Corrosion fix
- Thread starter QldGrady
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Hookup1
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Can't tell exactly where this is on the boat but it looks like a grab rail. You need to remove it and re-caulk with 3m 4000uv. Make sure you use 316 stainless bolts to put it back on. The rust stains can be removed with a spray rust remover but if you don't fix the problem they will come back.
hat is crevasse corrosion, caused by moisture seepage into the fittings. You can clean off the rust but it will come back. The only sure way to stop it is to remove the rail or handle, clean out the hole and the hardware, seal the hole if wet and rebed the rail.
If the item is the rail, it can be a pain and a big job to remove it. As long as you can get to the back to loosen the mounting hardware, you can try to lift it a half inch to get some access to the rust and clean it up. Then rebed as best you can and tighten down. Only tighten till you get squeeze out and then let it sit till the sealant sets up. Then retighten.
If the item is the rail, it can be a pain and a big job to remove it. As long as you can get to the back to loosen the mounting hardware, you can try to lift it a half inch to get some access to the rust and clean it up. Then rebed as best you can and tighten down. Only tighten till you get squeeze out and then let it sit till the sealant sets up. Then retighten.
What Seasick said. Crevice corrosion. Stainless works very well against corrosion/rusting unless it doesn't have adequate contact with oxygen. When water (stagnant at this point) stays in contact with the SS, this is what you get. Stainless = Stains Less 
This is a good application for butyl rubber tape, by the way.
This is a good application for butyl rubber tape, by the way.
Doc Stressor
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After cleaning and before re-bedding, you should re-passivate the stainless steel or the corrosion will come back. Commercial treatment uses nitric acid but that is pretty dangerous. I have had good luck with citric acid. Your best approach would be a commercial product that both removes the rust and re-passivates.
https://www.amazon.com/Citrisurf-Stainless-Steel-Cleaner-Removal/dp/B076CTWRVS
This stuff will remove the rust from the fiberglass as well if you keep it soaked using a rag and wait long enough.
I typically clean up the looser rust with Barkeeper's Friend before using a citric acid treatment.
https://www.amazon.com/Citrisurf-Stainless-Steel-Cleaner-Removal/dp/B076CTWRVS
This stuff will remove the rust from the fiberglass as well if you keep it soaked using a rag and wait long enough.
I typically clean up the looser rust with Barkeeper's Friend before using a citric acid treatment.
Another option for removal of the staining is something like Rust Out or Iron Out. These are both readily available at Home Depot and are specifically designed to remove rust staining. They work very well for this - mist it on and let them do their magic.