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  #11  
Old 12-04-2013
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Re: Proper adhesive/sealer for Lexan

Quote:
Originally Posted by Adele-H View Post
I had redone my hatch with 5200 last year, it leaks after just one season, when I step on the lexan, I can see where it is no longer bonding to the lexan.
Definetly will be redoing the hatch in the spring and trying out the 795.
Though the experience wasn't a total loss, I did manage to learn how to handle a lot of goopy stuff and not get it all over the place.
Essentially, I taped up the lexan everywhere the 'glue wasn't supposed to be and taped up the alluminum frame ....everywhere the "glue " wasn't supposed to bond to.
Put a lot of goop on the frame, pushed the glass down, clean all the stuff that oozed out on top, went down below and cleaned up all the stuuf down there, waited maybe an hour or so and started peeling of the tape below, first the frame, then the glass.
Came out clean, looks professional, but using the wrong stuff, it leaks now.
Still, it was good all season the lexan I can save, the frame I'll clean and do it all again in the spring.
There are really very few uses for 5200 on a boat. Perhaps below the waterline, but anything you ever think might need to be resealed, or removed by you or a future owner do not use 5200 on it! It is the worst stuff on the planet to get off. They should make you sign a release form before buying the stuff! When reading the book Breaking Seas, he talked about trying to stop leaks with 5200 with lots of tubes of the stuff, if there was ever a wrong product for the job that is it.
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Old 12-04-2013
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Re: Proper adhesive/sealer for Lexan

Someone was once quoted that "...you should have to have a license to use 5200 or silicone on a boat."

I agree, Dow 795 (which is a very different silicone from most) being the exception for ports and hatch lenses.
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Old 12-04-2013
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Re: Proper adhesive/sealer for Lexan

I posted this in a similar thread but it bears repeating here. If you need a lot, 700 is much less expensive than 795. As I understand it, 732 is basically 700 without the military approvals. Edit: I said that backwards - 700 is basically 732 without the military approvals.

Quote:
Originally Posted by Geoff54 View Post
I don't know if this is any interest but I will soon be replacing fixed ports on an S2 11.0 which were installed with Dow Corning 700 32 years ago and are still leak free. There are no mechanical fastenings.

I don't know how it compares to 795 but acording to Dow, 700 is an industrial silicone used for adhering auto trim, appliance trim and nameplates, creating formed-in-place gaskets for compressors, gear boxes and pumps, bonding appliance parts and signs and caulking doors and windows for sealing out moisture.

From S2 Sailboats History and Referral Information:

The windows were made from bronze tinted Lexan…..

....The sealant used is Dow 700 industrial grade silicone caulk; this is available in a few different colors (equivalent brands are more than likely available in your area).

Here is how we installed the window's originally. We took a plexi window with the outer surface covered entirely in masking tape, and set it temporarily in its opening. Next we shimmed it (only if necessary) to ensure it would be flush with the surrounding fiberglass. We masked off the surrounding border of the opening and drew "cross hairs" on the masking tape (both on the window and the surrounding mask) to aid in alignment while installing the window with sealant. The perimeter of the window's surface (that comes in contact with the opening) was then roughed up with 80 grit sandpaper. Take care not to scratch any portion of the window that you will be looking through. With the window removed, both the opening perimeter and the edges of the window received a generous bead of black silicone caulk. Here comes the Chinese fire drill; the window was literally mushed in place from the outside, while someone inside the boat armed with a putty knife and lot of rags, caught the oozing caulk and wiped it on rags.

From the outside, once the window was in flush with its surroundings and aligned with the cross hairs, a plastic scraper was used to scrape all the outer ooze off flush with the window and cabin house. The caulk was then allowed to cure for twenty-four hours. The thicker the bead of silicone, the longer it needs to cure, and it will take a while before the entire seal is cured all the way through. The masking tape wasn't pulled off until after the twenty-four hours elapsed.

If you just need to make your seal look pretty again, dig out the outer layer of sealant. Mask off, overfill with silicone and level with a plastic scraper. Now, the people that did this on regular basis did not really need to touch up the caulk much to make it look pretty. Nevertheless, if it does need to be touched up, here is what you do. You will need a small container of water, more rags, and more black silicone.

Apply the silicone where you need it and then dip your finger in the water, smooth the caulk, wipe your finger on a rag. Re-wet your finger, smooth seam, wipe finger on rag, repeat as necessary. You may elect to do this step while the masking is all still in place.

