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Old 16-04-2016, 04:12   #1
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Portlight sealing

Any recommendations on the best sealant for portlights?
Fiberglass hull, lexan, and bronze housings.

Thinking of Sika 295 white (the sealer not the black adhisive) plus the 226 cleaner but want to do it right the first time
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Old 16-04-2016, 05:59   #2
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Re: Portlight sealing

If you are speaking the frames to hull, butyl tape (compass marine bed-it) For the lights, 795 Dow Corning is highly recommended on this forum with a 3m VHB tape if necessary. I like Sikaflex products, however for some portlight/hatch lens installs they want you to use a primer that is $$$. I used Ultraglaze 4000 last time...not entirely satisfied...will go with 795 on the next lens replacement.


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Old 16-04-2016, 06:17   #3
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Re: Portlight sealing

Second the recommendations from Capt Cook.

I have redone almost all the ports on my boat. For bedding the port to the boat butyl tape is the way to go. Be aware that all butyl tape is NOT created equal. Safest bet is to buy directly from Compass Marine. ***Buy Bed-It Butyl Tape*** Photo Gallery by Compass Marine How To at pbase.com

I installed new plexiglass in several of the ports and used Dow 795. The stuff is really, really messy but end result is worth it. Just tape all the edges, cover everything and wear gloves.
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Old 16-04-2016, 09:57   #4
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Re: Portlight sealing

I'm a big fan of butyl tape and use it for a variety of sealing jobs. I am not an expert on sealing portlights to hulls but I remember there were at least one long one thread on the forum, and I think a few more, on this exact issue. From what I remember (barely) is that there was a strong recommendation on some more permanent special sealers, not butyl tape. You might want to do a good search for that just to get some other views. For all I know butyl tape might be fine but it seems like it might not have all the characteristics best for this type of application
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Old 16-04-2016, 10:10   #5
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Re: Portlight sealing

We used butyl tape from compass marine specifically because it's not permanent. It's very very sticky so It almost forms a permanent seal anyhow - like glue that never dries... Heck it's what is used on windshields.

A little goes a long way. A mistake we have made again and again is to use too much butyl. It takes forever to compress and you end up wasting the stuff that squishes out.

Wherever we have used butyl we have never experienced a leak again.

I used life-calk on the portlights when we replaced them. Easy to clean up with acetone after application but it stains bronze.


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Old 16-04-2016, 10:17   #6
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Re: Portlight sealing

I'm most pleased with adhesion by 3M VHB 4991 2.3mm thickness and with the sealant as Dow 791 due to it's expansion coefficient.
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Old 16-04-2016, 15:04   #7
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Re: Portlight sealing

If it makes any difference, I am now thinking to epoxy powder coat the bronze frames to brighten it up outside

Rather than external frame, all that is viable from the outside is the lexan, with a bead of caulk. The frame is internal, and until I disassemble it I am not sure how it all connects.

3 different materials, lexan, fiberglass, and epoxy coated bronze
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Old 16-04-2016, 16:06   #8
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Re: Portlight sealing

Quote:
Originally Posted by Hoghead View Post
.............. I am now thinking to epoxy powder coat the bronze frames to brighten it up outside .... The frame is internal
...................
I'm confused. "frames to brighten it up outside", but "frame is internal"?

If it's relevant, I would submit that the 3M VHB 4991 tape adhering the polycarbonate to the fiberglass and the Dow 791 sealant produces a good finish without frames or fasteners.

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Old 16-04-2016, 17:35   #9
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Re: Portlight sealing

[QUOTE=Hudson Force;2098804]I'm confused. "frames to brighten it up outside", but "frame is internal"


Typo frame is internal
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