# Proper adhesive/sealer for Lexan



## RoadTool (Nov 25, 2004)

Im seriously considering replacing my ports with fixed lexan sheet , and I need to know the proper adhesive/sealer , I read that 4200/5200 , Boatlife is not advised .


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## DelmarRey (Aug 25, 2001)

The best sealer I''ve found for lexan IS THE boatLIFE--- Life Seal Sealant #1170. The stuff is real messy, but that''s what makes it stick so good. If you can manage to work it in without touching it with your fingers it''ll come out great. Even if you use rubber gloves, The stuff doesn''t want to come off of the gloves and gets everywhere. Once it cures it stays fairly soft, exactly what you want for a flexing hull/deck.
It works good on teak too....................._/)


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## RoadTool (Nov 25, 2004)

But is Life Caulk another polysulfide thats not recommended for plastics/lexan?


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## DelmarRey (Aug 25, 2001)

Corrected my first post NO on the Life Seal Sealant!


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## Silmaril (Feb 22, 2003)

The best product I have found for Lexan type lenses/windows is Dow Corning 795 construction adhesive.

The caveats are that it takes 7 days to set up... don''t be in a hurry, make sure you prep well, follow the instructions, clean up immediately.

This is what the "Pro''s" use when re-glazing ports, hatches, cabin lights.


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## Adele-H (Nov 18, 2012)

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.


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## jrd22 (Nov 14, 2000)

I second the 795, re-did the pilothouse windows in our boat (Lexan) a couple of years ago, no leaks at all (PNW). I sanded the Lexan in the areas that were going to be covered/sealed in order to give the sealant something to "grab". Faster (Ron) here on SN recommended the DC 795 and I'm glad he did, good stuff.


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## StormBay (Sep 30, 2010)

Third vote for 795. Used it on our last boat and never had a problem.


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## PaulinVictoria (Aug 23, 2009)

I bought some to use on my last boat, then sold it before I got a chance to. Seemed like the best option to me


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## mitiempo (Sep 19, 2008)

Dow 795, GE SG-4000, or Sika Flex 295 UV with primer are the best choices. 
The details are here: Which Sealants To Use
Select Plastics is the largest marine hatch repair facility in the world.

Adele
Lexan is not the best choice for a hatch unless it was lexan originally. Only Bomar hatches with the metal cross beams use lexan. Every other hatch manufacturer - Lewmar, Bomar, etc all use cast acrylic for the very reason you found. Lexan deflects when stepped on and the seal will break - regardless of sealant type. Cast acrylic is also much more scratch resistant and will last years without crazing, lexan crazes in a few years.

Roadtool
If you have not yet purchased the lexan use cast acrylic (plexiglass) instead for the reasons above. Lots of good information at the link posted.


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## miatapaul (Dec 15, 2006)

Adele-H said:


> 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.
> ...


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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## mitiempo (Sep 19, 2008)

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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## Geoff54 (Oct 30, 2011)

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. *



Geoff54 said:


> 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.
> 
> ...


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## mitiempo (Sep 19, 2008)

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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## christian.hess (Sep 18, 2013)

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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## Faster (Sep 13, 2005)

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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## christian.hess (Sep 18, 2013)

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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## Maine Sail (Jan 6, 2003)

Adele-H said:


> 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.



Adele-H said:


> 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.



Adele-H said:


> 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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## overbored (Oct 8, 2010)

christian.hess said:


> 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...
> 
> ...


Dow 795. McMaster has it.
McMaster-Carr


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## hriehl1 (Aug 8, 2007)

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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## christian.hess (Sep 18, 2013)

overbored said:


> Dow 795. McMaster has it.
> McMaster-Carr


yeah thanks I know, issue is I dont cant import certain things down to el salvador...

one tube of sealant ends up costing $100, and I have to wait 3 weeks...

hence my questions on alternate sealants if anybody had experience with...

I mean I could use 5200 but I dont want to mess with them in 6 months to a year

anybdoy use only manual methods to seal?


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## christian.hess (Sep 18, 2013)

hriehl1 said:


> 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.


did it matter what color butyl tape you used? I have seen the black stuff at the hardware store

maybe just this and the rubber original gasket?

thanks


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## sulli (Mar 9, 2013)

I would definitely not use the Dow 795 I have 35 years in the residential window business I used it in the past, very weak adhesive link between glass and vinyl and its SILICONE. I dont like silicone on a boat, too difficult to remove the residue when it fails. I have used products similar to this 


> PRODUCT: CLEAR, SEALANT. SOLVENT-FREE 100% SOLIDS POLYESTHER ADHESIVE, CLEAR COLOR, 10.1 OZ TUBES. 24 TUBES/CASE. PRICE/CASE.
> 
> DESCRIPTION: Chem Link CLEAR is a high quality moisture curing elastomeric sealant formulated with polyether technology for use in virtually any high visibility sealing application.
> 
> ...


I have no affiliation with these folks, the company I dealt with went out of business and the product I used was packed under their label, this seems to be the same type.


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## mitiempo (Sep 19, 2008)

I would stick to the three sealants recommended by Tony at Select plastics. 

GE SG-4000, Sika Flex 295UV with primer or Dow 795. Anything else is an experiment and who wants to re-do this in a year?

sulli

It says "showers (non ponding areas)" I take that to mean it cannot sit with water on it. Doesn't sound good for a boat if that is true.


