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Old 02-24-2013, 01:16 AM   #1
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Sealant question

Calling all sealant experts....

I need to do a lap joint on lexan pilot house windows. By that I mean a leveled bead that lays flat on the lexan. My concern is adhesion. From my Fisheries Supply catalog, I see Sikaflex 295 says to "avoid feather edging over the glass", which is basically what I need to do. The bead I want to lay down will go from the window frame (about 1/8" proud of the lexan) to about 1/2" from the frame on the lexan. Suggestions on products?

Many thanks.
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Old 02-24-2013, 06:41 AM   #2
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If you tape the Lexan for the edge of the bead you will end up with an edge on the bead that's the thickness of the tape. This may help avoid the feathering issues, although the edge will catch and trap dirt.

You could also tape the edge of your bead to protect the Lexan that will be below the bead and then "etch" the 1/2" of exposed Lexan with fine sandpaper to enhance the adhesion of the bead.

These ideas are based only on logic and what I think the end result will be. I have not had any experience with what you are trying to do.
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Old 02-24-2013, 07:31 AM   #3
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Greetings,
Mr Delfin. How about a call to Sikaflex and ask their opinion? That feather edge situation may be systemic with any product. Is there any option of re-engineering the profile of that particular joint thus eliminating the feather edge?
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Old 02-24-2013, 09:34 AM   #4
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Carl,
As much as I dislike Silicone it may be the best sealer for your app. Coatings like paint and sealer adhere to their favorite surfaces. Some like porous surfaces like bare wood and others like non-porous surfaces like glass. They make fish tanks out of glass and plastic and put them together w silicone. I'm sure one must clean the surface properly but I think Silicone would be best on the Lexan. Ask a fish tank builder.
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Old 02-24-2013, 12:02 PM   #5
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Marin, that makes perfect sense. I suppose if I use paper tape, the hard edge wouldn't be feathered. Thanks.

RT, what is the point in asking experts for help? Takes the fun, excitement and that element of the unknown out of the project, don't you think? I believe Marin's observation is correct on the feather edge, which probably just means avoiding a no tape edge. There's a primer for some of the Sika products designed for glass/acrylic that I'll look into as well.

Thanks Eric. I also hate silicone since it seems to remain a dirt magnet forever, but I agree, it would stick if cleaned well first.
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Old 02-24-2013, 12:43 PM   #6
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Delphin-- I'm certain you know this from experience, but if you elect to mask the Lexan side of your bead remember to pull the tape almost immediately after applying and smoothing the bead. If the sealant is allowed to cure at all you run the risk of pulling up your bead, or the edge of it, when you pull the tape.

And don't forget to pull the tape up and over toward the bead, not straight up. This will help encourage any threads of wet sealant that lift up with the tape to fall back on the bead, not onto the clean Lexan below it.
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Old 02-24-2013, 12:59 PM   #7
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Quote:
Originally Posted by Marin View Post
Delphin-- I'm certain you know this from experience, but if you elect to mask the Lexan side of your bead remember to pull the tape almost immediately after applying and smoothing the bead. If the sealant is allowed to cure at all you run the risk of pulling up your bead, or the edge of it, when you pull the tape.

And don't forget to pull the tape up and over toward the bead, not straight up. This will help encourage any threads of wet sealant that lift up with the tape to fall back on the bead, not onto the clean Lexan below it.
Marin's first recommendation was correct, as is this post! The Sika 295UV is the best product for this use.... I rebedded evey window on our boat with it, and my windows are glass...by pulling the tape before the product kicks....you avoid any lifting of the 295...

The product is easy to work....and here's a tip.... when you get your bead smooth or the way you want it....back off, leave it alone!! That I learned by experience....
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Old 02-24-2013, 02:40 PM   #8
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Quote:
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Marin's first recommendation was correct, as is this post! The Sika 295UV is the best product for this use.... I rebedded evey window on our boat with it, and my windows are glass...by pulling the tape before the product kicks....you avoid any lifting of the 295...

