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Old 27-11-2011, 20:18   #1
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Unhappy Sikaflex Not Bonded

I replaced my plexiglass windows and bedded them with Sikaflex 295uv. I did not use a primer -(too expensive) nor roughen the surface of the plexiglass as I figured that goop sticks to everything within a mile of the job and is impossible to remove. - - Wrong. After 4 months the plexiglass is coming away from the Sikaflex and now I shall have to do the job properly. Let this be a warning. ! !
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Old 28-11-2011, 02:10   #2
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Re: Sikaflex not bonded

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Originally Posted by holmek View Post
I replaced my plexiglass windows and bedded them with Sikaflex 295uv. I did not use a primer -(too expensive) nor roughen the surface of the plexiglass as I figured that goop sticks to everything within a mile of the job and is impossible to remove. - - Wrong. After 4 months the plexiglass is coming away from the Sikaflex and now I shall have to do the job properly. Let this be a warning. ! !
I found that one does need to rough up the edges of the plexi for sealers to stick. And it seems the black stuff is the worst for bonding (if that's what you used).

My windows are sunk into a register so butyl tape is my friend.
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Old 28-11-2011, 03:11   #3
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Re: Sikaflex not bonded

I build camper trailers for a living and work with Sikaflex for more than 20 years. Very important is a clean surface and on the boat I would always use a primer.
Doing the work yourself and using the right gear is still a lot cheaper when you compare what tradespeople charge to fit windows in boats . 295 should work well on your windows.
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Old 28-11-2011, 04:27   #4
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Re: Sikaflex Not Bonded

Thanks, Delmarrey, What is butyl tape?
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Old 28-11-2011, 04:46   #5
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Re: Sikaflex Not Bonded

I use a lot of PL polyurethane construction adhesive for almost everything. Here a poster says lightly sand the edge and glue the plexiglass window.

Weld Talk Message Board and Online Forum - Hobart Welders

Loctite PL Premium Polyurethane Construction Adhesive Technical Data from Loctite Adhesives

It is readily available and fairly inexpensive. I also use it for underwater. The glue will have to wear off your hands, once on your skin, so take precautions.
Mix this with wood sawdust and it makes an excellent filler.
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Old 28-11-2011, 06:02   #6
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Re: Sikaflex Not Bonded

Any used 3M's VHB tape. Have seen some positive reports on the product.
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Old 28-11-2011, 06:19   #7
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Re: Sikaflex Not Bonded

Excerpted from
“VHB Design Considerations - Structural Performance Tests”

“... Architectural metal panels assembled with VHB tapes were subjected to impact and pressure cycling tests to determine their ability to survive a hurricane or other high wind event ...
... The impacts resulted in heavy damage to the panels, frame, and stiffeners, but the VHB tapes held fast and even expanded to maintain contact with both dented surfaces ...
... VHB tapes are ideal for bonding to a variety of substrates, including most metals, glass, plastics, composites, and painted surfaces. Each product in the VHB tape family has specific features, including the ability to bond to different types of materials. Determination of whether a specific VHB tape is fit for a particular application should include adhesion testing with the actual substrates ...”

Here ➥ Sealants and Solutions : VHB Design Considerations

See also:

3M VHB (closed-cell) Acrylic Foam Tape(s) with Polyethylene Liner
http://multimedia.3m.com/mws/mediawe...6EVs6E666666--

Surface Preparation for 3M™ VHB™ Tape Applications
http://solutions.3mindia.co.in/3MCon...bute=ImageFile
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Old 28-11-2011, 06:26   #8
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Re: Sikaflex Not Bonded

May/June Good Old Boat article on building companionway doors. Benjy has good things to say about it.
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Old 28-11-2011, 06:27   #9
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Re: Sikaflex Not Bonded

You need to be using silicone for Plexiglas or a hybrid. I did a lot of research on this one you can read my article here Project Boat Zen - Understanding and Using Marine Sealants
Sanding can cause a failure in the plastic, The right primer will work but you have to use primer for plastics.
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Old 28-11-2011, 12:54   #10
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Re: Sikaflex Not Bonded

Quote:
Originally Posted by holmek View Post
Thanks, Delmarrey, What is butyl tape?
3M Weatherban Sealant Tape 5354

More threads to ponder>>>> Adhering Lexan to Wood
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