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post #1 of 2 Old 07-10-2019 Thread Starter
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Bronze matching necessary?

I have replaced a 1.5 inch valve and thru hull, after only a few months in brackish (upstream Chesapeake) water there's green verdigris on both near connection. Hard to believe its leakage, was very careful with thruhull installation and used Sikaflex 291 long setting, but I am fairly new to the procedure - have done half a dozen and there's no evidence of leakage on any of them. I did connect a bonding wire to the valve, have not yet installed a galvanic isolator. She was in the water when it froze over, but bubbler/circulator kept most ice away from the hull. Also note that the valve has never been connected to any plumbing at all.

Two questions - could this be galvanic corrosion due to metal mismatching? Valve is Groco IBV 1500, 400 WOG, don't know what the thruhull is. If it is, how does one go about matching metals on thru-hull and valve? What else am I missing?

Second, if its leakage, should I also be worried about osmotic action in the hull itself? I cleaned and scraped the hole but didn't prep it with anything - should I paint the hole with epoxy or something before installing the thru-hull?
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post #2 of 2 Old 07-11-2019
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Re: Bronze matching necessary?

Green verdigris is usually not a sign of anything other than some salt water contact. It's a protective oxidation that actually protects the metal. If you see pinkish color you need to be concerned because that's electrolysis and can do serious damage in a short period. Might check carefully to see if there is any water weeping through the threads or valve. Did you use pipe dope on the threads of the through hull, valve, and hose fitting?? The paint on stuff, which I believe is teflon based, goes a long way to protecting the threads from corrosion and sealing up minute imperfections in the threads that can weep water.
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