The product is easy to work....and here's a tip.... when you get your bead smooth or the way you want it....back off, leave it alone!! That I learned by experience....
If you remember, about how much time did you let it kick off before removing the tape?
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Old 02-24-2013, 02:43 PM   #9
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Quote:
Originally Posted by Marin View Post
Delphin-- I'm certain you know this from experience, but if you elect to mask the Lexan side of your bead remember to pull the tape almost immediately after applying and smoothing the bead. If the sealant is allowed to cure at all you run the risk of pulling up your bead, or the edge of it, when you pull the tape.

And don't forget to pull the tape up and over toward the bead, not straight up. This will help encourage any threads of wet sealant that lift up with the tape to fall back on the bead, not onto the clean Lexan below it.
Thanks Marin. Good advice, and I'll follow it. By the way, the name is Delfin, not Delphin. Delphin is the name of a French whorehouse.
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Old 02-24-2013, 03:25 PM   #10
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GE inventor of both Lexan and silicone RTV has a product specificly for Lexan. It is available at HDepot, for one, and is cheap.
I have used this and would again
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Old 02-24-2013, 04:39 PM   #11
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Thanks Marin. Good advice, and I'll follow it. By the way, the name is Delfin, not Delphin. Delphin is the name of a French whorehouse.
I knew that but my fingers forgot. Sorry. Probably should have just said "Carl."
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Old 02-24-2013, 04:59 PM   #12
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Quote:
Originally Posted by Delfin View Post
If you remember, about how much time did you let it kick off before removing the tape?

The first time I used it....I pulled it off too soon....about 30 minutes after I was done.... WHATTAMESS!!

On the following windows....I waited about an hour or so to let it get a decent skin on it....and it came off far better....a lot less mess on my hands from the tape.... Yes, it pays to wear nitrile gloves..... Lesson learned!!

If your feathering at the edge of the tape is really thin...as in almost nothing there...you can leave it on til the next day...and there is no mess.

Now...I should add...I used the stuff in the bright and hot Florida sun...and once I figured out how not to make a mess...there was virtually no cleanup other than throwing away the used tape.

Oh, and if you "oops" like I did...and managed to get some outside of the taping....leave it be til it sets up....and just peel it off with a single edge razor blade....
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Old 02-24-2013, 06:49 PM   #13
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I knew that .....
How did you know that? have you been to France?
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Old 02-24-2013, 08:38 PM   #14
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How did you know that? have you been to France?
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Old 02-24-2013, 10:16 PM   #15
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I would stay completely away from silicone. No matter how good abond you think you have today, next year it will have come off in enough places and remain in others, to let dirt and water under it and it will look awful and leak.

Lexan is one of the materials that you should use crazy glue (cyano-acrilate) to bond. If you want it to adhere permanently, that is.
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Old 02-24-2013, 11:37 PM   #16
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How did you know that? have you been to France?
Bwahahahahahaha :-D
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Old 02-25-2013, 12:35 AM   #17
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Quote:
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The first time I used it....I pulled it off too soon....about 30 minutes after I was done.... WHATTAMESS!!

On the following windows....I waited about an hour or so to let it get a decent skin on it....and it came off far better....a lot less mess on my hands from the tape.... Yes, it pays to wear nitrile gloves..... Lesson learned!!

If your feathering at the edge of the tape is really thin...as in almost nothing there...you can leave it on til the next day...and there is no mess.

Now...I should add...I used the stuff in the bright and hot Florida sun...and once I figured out how not to make a mess...there was virtually no cleanup other than throwing away the used tape.

Oh, and if you "oops" like I did...and managed to get some outside of the taping....leave it be til it sets up....and just peel it off with a single edge razor blade....
Thank you, that is helpful, as are others' advice. I'll let you all know how it turns out!
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