Help! What Sealant is Better than Dow 795 for polycarbonate??

[Chotu]

Originally Posted by Mike Banks

Well, I only used heavy glass for mine--but that was held in place using a rubber strip, and there was a series of captive bolts welded to the inside of a cover gasket face that went through the cabin walls and a reinforcing plate, and the whole lot was bolted together sandwiching the glass as though it were in the jaws of a vice with rubber on each jaw. It never leaked.

Some trawler men I knew used polycarbonate and they used it glued into a metal frame--I think they used a product made by Sikoflex. It was really powerful stuff. One aapplies one layer to the frame, inserts ythe window material, puts another coat on the windoe w in its frame, adds the cover stripo, and the wholele is tightened down lightly and the job cleaned up. Later after the compound has set, the nuts are tightened again, but not overtightened.

Apparently the trick is to keep as much of the compound as possible both sides of the glass, yet have the glass evenly secured all around. The thickness of the rubbery set compound is what allows for small movements.

Yes. This is the ideal way to do it. Unfortunately no frame or rebate here which is the issue.

[slug]

Originally Posted by mdenize

Hi Chotu

Glued on windows can be a real pain but I can share my experience which is with an Ali boat that only had glued on windows (no other fixings)

My Mclay has glass windscreens and tinted poly side windows and hatch glazing.

All are installed the same way which is mostly very successful (except in extreme storm conditions when the boat flexes just too much for the curved windows which I bolted as well to retain the curves.

The system they use is an etch primer on the window and the boat (3m I think) which as well as prepping the surface stops UV getting to the sealant,

followed by a Black double sided sticky foam packer tape (at least 6mm thick maybe 8 and about 10mm Wide). This locates the window and stops the sealant squeezing through to the inside so it looks really neat but the main function is so the sealant has real thickness and give it lots of time to cure.

Then the product that does the sealing is a black windscreen sealant ( I think 3m) that sticks like Sh#$ to blanket, The way to avoid a mess like you seem to have is to mask the window and boat (wide tape about 5mm away from the outline of the window to allow a nice cove then go to town with the sealant gun and wipe away the excess with a wet plastic coated finger, you end up with a nice cove that sheds water very well. Frankly it is hard to believe it will keep a 1m2 window installed in 80 Knots but it does!

If you want the exact product detail I can try to find out for you.

Hope this helps at least a bit!

Yah..you have described the classic installation

The foam tape that keep the adhesive from squeezing out on the inside is important

Also remember that you need perimeter spacers to overcome gravity and keep the window centered in its frame

[Chotu]

Originally Posted by mdenize

Hi Chotu

Glued on windows can be a real pain but I can share my experience which is with an Ali boat that only had glued on windows (no other fixings)

My Mclay has glass windscreens and tinted poly side windows and hatch glazing.

All are installed the same way which is mostly very successful (except in extreme storm conditions when the boat flexes just too much for the curved windows which I bolted as well to retain the curves.

The system they use is an etch primer on the window and the boat (3m I think) which as well as prepping the surface stops UV getting to the sealant,

followed by a Black double sided sticky foam packer tape (at least 6mm thick maybe 8 and about 10mm Wide). This locates the window and stops the sealant squeezing through to the inside so it looks really neat but the main function is so the sealant has real thickness and give it lots of time to cure.

Then the product that does the sealing is a black windscreen sealant ( I think 3m) that sticks like Sh#$ to blanket, The way to avoid a mess like you seem to have is to mask the window and boat (wide tape about 5mm away from the outline of the window to allow a nice cove then go to town with the sealant gun and wipe away the excess with a wet plastic coated finger, you end up with a nice cove that sheds water very well. Frankly it is hard to believe it will keep a 1m2 window installed in 80 Knots but it does!

If you want the exact product detail I can try to find out for you.

Hope this helps at least a bit!

Couldn't hurt. What's the product just to be sure?


Although I have to admit I'm leaning very heavily toward flashing tape. There is an infomercial looking one that I tried in one of my test patches that's looking good and holding like crazy to the hull and to the polycarbonate.This completely seals the window off from rain and also from water going "up" from your other post. Ha ha

I'm just cutting it to the size of the black area on the hull in my pics and letting it overlap onto the polycarbonate by 3/4 of an inch.

It doesn't look as nice as a good caulking cove bead. That bothers me a bit, but it's not bad. Girlfriend says I'm crazy to think it doesn't look good. I see tape. She says it blends in completely.

But it works like crazy because it's a physical barrier to the water without any possibility of near term failure.

[Chotu]

Originally Posted by MJH

Sounds like a faulty design or misuse of poly carbonate for that large a window. I question the practicality of them offshore in a rough seas impact...I've seen some online photos of boats losing them...then again maybe you are not going offshore, you didn't share your plan.