Things to Remember:

#1. If you skimp on the caulk, you will end up with either air bubbles, voids in the seal or both.
#2. Silicone does not stick unless all the surfaces are clean and dry.
#3. Don't let someone talk you into using something other than silicone. The thermal expansion and contraction rates are drastically different between the Plexiglas and the fiberglass. So elasticity of the cured sealant is critical.
#4. Your elastomeric poly-sulfides are better adhesives (remember cleanliness when using silicone). But, they cure hard and cannot expand and contract with the changes in temperature.
#5. Keep solvents away from Plexiglas, Lexan, and acrylics. They will craze Plexiglas and speed its degradation. Even Windex has NO PLACE on or near these polycarbonate materials. For general cleaning, furniture polish like Pledge is your best bet. For more serious cleaning use denatured alcohol.
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Last edited by Geoff54; 12-04-2013 at 10:59 PM.
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Re: Proper adhesive/sealer for Lexan

I believe there is a Dow 739 as well. All are structural silicone, much different from the bathtub caulk at the hardware store. One of their uses is adhering glazing to buildings without fasteners.
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Old 12-05-2013
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Re: Proper adhesive/sealer for Lexan

i need help guys...and I dont want ot order sealants from the states

Im about to do my portlights, they are the flush sealed type

they have a gasket(rubber) and had what seems to be butyl tape AND screws dammit

we do not have ANY of the sealants mentioned except for 5200

we have MANY window and construction type sealants...my best guess was one made by dap or similar

it was water based very felixible and stayed soft unlike 5200

would this be a good sealant to try out?

what other brands names that home depot or similar carry that I could search for down here?

thanks
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Re: Proper adhesive/sealer for Lexan

Generally Home Depot and equivalents DO NOT routinely carry the 'good stuff'.. I had to get my DC795 from a cladding and insulation wholesaler. I'd be surprised if there was not a distributor in your region.. have you tried going to the Dow Corning website? (ignore the 'implant fill option' page )
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Re: Proper adhesive/sealer for Lexan

yeah I need to find a distributor or something...we have boat life too but the small tube costs $34!

so I was even thinking about using simple neoprene gasket and no sealant...

we just did our toerails and we did use 5200 as strength is good there...but not for portlights...I dont like 5200 for most non structural things...

anybody else have ideas? sorry for the hijack op!

should I be looking for water based or oil

polysulfides or not

we have sikaflex but not UV

that work ok?

thanks
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Old 12-05-2013
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Re: Proper adhesive/sealer for Lexan

Quote:
Originally Posted by Adele-H View Post
I had redone my hatch with 5200 last year, it leaks after just one season, when I step on the lexan, I can see where it is no longer bonding to the lexan.
This is most likely because your hatch was never designed for polycarbonate and was designed for CAST ACRYLIC. Polyuretahnes & polysulfides can leach the plasticizers out of polycarb and cast acrylic and are contraindicated with most hatch lenses. Sika 295UV is one of the only PU's designed for hatch lenses but you need to also use the special primer.



Quote:
Originally Posted by Adele-H View Post
Definetly will be redoing the hatch in the spring and trying out the 795.
Though the experience wasn't a total loss, I did manage to learn how to handle a lot of goopy stuff and not get it all over the place.
The secret with sealing hatches is to get it CLEAN, CLEAN, CLEAN and allow the proper cure time. You also need to use the proper material, most often cast acrylic, and then Dow 795 or similar BUT it must have adequate film thickness, you need shims when curing, or it will still fail.


Quote:
Originally Posted by Adele-H View Post
Essentially, I taped up the lexan everywhere the 'glue wasn't supposed to be and taped up the alluminum frame ....everywhere the "glue " wasn't supposed to bond to.

Unless your hatch has "cross bars" to support the Lexan it was NOT designed for Lexan and was designed for cast acrylic.

Lexan foreshortens/flexes when stepped on thus breaking the seal. More than one owner has landed in a cabin due to using the WRONG material in a hatch lens replacement.

Lexan/polycarbonate is pretty much shatter proof but flexes a LOT more easily. Cast acrylic flexes less, and can be cracked, but holds up in UV a lot better. The vast majority of plastic ports and hatches are made of cast acrylic not polycarbonate. Only some Bomar's are made from Lexan and they have cross bars under the glass.
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Last edited by Maine Sail; 12-05-2013 at 11:59 AM.
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Old 12-05-2013
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Re: Proper adhesive/sealer for Lexan

Quote:
Originally Posted by christian.hess View Post
yeah I need to find a distributor or something...we have boat life too but the small tube costs $34!

so I was even thinking about using simple neoprene gasket and no sealant...

we just did our toerails and we did use 5200 as strength is good there...but not for portlights...I dont like 5200 for most non structural things...

anybody else have ideas? sorry for the hijack op!

should I be looking for water based or oil

polysulfides or not

we have sikaflex but not UV


thanks
Dow 795. McMaster has it.
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Re: Proper adhesive/sealer for Lexan

Last winter, I rebuilt 45-year-old portlights using Dow 795 to secure the new plexiglass in the U-channel aluminum frames. After a 2-week cure, I used butyl tape bedding and rivets to secure the portlight assemblies back into their original cutouts. No leaks yet.

Dow 795 and butyl tape are both easy to work with and highly recommended.
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