant from Loctite Adhesives

Originally, from 1970, boat had an aluminum quarter round bent to fit ontop the glass into the rabbit, then side nailed. Problems came when repairs had to be made, the nails were impossible to remove and had corroded into the aluminum.