Very Flexible Sealant (not adhesive) For Polycarbonate?

[CassidyNZ]

Originally Posted by Chotu

Here we go!!!

Updating the thread with findings.

Dow 795 elongation to break is 400%.
A random Sika WS-305AM product I just looked at elongation 750%!!

So on the half inch joint in your picture, if this spec is to be believed, the joint can elongate to 2” before failure should be expected? Or in the case of Sika, over 3”? Wow, your failure is then surely an anomaly.

Getting back to silicone. It was originally developed by Dow not as a sealant but as an adhesive. Whether or not it is compatible as an adhesive with plexiglass is another issue but I know that my daughter has immense tropical fish tanks with upwards of 1000 litres of water in them and the glass panels (10mm laminated) are held together on the corners by a thin bead of silicone. If applied correctly and left to cure, this stuff is very strong indeed. And even more intriguing is that to disassemble a tank takes very little effort.

I would also surmise that a half-inch joint may be structurally inappropriate and reducing size of the in-fill prior to sealing may be a solution.

[Sylph VI]

So I am wondering why not just use a UV resistant silicone sealant such as used in roofs and gutters?

[capnkev]

My understanding was that the 795 goes behind the window and then a UV rated sealant goes on the outside. I used 3M 4000UV. It’s been in FL for a year and looks perfect. That’s my 2 cents

[mike d.]

Hi ! So I had the problem of my poly carbonate lens letting go of silicone sealant on the edges in my painted aluminum frames ! Then I read about 795 ! Ok great ! Well I thought there must be a primer, so I called Dow and talked to a Techy there ! He said I should use Dow Corning 1200 os primer ! I did, and it works ! It works so well, I tried it with silicone sealant on a scrap piece, 1 section primed 1 section not ! I put on the silicone, let it cure for about a week ! When I tried to pull off the silicone on the primed edge I tore the sealant itself ! The non primed pulled away from the edge ! I used the primer to do the edge of the hatch edge and the 795, it hasn't budged !

[ThoFre97]

Originally Posted by Chotu

Here we go!!! ...

I’m off to search for the sealants with highest elongation that are compatible with polycarbonate

Finally on the right path, Take it from an engineer who had to study stress strain and elongation.

[ThoFre97]

Originally Posted by Supercat568

I own a glass shop. ...

Right, and good on you, but it ain’t glass! It’s polycarbonate and expands maybe 10 times as much. Take a look at this chart.

https://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

Hey Chotu, maybe you should try that Dow 795. They say it works great on glass. And hurry up because we’re running out of time.

[reiner]

Originally Posted by LakeSuperior

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.

Sikaflex is not the best produce to use on Perspex or plexiglass windows . They did develop a primer to improve the adhesion to poly plastics but people in the trade don’t use it for that

[rossdv8]

Originally Posted by NYSail

Never silicone

Geez, I just read this - I'd better apologise for the long post now!


I was told to never use silicone, and directed towards an exciting new product' called Sikaflex. So I tried it, and it worked great for keeping stainless fitting from corroding masts. But for sealing - not so well.


I started using silicone when I first started selling the stuff fairly early in its history in Australia. In the 40 or so years since I've used it for repairing almost everything, cars, boats, footwear..


When I discovered that the Main Roads Department was using it to stick stuff to Bitumen roads in our tropical heat, I looked closer and tried it for fitting Perspex (Plexiglass) windows to a wooden cabin. Since then every yacht I have bought has had all the leaks fixed with Silicone sealant, except for the few I tried using Sika on - and stripped and replaced with Silicone.


In my country we sell a brand name 'Selleys' and their product 'Selleys Wet Area Silicone Sealant' has been my go to product on yachts since it first appeared. I always have white cabins and decks, and despite black colours supposedly being the most durable in the tropics, I find that using White 'Wet Area Silicone' looks better (as I got older my hands got shakier).
Before the silicone 'goes off' it can be cleaned off Perspex easily with a vinegar soaked rag.

Silicone sealant that has set is notoriously hard to remove from fibreglass if it is used to seal fittings. I have heard that it can 'rot' stainless screws, but investigating that suggests they are damaged by the lack of air, rather than contact with silicone. Something to do with the chemical reaction between stainless steel (alloy mix) and the air providing a happy environment.


One neat thing about Wet Area Silicone Sealant is that it is designed for sealing bathrooms. Another neat thing about Silicone sealant is that most of those lovely big glass fish aquariums you see in restaurants and pubic places were held together by Silicone Sealant alone once it was available. Before the advent of Silicone Sealant they all had frames of metal angle around the edges of the glass. They might be held by other stuff now, but Silicone started it all I think.