My neighbor had a large fiberglass dodger built for his center cockpit Spencer 1300 (44') with the three piece windscreen made of tinted auto windshield glass; the dodger covered the entire cockpit. I always thought that was a great design as the windows never leaked, faded or cracked and cleaned up so much nicer than poly carbonate.

~ ~ _/) ~ ~ MJH

How would they blow out and get lost? They're bullet resistant.

[Chotu]

This is the stuff that I am ending up using.

Keeping in mind the VHB tape is what holds the windows in place, and that is already there, I just have to get the water from the roof onto the face of the polycarbonate. From the face, it just drains overboard. No issues.

So instead of experimenting around with all different types of glazing compound and having many failures, I’m just going to divert the water from the roof to the face of the Poly carbonate. The stuff sticks like crazy to poly carbonate and the hull, so it should be good.

I don’t know how long this stuff is going to last out in the hot sun, but I guess time will tell. The cheap infomercial label puts me off, but the product inside seems OK. I guess we will see how long it holds up.

[Sparx]

I have used this flex tape for out in the sun applications with good results. I keep some on board for repairs. Makes good chafe protection on a dinghy.

[warrior 90]

Originally Posted by Chotu

Couldn't hurt. What's the product just to be sure?


Although I have to admit I'm leaning very heavily toward flashing tape. There is an infomercial looking one that I tried in one of my test patches that's looking good and holding like crazy to the hull and to the polycarbonate.This completely seals the window off from rain and also from water going "up" from your other post. Ha ha

I'm just cutting it to the size of the black area on the hull in my pics and letting it overlap onto the polycarbonate by 3/4 of an inch.

It doesn't look as nice as a good caulking cove bead. That bothers me a bit, but it's not bad. Girlfriend says I'm crazy to think it doesn't look good. I see tape. She says it blends in completely.

But it works like crazy because it's a physical barrier to the water without any possibility of near term failure.

Not an expert on the topic but I like the idea of flashing. If it leaks it´s easy to replace and without removing the window....or did I miss something ?

[Chotu]

Originally Posted by Sparx

I have used this flex tape for out in the sun applications with good results. I keep some on board for repairs. Makes good chafe protection on a dinghy.

Thanks!! That's encouraging.

[Chotu]

Originally Posted by warrior 90

Not an expert on the topic but I like the idea of flashing. If it leaks it´s easy to replace and without removing the window....or did I miss something ?

I agree and am using it. 👍

[mdenize]

Originally Posted by Chotu

Couldn't hurt. What's the product just to be sure?

The system is Simson by Bostick.

The primer is Simson Prep M for non porous or Prep P for Porous if you want maximum strength as it acts as a key.

Then the Foam tape framing the inside of the window acts a constant thickness packer and method of holding the window while the sealant cures.

Then the sealant is Simson ISR 70-03 which has a elongation at break of 250% and a shear strength of 2.5Mpa (362psi) so no wonder my windows stay in there!

Here is the product sheet

https://adhesives.nz/media/96/simson-70-03-tds.pdf

Note the gap on my boat is about 6mm not the 2mm suggested recommendation, I thick the extra thickness allows a lot more flexibility of the the hull before the window is under any stress

The end result is a very good looking finish with no leaks and is quite replaceable if you are unlucky enough to break a window or more likely if the poly carb starts to craze up

[jhulmer]

Dow 795 has a strict expiration date. If you use it after that it will most likely not cure properly. I have switched to Dowsil 995 after watching this video. I just rehabed all my hatches and so far so good. BUT, I have yet to test it in the brutal sun and sea!

https://www.youtube.com/watch?v=g382Kzm9SjA&t=1232s

[wingssail]

Originally Posted by NYSail

Maybe try butyl tape....... great stuff. Not an adhesive but stays supple. Maybe use butyl tape then a sealant on top. Maine sails website sells the stuff.... great product.

We've experienced Butyl tape becoming runny and dripping down into the boat on really hot days.

[Chotu]

Updating... The Dow is cracked at the surface but is still soft which means it probably isn't cracked deeper in.

I'm going to hold off on the tape I planned to put over the cracked sealant until I see some sign it's leaking. Then I can put the tape on.

[Chotu]

Originally Posted by wingssail

We've experienced Butyl tape becoming runny and dripping down into the boat on really hot days.

I think there are do many butyl tapes out there we have different experiences. I use the readily available and cheap gray stuff in the plumbing section at Ace Hardware.

No leaks and no melted butyl tape.

It was used on all my cleats and other hull penetrations like thru hulls above the waterline.

My boat gets VERY hot (which is why there are window issues) and the butyl tape never disappoints.

Of course there are all sorts of different ones.

[Boatguy30]

I used clear Lexel available from most Ace hardwares. It will no doubt get a bit dirty over time, but not as bad as clear silicone. I also used it to fill some stretched stiching holes on my Bimini. Also use it exclusively in new sta Lok assemblies. Used to use the white, but seems to have been reformulated and the white dries very slowly now.