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Old 19-05-2016, 16:42   #16
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Re: Unsuccesfull windows. What to do?

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Originally Posted by carlo de leo View Post
Yes! but there's special polyurethanes for acylic also. Have to be carefull to use those sykaflex 295UV and 3M 4000UV
295UV is not specific for acrylics but suitable yes. Note that to bond to acrylic or polycarbonate, you first have to sand off any coatings to get to the material. I see people bond to coatings all the time, thinking they do it right.

3M 4000UV I recommend to stay away from for now. I have had major problems with it and read I am not alone and 3M has said they have problems with the formulation of the product. My white seam between two fiberglass parts turned orange and cracked everywhere. Stuff of nightmares.

I think Dow-Corning 795 is the go-to product for this.
Skip to the 7:00 minute mark in this video:
https://youtu.be/GnQG7eUyHxU
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Old 19-05-2016, 18:19   #17
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Re: Unsuccesfull windows. What to do?

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Originally Posted by s/v Jedi View Post
295UV is not specific for acrylics but suitable yes. Note that to bond to acrylic or polycarbonate, you first have to sand off any coatings to get to the material. I see people bond to coatings all the time, thinking they do it right.

3M 4000UV I recommend to stay away from for now. I have had major problems with it and read I am not alone and 3M has said they have problems with the formulation of the product. My white seam between two fiberglass parts turned orange and cracked everywhere. Stuff of nightmares.

I think Dow-Corning 795 is the go-to product for this.
Skip to the 7:00 minute mark in this video:
https://youtu.be/GnQG7eUyHxU
You're right, they are suitable, My mistake. But anyway, I'm not relying on the polyurethane for bonding, the 3M VHB tape is doing that. Tks
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Old 19-05-2016, 18:38   #18
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Re: Unsuccesfull windows. What to do?

IN the interest of having a high flexibility seal, wet suit type foamed neoprene with a skin on each side works very well. Use an adhesive/sealant on both sides. It allows a great deal of movement with only low stress translated to the adhesive joints. You will use this with screws, and ensure that the screws are round head, with washers under the heads and a large clearance diameter drilled in the acrylic.
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Old 19-05-2016, 18:58   #19
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Re: Unsuccesfull windows. What to do?

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Originally Posted by carlo de leo View Post
Hey guys,
need some help on this windows...
recently refited in Acrilic, they were fixed with 3M double tape (correct name?) and also used Sikaflex on edges. They are leaking in 3 points on top sides. In the picture one can see there's an off set bevel where they adapt, and is where is the leaks. I allready remade the sikaflex all around.
Possible faults: too much contraction/expansion in the acrilic, need some bolts, small offset, wrong material, what else??
How is this kind of windows is attached on traditional boats (Jeaneau, etc)?
Any help is welcome!
TKS!!!
Someone else mentione BoatWorks YouTube channel.. This might help a little
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Old 19-05-2016, 20:19   #20
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Re: Unsuccesfull windows. What to do?

Stay away from Sika and 3m sealants on this project. Hudson and Jedi got it right. Dow Corning. And the excellent video above. Do it like that and you will not have to stress about it later. Or you can be like my neighbor whom despite given good advice don't want to go through the little effort of finding the proper material and so has leaks every friggin time he tries yet another sealant. I swear, during last 3 years he has done his windows 1 or 2 times a year and it's a fail EVERY time. Last time when he touched, yes, touched, the window to check his job from few months back the window literally dropped off to the deck. Yes he did try both the recommended Sika and 3m sealants among others. Some folks always think they know what's best and refuse to take advice. Well, he will be busy with his ports for years to come.
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Old 19-05-2016, 20:56   #21
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Re: Unsuccesfull windows. What to do?

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Originally Posted by Pauls View Post
........You will use this with screws, and ensure that the screws are round head, with washers under the heads and a large clearance diameter drilled in the acrylic.
Screws are often the failure point in acrylic and with modern adhesives/sealants are not needed or desired. I do not know of any production boat that uses fasteners for acrylic ports.

