Very Flexible Sealant (not adhesive) For Polycarbonate?

[Chenega]

Originally Posted by 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.

Dow 795 works... available at McMaster.com

[Chotu]

These two white windows were put in today. That’s pretty much a 4x8 sheet of polycarbonate spanning them. I didn’t bother making the windows smaller than 4x8 this time since the tracks can hold a 4x8 sheet no problem.

Tracks are located on the outside. So these windows aren’t going anywhere, structurally.

The white is just the protective layer of film on the outside still.

Forum doesn’t properly process exif information in pics to ensure their orientation. All my pics will be rotated wrong because of that

[Chotu]

Originally Posted by Chenega

Dow 795 works... available at McMaster.com

Jesus. Reading = 0 here I guess. Apparently we’re not even looking at pics anymore either.

[Chotu]

There is a track at the top and at the bottom now. Put on today. That holds it in place. I also used a little bit of VHB to stick it to the deckhouse better. It’s going nowhere thanks to the tracks.

See the leading edge to the left side of the pic if it’s facing correctly?

I need to squeeze some goo in there and have it tolerate massive thermal expansion, while keeping out the water that may be driven by hard winds into the crack.

The water from the top is all good. It will just roll over the top track and onto the polycarbonate. Then down off the boat.

PLEASE EXCUSE MY DECK. IT WAS LEFT ON FLORIDA FOR A FEW YEARS AND HAS THET FLORIDA MOLD ALL OVER IT. Need to bleach and scrub it.

Note: you can also see more 6 month old Dow 795 on my front window failing too.

[NYSail]

Never silicone

[Chotu]

Lastly, I have some spots where a couple of window panels butt up to each other. I need to seal that as well as that leading edge from the earlier pics.

[Chotu]

Originally Posted by NYSail

Never silicone

How come? (Other than it takes work to remove later?)

It’s required for sealing many things such as ports. You can’t install a Beckson port without using 100%?silicone or the warranty is voided.

[thinwater]

Originally Posted by Chotu

Jesus. Reading = 0 here I guess. Apparently we’re not even looking at pics anymore either.

It's a forum.

[thinwater]

Actually, silicone removes pretty with with ReMove. You can get 100% bond strength after remove and a soap and water scrub (acetone too, if you want to be sure--my test protocol was based on soap and water). Did the testing.


(DeBond for polyurethane)

[Singularity]

Originally Posted by Chotu

Lastly, I have some spots where a couple of window panels butt up to each other. I need to seal that as well as that leading edge from the earlier pics.

Have you considered Dow 795?

Kidding. I'm curious about a theory someone brought up here before, that perhaps the polycarbonate sheet may act like a light accumulator, dumping a lot (think fiber optic) of light (?UV, probably not) about the cut edge of the sheet, +/- effecting mechanicals of whatever goop is stuck right to the edge. If this were so, presumably this coupled with the large expansion/contraction woes might really tax whatever sealant you use? Just a thought to consider if this remains an ongoing problem...

[Chotu]

Originally Posted by thinwater

Actually, silicone removes pretty with with ReMove. You can get 100% bond strength after remove and a soap and water scrub (acetone too, if you want to be sure--my test protocol was based on soap and water). Did the testing.


(DeBond for polyurethane)

If silicone is the most flexible, I’ll give it a shot.

Willing to try anything at this point. At least the windows can’t fall off now. Not using the glazing stuff to hold them on anymore is a huge relief.

[Chotu]

Originally Posted by Singularity

Have you considered Dow 795?

Kidding. I'm curious about a theory someone brought up here before, that perhaps the polycarbonate sheet may act like a light accumulator, dumping a lot (think fiber optic) of light (?UV, probably not) about the cut edge of the sheet, +/- effecting mechanicals of whatever goop is stuck right to the edge. If this were so, presumably this coupled with the large expansion/contraction woes might really tax whatever sealant you use? Just a thought to consider if this remains an ongoing problem...

Maybe I should try Dow 795. Ha ha ha

I remember reading that too. It was interesting. That was in terms of degradation of the polycarbonate. Like how it was getting all cloudy and hard to see through.

I think it’s all about the thermal expansion. Oddly, even my smaller windows have an issue too.

[s/v Jedi]

The problem is not the 795 but rather installation error. The manuals are freely available and explain maximum size as well as bead thickness required for the size of window. I made spacers by curing some 795 and cutting it to length of the required bead thickness. I then superglued them in place to enforce proper bead thickness.
Next is bead shape. The nozzle needs to be cut with a V shape the depth of the bead thickness. Found that in the manual as well.

[Sailmonkey]

Originally Posted by Chotu

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.

I’ve had my hatches in for the last 8 years in the Texas/Belize/Guatemala/Florida sun with 795, nothing looks like that.

No neat story from Dow. I can say that I honestly missed what you had used. But I’ve used the same, also tried Sika with the primer. Big fail with the sika.

You want to get agitated? Fine....but that’s on you.

[Chotu]

Originally Posted by s/v Jedi

The problem is not the 795 but rather installation error. The manuals are freely available and explain maximum size as well as bead thickness required for the size of window. I made spacers by curing some 795 and cutting it to length of the required bead thickness. I then superglued them in place to enforce proper bead thickness.
Next is bead shape. The nozzle needs to be cut with a V shape the depth of the bead thickness. Found that in the manual as well.

Did you see the pics? The first one in the thread? That’s a half inch bead thickness.

Did that because it didn’t hold last time.

It’s junk. Not application error. Just junk.