I decided that something that can glue and seal 5 big panes of glass containing a massive weight of water that is trying to escape, will do me for sealing some windows and deck fittings.


My second last yacht had been a competitive racing boat before being retired to cruising. She was about 1/3 full of water when I saw and bought her. Most of it was fresh water, and as she had always been used in salt water, I suspected deck leaks. After repairing just about everything I discovered, in our first monsoon together, The front hatch glass and all cabin windows leaking.
Wet Area Silicone has a nice property in that if you smear some of the stuff on the perspex and fibreglass and aluminium around the leak, while it is leaking, until it is tacky, it is possible to keep doing this, very thin layer by layer until you build up a waterproof layer over the tacky bits to seal it temporarily until you can strip it back on a dry day.
Beats the hell out of a soggy berth in a storm.



I also used the stuff for temporary repairs to both glass and timber hulls, but it has to be cut out to a depth of about a millimeter before there's a chance that epoxy or polyester will adhere to it later - probably the reason shipwrights hate the stuff.


For cruising in various climates though it has two great attributes:
It sticks almost anything to almost anything and once cured, hangs on.
It remains flexible for most of its life,

although the Black seems most resistant to UV damage followed by White, then Clear. I always use White.



It does not hold paint well, BUT, if you let the stuff cure for a few weeks before painting it can be painted with reasonable success. Just needs touching up whenever it looks a bit ratty. This prolongs its life considerably too.

[Chotu]

Some fresh thoughts on how to reduce weight AND use glass.

I have a standard catamaran deckhouse with 4 sides.

A front set of windows, 2 side sets and a back with doors.

There is a LOT of window area because I need to see from the indoor helm.

Only the east side windows have failed. I figured out why. It’s at a dock right now which is putting more thermal issues into the east side. It goes from 60F to over 100F in a very short time each morning. The other side warms up as the air does. The east side rockets from 60 to 100+ from sunlight.

In any case, the front (nearly vertical windows) have no problems with 795 and staying put.

The aft windows don’t even see direct sunlight so they are completely fine.

It’s only the side windows that are a problem.

So why not use the right tools for the right job??

Do nothing to my front polycarbonate windows, replace with acrylic or polycarbonate a couple years down the road.

Use tinted glass for both side windows adding only about 100-140 extra pounds. Dow 795 these on using carefully designed joints followed the link Jedi sent to the user guide for 795. No thermal expansion and huge joint should make that a permanent fix.

Use polycarbonate for the aft windows and doors to keep weight down. They see no sun and have no problems. Just redoing the doors as I had temporary ones and am changing the door design. Use 795 or VHB for aft windows. Aft door ones are held by VHB alone now. Doing fine. Aft regular windows held on just fine with some silicone Gord once mentioned. Simple GE hardware store stuff.

[Celestialsailor]

Originally Posted by Cpt Mark

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

Islland Packet has relied on this for years.

Yup!...This is what I use on Polycarb. Little else wants to stick.

[JasonL]

Look for
Fixtech 200
Far superior performance than either Dow 795 or Sika 295
Does not require primers, surfaces do need to free of all old material.

It is used to install and fix very large poly and glass windows into ferries, tugs, ships.
Has greater stretch capability, but does require glazing to be supported/held in place while curing.

[rossdv8]

Looks like Silicone is still very popular for industrial use for bonding where high strength, long term durability and waterproof sealing ability is required.

[reiner]

Originally Posted by JasonL

Look for
Fixtech 200
Far superior performance than either Dow 795 or Sika 295
Does not require primers, surfaces do need to free of all old material.

It is used to install and fix very large poly and glass windows into ferries, tugs, ships.
Has greater stretch capability, but does require glazing to be supported/held in place while curing.

Yes Fixtech 200 is the best product on the market here in Australia. It does take some time to cure properly so no good for rush jobs but it sticks and seems pretty UV resistent . Not sure how available it is in the US or Europe

[Celestialsailor]

Originally Posted by 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

Originally Posted by Chotu

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

I know right?...I think a lot here are mistaking success with Dow 795 on Acrylic (Plexi-Glass) instead of Poly carbonate. Sil Pruf works on Polycarb. A little messy to work with.

[DomPerignon]

I have been in roofing all my life and from my experience the best recipe for a waterproof, sunproof , freezeproof, anything you like proof , is 100% silicone. And I mean only 100 % pure silicone. Often times it will read silicone on the tube but it’s not 100% silicone.