Very Flexible Sealant (not adhesive) For Polycarbonate?

[Sherpa17]

www.alro.com has interesting graphics regarding thermal expansion in plastics.

[RKsailsolo]

Originally Posted by Sherpa17

www.alro.com has interesting graphics regarding thermal expansion in plastics.

Alro has a big website. C.an you link us to your suggested graphic?

[Nightsky]

Admittedly, I only read thru the first 3 pages of this thread. So this may have already been suggested. I use Capt Tolly's Creeping Crack Cure. It wicks in to the cracks to seal. My experience has been that I sometimes have to go over more than once or twice to stop the leaks, depending on how deep the crack is.

[Sherpa17]

TUFFAK section of Alro plastics.

Originally Posted by RKsailsolo

Alro has a big website. C.an you link us to your suggested graphic?

[Tanqueray]

Originally Posted by Chotu

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!

So I can’t really tell what your first photo shows...and in your description, you talk about adding channels top and bottom.

So, what is the current condition you are trying to correct? I won’t mention 795, but if you changed the set up...maybe it is not the wrong choice.

In the photo, it looks like pieces or plexi, butted together with a bead of 795 in the seam...that isn’t right I assume...but that is what I see...

Greg

[john manning]

Hi,
I think you are looking at this problem the wrong way. From your photo it appears that there is a clean separation between your sealant and the bottom edge. That means the adhesion was not sufficient. If the sealant was not flexible enough it would have separated in the middle not at the edges.

My opinion is that the flexibility outlasted the adhesion.

[moidus]

I used GE SSG4000 UltraGlaze Silicone Structural Glazing Sealant on Lexan deck hatches. Cannot vouch for longevity yet - came as a recommendation from another sailor.

[Popcorn]

Try grinding the edge at a 45 degree angle, thus making the surface greater for the laminate to engage, and even possibly making the surface you are attaching it to join at the longest edge, encapsulating the compound inside the 45 degree area. To do this, fill the surface of the frame first with excess, then pressure the laminate into the frame squeezing the compound and its excess out, removing the excess with a knife or edge.
At least the compound will be contained in the frame and laminate not exposed to the elements, extending its life also. Of course a chrome or wood exterior frame could help and keep the laminate in place, but add to the cost.

[sailr69]

Originally Posted by SV__Grace

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.

right on bud. Butyl is the only sealant to use. there is a reason all automotive windows that are fixed use butyl. any caulk is bad because it is applied unevenly and then squeezed out when tightened. Butyl comes in a tape or rope section. easy to apply never gets hard and never leaks, ( period )

[wingssail]

Originally Posted by sailr69

right on bud. Butyl is the only sealant to use. there is a reason all automotive windows that are fixed use butyl. any caulk is bad because it is applied unevenly and then squeezed out when tightened. Butyl comes in a tape or rope section. easy to apply never gets hard and never leaks, ( period )

On our boat we used butyl tape on a skylight (cockpit floor) and on a hot day in Mexico it ran like black paint and dropped into our cabin.

[Patrigo]

T Rex, made by Soudal, a Belgian product is, I have found, unbeatable as a sealant /adhesive. Underwater, instant grip, etc., etc. Look it up, give it a go.

[Uncle Bob]

Originally Posted by Patrigo

T Rex, made by Soudal, a Belgian product is, I have found, unbeatable as a sealant /adhesive. Underwater, instant grip, etc., etc. Look it up, give it a go.

And I have found that it is not UV stable and degrades with time!
I have found Bostik/Simpsons to be a far better product.

[sailr69]

Originally Posted by wingssail

On our boat we used butyl tape on a skylight (cockpit floor) and on a hot day in Mexico it ran like black paint and dropped into our cabin.

what?? is that happening on cars too in Mexico?

[CaptainMarkS]

I'm in the process of doing exactly the same. What some folks missed is you requested a product for polycarbonate (Dow 795 is for glass). I ended up with a shortlist between:
Sikaflex 295-UV, Boatlife LifeSeal, 3M FastCure 4000 UV, and Bostik 940A.

Chotu, what did you end up choosing and how did it fare?

[Chotu]

Originally Posted by Mark Selawry

I'm in the process of doing exactly the same. What some folks missed is you requested a product for polycarbonate (Dow 795 is for glass). I ended up with a shortlist between:
Sikaflex 295-UV, Boatlife LifeSeal, 3M FastCure 4000 UV, and Bostik 940A.

Chotu, what did you end up choosing and how did it fare?

Sorry for the delay.

After all the debating, looking into different glass, adhesives, sealants, etc...

I went back to the lightest, strongest and most problematic material. Polycarbonate.

I got the real stuff this time and (stolen idea from the glazier who was too busy to do the project ), am going to use frames. He wouldn’t guarantee a mount without frames.

So I have some pretty big anodize J cap or J channel to allow an enormous bonding surface to come in contact with the boat and allow for a very large expansion slot to let the windows float in. I’m not sealing them at all, unless it gets too drafty.

The J cap, all the way around the windows, bonded to the hull, will keep all water out anyway. I’ll drop a sealant over the top J cap at the point it joins the hull for added protection.

Water will (as it always did with my crappy wooden U caps), just flow over the top cap, onto the polycarbonate and down to the deck, off the boat. It always worked before. I guess the internet just got the best of me making me want to try these sealant only windows. No more.

I don’t anticipate any problems as I never did have any problems until the old wood/epoxy U caps rotted away.

There is 1/2” room for expansion/contraction and I can use full, 4x8 sheets of real Lexan (Sabic UV protected, 10 year warranty) which eliminates the seam, so no need to caulk that either.

Putting them on next cold snap so it’s not so brutal on the roof.