Very Flexible Sealant (not adhesive) For Polycarbonate?

[Chotu]

Originally Posted by Sailmonkey

What material is in there now?

I’d also suggest 795, it’s meant for hi-rise windows.

What is there now?? Dow 795. I’ve said that 3x now. Are you suggesting it again because you didn’t look at the pics of it after 6 months or... because it has a neat story about holding skyscraper windows in? VHB tape shares that neat internet legend too. Both failed. You’re suggesting I just keep putting that stuff on over and over and over?

Sorry. Getting agitated at having people read things on the internet and regurgitate them. This is a real situation. Not something a cute story and a can of hope can fix. All the details are above in the thread. Many are not reading them or even looking at the pics of the “skyscraper” adhesive/sealant Dow 795 failing. It’s right in the pic.

[Chotu]

Originally Posted by jhulmer

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


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

Thank you very much. I’ll check these out.

[Chotu]

By the way, is anyone here in the glazing business? What do you use as a sealant?

[zstine]

Since it is sitting in a (fixed?) channel, I'm guessing there will be less thickness to the sealant.. so even more likely to fail with expansion.


i know I said this before. Check out these Trim seal options. Can be removed. Should be ~$2per ft. not sure how that compares to a tube of sealant with a heavy bead.? 888-874-6565
https://www.trimlok.com/rubber-extrusion/trim-seal

[Bill O]

Originally Posted by Chotu

6 months in the south Florida Sunshie.

LARGE 48 x 48 polycarbonate windows though. Massive thermal expansion.

We have several hatches (largest is 26x31") where we set the plexi in spot w/the 795 10 years ago and are still doing fine. (plexi to wood)

To hold the acrylic in spot the edges were set in a frame to allow for a min. of 1/4" of a 795 bead on the edge and the underside of the edge to form a "L" bead of 795 (need stand offs to hold the acrylic up while it sets).

This "L" type seal was what they described back then for 795 and now they have a whole technical manual for their sealants and glazing compounds. https://www.dow.com/documents/en-us/...df?iframe=true

Maybe you can find something better described in the manual to use on polycarbonate.

[Emmalina]

I used 795 after getting bored with Sikaflex And its been in the tropical sun for the last 2 years and is doing great ! Plexi to stainless !

[Cheechako]

Uhhh....Many people are suggesting Dow 795 which is what he has the problem with!

Some said Polyurethane. Poly (5200) turns hard eventually in the sun. Eventually so much so it will start to crumble after 5+ years. So not good for that job.

Those rubber gaskets have a name /terminology, but I forget what it is. Here's a story though: As a builder, we put windows in some military vessels with that. A wave popped the window into the helm station on one during testing, not a big wave but a solid hit to the pane. This window was maybe 42 x 42" so pretty big. May be ok for smaller windows.

[Cheechako]

Originally Posted by Chotu

By the way, is anyone here in the glazing business? What do you use as a sealant?

Maybe call someone? Here's some info that may or may not be of use:
I did some caulking with my usual 3M 5200 when I was in Florida. It was hot and muggy when I did it, but I protected from direct sunlight.
Strangely, the stuff cured nothing like 5200 usually cures. It was outgassing too fast I think, a bit brittle for fresh 5200 and had tiny bubbles throughout.

One wonders if that was your problem with Dow 795?

[BruceS]

Butyl Mastic like they use to seal coolrooms should work. Remains totally 'fluid' under a firm skin which can be painted. Used extensively in building local houseboats using coolroom panels. (hot/cold/expand/shrink)

[CarlF]

I really don’t know anything that’s as good as 795 for frameless plexi - and I’ve tried just about everything over the years. I’ve seen 795 fail for three reasons::

1) The caulk bead was too thin for the thermal expansion. 1/4” is usually enough and the OP’s picture looks plenty thick

2) The caulk was put in very thick on a very hot day. On hot days I’ve been told it’s better to apply half thickness and then 1/2 the next day

3) The tube was past the expiration date printed on the tube (which is usually less than six months when I bought mine). You have to be really careful to get fresh tubes.

Here is the 795 technical manual
https://www.dow.com/documents/en-us/...df?iframe=true

[Cheechako]

Originally Posted by BruceS

Butyl Mastic like they use to seal coolrooms should work. Remains totally 'fluid' under a firm skin which can be painted. Used extensively in building local houseboats using coolroom panels. (hot/cold/expand/shrink)

I don't see this filling a gap smoothly like his picture...? wrong?

[Chotu]

Originally Posted by zstine

Since it is sitting in a (fixed?) channel, I'm guessing there will be less thickness to the sealant.. so even more likely to fail with expansion.


i know I said this before. Check out these Trim seal options. Can be removed. Should be ~$2per ft. not sure how that compares to a tube of sealant with a heavy bead.? 888-874-6565
https://www.trimlok.com/rubber-extrusion/trim-seal

Oh I’m definitely listening.

This is great. I don’t even care about cost on this. The number of hours I’ve spent doing these windows over and over and over is enough to make me want to puke. Significant hours of my life wasted and I can’t get it back. Money is not the issue at all. Time is

Who would have thought my sliding windows would work so much better than fixed?

The sliding windows employ trim seal like this and it works flawlessly. Like a car window.

[Chotu]

Originally Posted by Cheechako

Uhhh....Many people are suggesting Dow 795 which is what he has the problem with!

Some said Polyurethane. Poly (5200) turns hard eventually in the sun. Eventually so much so it will start to crumble after 5+ years. So not good for that job.

Those rubber gaskets have a name /terminology, but I forget what it is. Here's a story though: As a builder, we put windows in some military vessels with that. A wave popped the window into the helm station on one during testing, not a big wave but a solid hit to the pane. This window was maybe 42 x 42" so pretty big. May be ok for smaller windows.

See, my windows are now already in place. (As of today, in new aluminum tracks). These tracks are on the top and bottom of the windows. Nothing is going anywhere. I don’t need any structural anything.. I just need a sealant now for the parts of the windows that are not the top and bottom. As I don’t want to put tracks all around since I won’t be able to slide the windows out to replace someday.

I’ll take some pics...

[thinwater]

can you make the windows smaller? My PDQ had large salon windows, but they were divided into manageable segments. No problems.

[wingssail]

I've had a similar problem sealing and attaching acrylic 31x31 panes to aluminum frames. I have used sika 295 and a variety of other products. I have not been able to obtain Dow 795, but I may try that next if I can get it.

I have used wide gaps and "L" gaps with stand-offs, basically everything. I still get cracks like Chotu shows within a 6 months or less in Mexico.

So here is my latest theory: The thermal expansion coefficient of acrylic is such that there is a lot of expansion and shrinkage. It is, in my guess, the shrinkage which breaks the seal and causes the cracks. We put the acrylic in while hot and eventually, on a cool day or night, it shrinks. Next time I'll put it in on a cool day. I think the seal will withstand pressure better than tension.

As for Butyl Tape. I used LifeSave Butyl Caulking tape on another acrylic panel. It was fine until another really hot spell and then the Butyl melted and ran out like wet paint.