Sealant on bare aluminium?

[Newport41]

So after days of removing 4 different types of old sealant I'm ready to reseal the windows properly. Now I know there are a lot of threads out there touching on sealantand, and I've read them carefully,but I need conformation and a little specific advice as always. Were I'm sealing the glass (yes it is glass) to the aluminium frame I was going to use 5200 to seal it to the flange inside of the glass and then a good quality polysulfide to seal the glass to the outside flange. The polysulfide on the outside will be replacing the old gasket that has gone hard and for which there is no replacement available. Then I was going to use the polysulfide to seal the frame to the deck housing. Does that sound right? I'm also wondering if I need to paint the aluminuim with something first or can the sealant be applied to clean aluminium?
Thanks agian in advance.

[RickBowman]

I never use 3M 5200 unless I was to bond a deck to a hull. That stuff is designed to be permanent, not the best choice as a sealant that may have to come apart again in the future.

[sailingdog]

I wouldn't be using 5200 to put a port in place. You'll eventually have to remove these ports...and then you'll have a tough time. I would use 3M 4200 rather than 5200 for both sides of the glazing. You shouldn't need to coat or paint the aluminum at all. I would also use 4200 to bed the frame to the fiberglass.

Although you could use a polysulfide-based sealant, it will take far longer to fully cure than 4200, which fully cures in 24 hours IIRC. Polysulfides usually take five or more days to fully cure. For instance, BoatLife LifeCalk says it take 7-10 days to cure... hmm... which would you rather wait... one day or a week?, especially if there is no real advantage to the polysulfide sealant.

[Newport41]

I was thinking 4200 fast cure at first but I was worried about it's ability to adhere to glass. I was thinking of using the 5200 to hold the glass in place on the back side and then using something (probably the 4200 as suggested) on the front side as a replacable seal. If the 4200 will adhere to glass well then I will use it for everything except the plastic frame portholes up forward. Any thoughts?

[sailingdog]

It should bond pretty well to the glass and the aluminum, as well as the plastic frames. BTW, the polysulfide sealants will generally attack most plastics—including ABS, Plexiglass/Acrylic, and Polycarbonate—so I wouldn't recommend using them for the plastic portholes.

[Valiente]

Originally Posted by Newport41

I was thinking 4200 fast cure at first but I was worried about it's ability to adhere to glass. I was thinking of using the 5200 to hold the glass in place on the back side and then using something (probably the 4200 as suggested) on the front side as a replacable seal. If the 4200 will adhere to glass well then I will use it for everything except the plastic frame portholes up forward. Any thoughts?

Use the 4200 or Sikiflex 231 or even 291 and just take care with your gasketing, which is the main barrier in my opinion. I just redid my fixed portlights in my saloon last year in 1/4" Plexiglass (it's not a big deal to redo this job every 10 years when it "gets crazy") and I used clear silicone exterior caulk, because I use the "grey gasketing" so familiar to C&C owners.

I assume you are using some form of gasketing or whatever equals butyl tape in a saltwater setting...

[Sailormann]

I would definitely suggest you fashion some type of gasket out of neoprene or something else - particularly if you are using glass which is not likely to flex at all to any degree when you are dogging the hatches closed.

[sailingdog]

I like neoprene gaskets, but the only problem with them is that they have to be under compression, and a fair bit of it to work properly. A lot of ports and hatches don't supply the compression needed to make them work leak-free. THe ones I've seen that they work on quite well are the plexiglass or lexan ports that are through bolted, without a frame. This seems to be the way non-opening ports on many boats are going, since it is more secure and far less expensive to do as I understand it.

[Newport41]

Yeah, I was going to use the factory recommended silicon hybrid sealant for the plastic beckson ports up forward, also ordered new gaskets and screens for a reasonable price throught west marine. The windows I was tlaking about sealing are non-opening and the old gasket is unservicable. thanks for the suggestions.