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Old 20-11-2020, 07:31   #1
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Very Flexible Sealant (not adhesive) For Polycarbonate?

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!
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Old 20-11-2020, 07:48   #2
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

I have found that the polyurethane based caulks generally have the best adhesion, flexibility, and lifespan. They are usually pretty pricy but seem to work the best. I like the Sikaflex products.
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Old 20-11-2020, 08:50   #3
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

How long did it take to do this? I am getting ready to replace my windows and was planning on using 795 as it seems to be the recommended product.

Thank
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Old 20-11-2020, 08:57   #4
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

Quote:
Originally Posted by flee27 View Post
How long did it take to do this? I am getting ready to replace my windows and was planning on using 795 as it seems to be the recommended product.

Thank
Foster
6 months in the south Florida Sunshie.

LARGE 48 x 48 polycarbonate windows though. Massive thermal expansion.
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Old 20-11-2020, 10:35   #5
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

Chotu,
The best product for that job is Dow Corning 795. I purchase mine through a local industrial supply and it is about $7 for a regular caulk gun size tube.
Here is some information that I have put together on this sort of issue.
Best regards,
Steve Baum
Homeport of Portsmouth, Virginia, USA

Installation pdf.pdf Views: 41 Size: 59.1 KB ">F24-IRJDSUNE9932123321222xxeww-Window-IRJDSUNE9932123321222xxeww-Installation-IRJDSUNE9932123321222xxeww-pdf.pdf
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Old 20-11-2020, 10:37   #6
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

Chotu, I think you might want to look into a gasket, vice sealant. Quick google search came up with this 'locking gasket'.. worth a phone call
https://www.trimlok.com/rubber-extrusion/locking-gasket
https://www.mcmaster.com/window-gask...ocking-slot-6/
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Old 20-11-2020, 10:45   #7
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

Quote:
Originally Posted by srbaum View Post
Chotu,
The best product for that job is Dow Corning 795. I purchase mine through a local industrial supply and it is about $7 for a regular caulk gun size tube.
Here is some information that I have put together on this sort of issue.
Best regards,
Steve Baum
Homeport of Portsmouth, Virginia, USA

Attachment 227302
assuming you did not read the post OR look at the picture (of Dow 795)
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Old 20-11-2020, 10:47   #8
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

Quote:
Originally Posted by zstine View Post
Chotu, I think you might want to look into a gasket, vice sealant. Quick google search came up with this 'locking gasket'.. worth a phone call
https://www.trimlok.com/rubber-extrusion/locking-gasket
https://www.mcmaster.com/window-gask...ocking-slot-6/
This is a pretty good idea. A gasket would work great. I have already put the windows that completely failed into tracks which wonít be affected by the thermal expansion. The gaskets could keep the water out like they do on my sliding windows.
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Old 20-11-2020, 11:08   #9
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

I use Silpruf SCS2000. They use this for installing huge windows in skyscrapers without fastners.

Islland Packet has relied on this for years.
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Old 20-11-2020, 11:24   #10
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

I'm a fan of Butyl in the form of butyl tape. Flexible, easy to clean up, sticky as heck. We use for bedding all sorts of deck items including hatches, windows, chain plate covers, etc.

I like to use a heat gun to help it set, screw down gently and follow up a few times in the next few days to screw down further and it will seal well and last a long, long time.
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Old 20-11-2020, 11:49   #11
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

I think I should clear up some terminology.

Adhesive: Holds things in place by bonding to them. Intended to act as a structural component. It’s what holds skyscraper windows in place.

Bedding compound: Acts as a sealant in conjunction with traditional hardware. Basically is a soft gasket material you use traditional hardware to tighten against to make a seal and keep water out.

Sealant: Something you use seal cracks and gaps to keep water from dripping into these cracks and gaps.

Many products are more than one of these at a time. Dow 795 for instance. It’s an adhesive sealant. Holds your piece in place AND keeps water out (if it doesn’t fail like it does for me).

Sealant/bedding compound. Silicone. It can be used for bedding and sealing.

I am looking for a very good sealing product that is applied over gaps and cracks to prevent water from getting into gaps and cracks. I don’t need a bedding compound (butyl) and I don’t need a structural adhesive (3m 5200)

I need a sealant to close gaps and cracks to keep water out.

The window is held in place by tracks now so it can expand and contract at will and not fall off when Dow 795 and VHB tape fails.

I have a crack at the edge of the window toward the bow to fill. I have a transition from the hull to the upper aluminum track to fill. I’m filling them to keep water from entering them.

The leading edge of the window toward the bow needs something incredibly flexible since it will be doing the usual thermal expansion thing that killed Dow 795 and VHB tape.

The windows do NOT have fasteners. They are held in place by upper and lower tracks.
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Old 20-11-2020, 12:22   #12
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

Did you use a bond breaker on the back of the channel that is filled? I think that you are supposed to use a bond breaker or a backing rod for this type of bead.
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Old 20-11-2020, 12:28   #13
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

Quote:
Originally Posted by Thumbs Up View Post
Did you use a bond breaker on the back of the channel that is filled? I think that you are supposed to use a bond breaker or a backing rod for this type of bead.
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
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Old 20-11-2020, 12:43   #14
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

What material is in there now?

Iíd also suggest 795, itís meant for hi-rise windows.
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Old 20-11-2020, 12:55   #15
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Re: Very Flexible Sealant (not adhesive) For Polycarbonate?

Sikaflex 295
https://www.mcmaster.com/6937T8/


DOW 995
https://www.mcmaster.com/dow-corning...sives-sealants
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