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Old 21-11-2020, 07:15   #61
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

I have seen car trim strip used to make things look nice. Comes in various widths (& colours).
Something like this.https://www.teplicp.com/index.php?ma...ucts_id=434077
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Old 21-11-2020, 08:15   #62
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

Problem solved!

Credit to Tupaia and Zstine.

This will take care of the forward gap and a different car trim or similar can take care of the butt joint.

Best of all? I’ll NEVER have to redo sealant/caulking on this boat’s cabintop windows. After all the time spent doing and redoing sealant on these windows, I think I’ve earned that. Ha ha ha.

Very happy with the outcome of the thread. Thank you.

https://www.amazon.com/gp/aw/d/B07HN...b_b_prod_image
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Old 21-11-2020, 08:50   #63
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

Quote:
Originally Posted by Chotu View Post
Attached, please find some pics of what Dow 795 does when used as a sealant with large pieces of polycarbonate.

Is there a better, more flexible and resilient sealing material I can use just to seal the gaps? Not looking to take any structural load with the sealant. Just looking for something that will not crack as things expand and contract. Something that stays stuck on the polycarbonate and the hull but gives really nicely in between the two.

Thanks!
I've had this problem due to expansion/contraction of the polycarbonate window, especially on the sunny side of my boat. I've had to reseal my windows twice; originally used 4200 not so good after a year or more, then switched to 795. First taped off the cabin trunk around the window edge about 3/16 to 1/4 inch then applied a generous amount of sealant along the 9mm window edge, then used a rubber caulking finish tool to spread sealant and allow to over hang the edge of the window. Pull the border tape off within a few minutes otherwise one will pull up the sealant. After sealant cured trim the over hanging cured sealant with a razor blade. In time the sealant separates creating small leaks that develop at the outer edge of the window in specific areas. Frustrated, I then used Permatex black silicone adhesive sealant bought at auto part store to add to the small leaks, and it has worked through the rest of the summer. When I reseal the window again if necessary, will use 795 as have a tube waiting. Be sure to clean the area well with denature alcohol or acetone prior to application. I understand some people think that silicone should nor be allowed on a boat, l but in this case it worked.
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Old 21-11-2020, 12:05   #64
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

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Originally Posted by Chotu View Post
Aluminum Channels were just added. They are not filled with anything but polycarbonate. I had wood/epoxy channels originally which did fine, until they rotted.

Dow 795 and VHB failed when they were used structurally. Now back to channel to do the structural stuff.

Just looking for the best sealant to fill a gap and contend with huge thermal expansion
You need to look up backing rod and bond breaker tape. It is incorrect to just fill a big gap like that. backing rod gives you an hourglass bead profile which is more flexible. Standard practice (caulking 101)!
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Old 21-11-2020, 12:11   #65
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

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Originally Posted by Thumbs Up View Post
You need to look up backing rod and bond breaker tape. It is incorrect to just fill a big gap like that. backing rod gives you an hourglass bead profile which is more flexible. Standard practice (caulking 101)!
Absolutely. I just learned this by googling all this stuff. The diagrams show you have to let the sealant slide freely in the back.

Thatís good for the butt joints, but what about the forward gap? I ordered a gasket for that.

Any tips on how to do the forward gap with caulking?
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Old 21-11-2020, 12:21   #66
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

From the DOW technical manual: Three-sided adhesion limits the amount of movement that a joint can accept without inducing a
tear. Three-sided adhesion can be eliminated by the addition of a bond breaker tape or backer rod.
With three-sided adhesion, no more than Ī15% movement can be accommodated.
 A properly designed moving joint with a 2:1 width to depth ratio will accommodate more
movement than a thick joint (i.e., 1.5:1 or 1:1 ratio). Sealants are designed to deliver optimum
performance when the joints are shaped like an hourglass and use the 2:1 ratio
Look around page 56 https://www.dow.com/documents/en-us/...df?iframe=true
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Old 21-11-2020, 12:30   #67
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

Quote:
Originally Posted by Thumbs Up View Post
From the DOW technical manual: Three-sided adhesion limits the amount of movement that a joint can accept without inducing a
tear. Three-sided adhesion can be eliminated by the addition of a bond breaker tape or backer rod.
With three-sided adhesion, no more than Ī15% movement can be accommodated.
 A properly designed moving joint with a 2:1 width to depth ratio will accommodate more
movement than a thick joint (i.e., 1.5:1 or 1:1 ratio). Sealants are designed to deliver optimum
performance when the joints are shaped like an hourglass and use the 2:1 ratio
Look around page 56 https://www.dow.com/documents/en-us/...df?iframe=true
Yeah, but that’s not the joint of the forward section of the new window.

This is the joint of the forward section.

That’s the gap I need to seal now.

I could put more track on the forward edge, but it needs to be removable so I can pull that sheet out to replace someday If necessary.
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Old 21-11-2020, 12:31   #68
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

And a pic of the new window in its tracks.
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Old 21-11-2020, 17:52   #69
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

I am sure most of you Sailors also navigate a motor car--You may notice a black band around the edge of your front and rear screens--This is not for
decoration-- It protects the underlying adhesive from UV degradation-
Windscreens last the life of the car!!!--use the same adhesive to stick a mirror to your screen without UV protection and it will fall off very quickly with the adhesive crumbling--Just a thought!!
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Old 21-11-2020, 18:34   #70
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

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Originally Posted by CORALSEA TRAMP View Post
I am sure most of you Sailors also navigate a motor car--You may notice a black band around the edge of your front and rear screens--This is not for
decoration-- It protects the underlying adhesive from UV degradation-
Windscreens last the life of the car!!!--use the same adhesive to stick a mirror to your screen without UV protection and it will fall off very quickly with the adhesive crumbling--Just a thought!!
You can see these black bands in the picture above your post.

So what are you getting at? What advice do you have for sealing the forward gap? Keep 100% of the sealant out of the light?

Because the 795 and VHB both failed from behind the band the 3 other times o used them
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Old 22-11-2020, 00:18   #71
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

There are many opinions when it comes to windows - we have 2 meter x 650 mm sheets of polycarbonate wrapped around our bridge deck cabin - we were advised by the manufacturer to use a product from Adheseal - its an exceptionally stretchy silicone effectively unaffected by UV. I feel though the key to whatever you choose is to make sure your opened cracked surfaces are 100% clean and preferably keyed back finished off with isopropanol before any sealant is applied. Apply the sealant on during an average temperature as polycarbonate has relatively large expansion coefficients so you want it neither undergoing compression or pulling apart your gap. If I were you I'd feel happier carving back the existing sealant.
This is at least the Australian supplier: https://www.adheseal.com.au/shop/adh...sia-sealproof/
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Old 22-11-2020, 00:56   #72
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

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Originally Posted by allatsea99 View Post
There are many opinions when it comes to windows - we have 2 meter x 650 mm sheets of polycarbonate wrapped around our bridge deck cabin - we were advised by the manufacturer to use a product from Adheseal - its an exceptionally stretchy silicone effectively unaffected by UV. I feel though the key to whatever you choose is to make sure your opened cracked surfaces are 100% clean and preferably keyed back finished off with isopropanol before any sealant is applied. Apply the sealant on during an average temperature as polycarbonate has relatively large expansion coefficients so you want it neither undergoing compression or pulling apart your gap. If I were you I'd feel happier carving back the existing sealant.
This is at least the Australian supplier: https://www.adheseal.com.au/shop/adh...sia-sealproof/
This has a very good elongation at 700%. Exactly the type of sealant I was asking about. Thanks
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