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## DonScribner (Jan 9, 2011)

As has been said already, plasticizer migration is a serious problem when sealing plastics. DO NOT use a polyurethane based sealant on any plastic, polycarbonate, acrylic, copoly. Stay with the silicone based STRUCTURAL sealants. 795 was reformulated a few years back and is now considered structural but 995 is better. As far as polycarbonate in the sun . . . my company has been supplying it for 30 years. We are a skylight manufacturer. Draw your own conclusions. We moved from cast acrylic (which we invented) because polycarbonate is more impact resistant, ie, more flexible. We now supply impact modified acrylic in lieu poly and have moved to a cheaper material (copolyester) for commercial applications. 

The best way to install any plastic with silicone is to adhere the material with structural glazing tape, 3/16" min and about 1/4" from the edge. Mask the surface of the glazing and the perimeter of the mounting area leaving a 1/4" gape around the perimeter. This adheres the glazing and supplies the space that others have suggested by shims. Inject the silicone under the glazing and apply a bead completely around it. Now comes the REAL IMPORTANT part: tool your joint. I use tooling spray and a plastic spoon for a joint that looks like a perfect rubber gasket. If you don't tool the joint, it isn't complete or watertight. Water will find it's way in. Sealant manufactures won't warranty their products if the joints aren't tooled. And don't believe any testosterone fueled boasts about never needing to tool. I will stand on, "If they say that, they don't know what they're talking about."


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## Geoff54 (Oct 30, 2011)

christian.hess said:


> 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
> 
> ...


I have a little material cheat sheet - sorry I won't share it because I assembled it over time from multiple sources, some unverified, therefore double check this information if you want to use it.

The most flexible non silicone on my list is 3M 4000UV (Polyurethane) with an elongation at break of > 700% - much greater than 4200, 5200 or most industrial silicones. I believe this is what Morris uses for deck hardware. It's 3M so if you can get 5200 maybe you can get 4000.


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## Geoff54 (Oct 30, 2011)

Maine Sail said:


> 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.


My hatches are of unsupported polycarbonate and they flex very little. But they are 3/4" thick


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## mitiempo (Sep 19, 2008)

Geoff54 said:


> My hatches are of unsupported polycarbonate and they flex very little. But they are 3/4" thick


What brand of hatch? Or did you replace the lens yourself?


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## Geoff54 (Oct 30, 2011)

DonScribner said:


> 795 was reformulated a few years back and is now considered structural but 995 is better.


This sounds very good. Elongation is 525% and the price is reasonable.

"Dow Corning® 995 Silicone Structural Sealant is a one-component, self-priming, shelf-stable, neutral-cure, elastomeric adhesive specifically formulated for silicone structural glazing and exhibits excellent unprimed adhesion to most building substrates. This product has superior unprimed adhesion for structural glazing applications for hurricane or impact rated windows and doors. It has a movement capability of +/- 50%."


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## Geoff54 (Oct 30, 2011)

mitiempo said:


> What brand of hatch? Or did you replace the lens yourself?


On most boats, S2 molded the "Frame" as part of the cabin top and then used either 1/2" or 3/4" lexan cut from flat stock for the hatch. The lexan was drilled and tapped so that hinges and latches could be attached directly.


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## christian.hess (Sep 18, 2013)

Geoff54 said:


> I have a little material cheat sheet - sorry I won't share it because I assembled it over time from multiple sources, some unverified, therefore double check this information if you want to use it.
> 
> The most flexible non silicone on my list is 3M 4000UV (Polyurethane) with an elongation at break of > 700% - much greater than 4200, 5200 or most industrial silicones. I believe this is what Morris uses for deck hardware. It's 3M so if you can get 5200 maybe you can get 4000.


yeah I think 3m is a safe bet...Ill search! and thanks so much!

man is it tough sometimes down here


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## miatapaul (Dec 15, 2006)

christian.hess said:


> yeah thanks I know, issue is I dont cant import certain things down to el salvador...
> 
> one tube of sealant ends up costing $100, and I have to wait 3 weeks...
> 
> ...





christian.hess said:


> yeah I think 3m is a safe bet...Ill search! and thanks so much!
> 
> man is it tough sometimes down here


If you can find a good real commercial supply center, they likely have the right stuff. You want true structural silicone. So if you can find someone who does replacement windows in high rise buildings then they might be able to help. There could be a local product that works well and might even be relabeled version of one of these. 3M products generally are good though, just not 5200.


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## Geoff54 (Oct 30, 2011)

I went to the Dow Corning website, did a search for El Salvador and it returned the regional sales office in Mexico. It might be worth a call to see if there is a retailer for near you where you could get one of the industrial silicones.	

For purchasing information, please contact this Dow Corning regional sales office directly.

Dow Corning de México S.A. de C.V. 
Direct Dial: 55 19 3887 9109

DOW CORNING DE MÉXICO S.A. DE C.V. 
BLVD MANUEL ÁVILA CAMACHO 138 
PISO2
COL. LOMAS DE CHAPULTEPEC 
DEL. MIGUEL HIDALGO 
11000 MÉXICO, 
DISTRITO FEDERAL 
MEXICO


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## socal c25 (Nov 1, 2013)

I used the 3M 4000 on my lexan portlights and it work good with no problems, just make sure to follow instructions and everything has got to be clean... really clean.


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