Dow 795 is the sealant most recommended by experts such as Tony at Selectplastics – Selectplastics
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Old 19-05-2016, 21:37   #22
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Re: Unsuccesfull windows. What to do?

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a lot of good comments above. the supplier where I get my acrylic near San Francisco advises not to use polyurethanes with acrylic but rather the Dow Corning 795 or GE Silpruf SC-2000. And for the caulk to have the capacity to move it must have some thickness so spacing the acrylic from the cabin sides is advised.
This is the exact info I received about Acrylic...no polyurethanes. Apparently it attacks the plastic and causes crazing. I was told to use silpruf for some polycarbonate window I was installing. The regular silicon would not stick well.
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Old 20-05-2016, 01:15   #23
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Re: Unsuccesfull windows. What to do?

One more on Dow795. Might also use some screws with washers to pull it down in place.

Als be advised: do NOT use 795 beyond the expiration date. You will end up redoing it.


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Old 20-05-2016, 03:05   #24
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Re: Unsuccesfull windows. What to do?

I previously mentioned the advantage in expansion of the Dow 791 over the 795 and this is suitable as used as a sealant only and not for adhesive qualities. The adhesion is accomplished by the 3M VHB tape; however, the thickness of the tape is directly proportional to it's tolerance for expansion. My own acrylic portlights, without fasteners, are far smaller than yours, but I used the VHB 4991 tape which is the thicker among choices. I'd recommend the best adhesion that accommodates expansion and the best sealant that accommodates expansion and not to look for products doing both jobs.
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Old 20-05-2016, 07:14   #25
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Re: Unsuccesfull windows. What to do?

Question:

When using 3M VHB tape, do you see it through the plastic ? or, is the plastic coated (painted) first ? If coated, inside, or outside ?

Thanks,
JM.
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Old 20-05-2016, 07:56   #26
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Re: Unsuccesfull windows. What to do?

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Originally Posted by NahanniV View Post
Question:

When using 3M VHB tape, do you see it through the plastic ? or, is the plastic coated (painted) first ? If coated, inside, or outside ?

Thanks,
JM.
No, I dont see it cause the acrylic is very dark shade.
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Old 20-05-2016, 08:09   #27
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Re: Unsuccesfull windows. What to do?

Guys, all sugestions are really great! Thanks all! I never thought there would be Dow Corning in Brasil cause nobody uses in marine. But for my surprise, they have a big business here!
My old (20+ years) and biggest front window was screwed as and has sikaflex, works very fair and were done like Pauls said.
But the new ones, were installed with no screws like I previously describe. The problem, after hear from all, I think is the lack of space for the expansion to occur, like Barnakiel said.
As I'm not with the "stomach" to do it all again, I'm thinking in build "roof extension" to force the water drops away of the acrylic face.
What do you guys think? Picture attached..
TKS!!!
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Old 20-05-2016, 08:14   #28
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Re: Unsuccesfull windows. What to do?

https://www.dropbox.com/s/jlwzgcrli2....001.jpeg?dl=0
link for the image. Couldnt attach with the message...
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Old 20-05-2016, 08:16   #29
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Re: Unsuccesfull windows. What to do?

Quote:
Originally Posted by carlo de leo View Post
Guys, all sugestions are really great! Thanks all! I never thought there would be Dow Corning in Brasil cause nobody uses in marine. But for my surprise, they have a big business here!
My old (20+ years) and biggest front window was screwed as and has sikaflex, works very fair and were done like Pauls said.
But the new ones, were installed with no screws like I previously describe. The problem, after hear from all, I think is the lack of space for the expansion to occur, like Barnakiel said.
As I'm not with the "stomach" to do it all again, I'm thinking in build "roof extension" to force the water drops away of the acrylic face.
What do you guys think? Picture attached..
TKS!!!
Better to fix it properly
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Old 20-05-2016, 08:18   #30
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Re: Unsuccesfull windows. What to do?

Quote:
Originally Posted by NahanniV View Post
Question:

When using 3M VHB tape, do you see it through the plastic ? or, is the plastic coated (painted) first ? If coated, inside, or outside ?

Thanks,
JM.
It should be painted. The Dow 795 sticks better to the painted surface.
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