Hull corrosion in bilge area

General boating discussion
PNW Workboat
Posts: 2
Joined: Sat Jan 04, 2020 10:46 pm

Hull corrosion in bilge area

#1

Post by PNW Workboat »

Hello all and thanks for having such a great online forum about aluminum boats.

I am currently in the process of improving a 1982 30’ aluminum workboat and noticed some strange looking corrosion in the bilge area. It appears to actually be actively “fizzing” and creating little raised white clouds of corrosion?
This occurs in the hull area where 2 8d batteries where formerly located. The hull is 1/4 aluminum FYI.

I have searched the forum, but have been unable to find an answer to this weird looking corrosion.
Can I neutralize this somehow?

Thank you in advance!
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kmorin
Donator 08, 09, 10, 11, 12, 13, 14 15, 16 17, 18, 19, 20
Posts: 1530
Joined: Mon Aug 18, 2008 1:37 am
Location: Kenai, Alaska

Re: Hull corrosion in bilge area

#2

Post by kmorin »

PNW,
I don't believe I've seen that particular corrosion 'growth' or type before- so all I can do is speculate!

First, if this is in the battery compartment, perhaps the acid/water/mixture isn't correct and you've been evaporating some higher acid content vapor? (Speculation only) If you're charging or overcharging due to age of the cells, or mixture in the cells, and that has resulted in an acid vapor discharge?? perhaps this forms as a result?

Any acid based corrosion can be neutralized by spraying with a sufficiently base water solution. So if you mix a few gallons of warm (or hot) tap water and add a couple tablespoons of house hold ammonia- then spray that compartment?- well that will stop any acid caused corrsion?

First, for informational purposes- I'd want to sand/buff/wire brush a few of these areas to see if there is any surface pitting/corrosion ? under the 'flowers'?? The reason is infer if the sites we see are a result of the surface coating of unknown origin? OR if these sites are a later event caused by some source we/you/the Forum hasn't determined?

I'd want to pressure wash the entire inside of this compartment- not just for the white flowers but for the incredibly thick surface contaminant film -sort of greenish gray layer of 'something' coating the compartment in the photos.

Not sure if I'm helping, but then I've never seen a compartment so coated with ANYTHING before!!

cheers,
Kevin Morin
Kenai, AK
kmorin

PNW Workboat
Posts: 2
Joined: Sat Jan 04, 2020 10:46 pm

Re: Hull corrosion in bilge area

#3

Post by PNW Workboat »

Thank you Kmorin,
That is good to know this is not normal and I that I am dealing with something out of the ordinary. I looked all over for more info on this and came across something called poultice corrosion and I was not sure this was the same thing.
In your experience, would baking soda work as well as ammonia? I worry about the vapors in a confined space but want to use whatever works best.
Not sure if this is worth mentioning, but the bilge had old kitty litter and general debris so I vacuumed and pressure washed it out. During the pressure washing, I wonder if I spread the acid out during the washing process and now need to neutralize it?

Thanks again for the info and help, I’ll get out there and report back after I clean it up more.

kmorin
Donator 08, 09, 10, 11, 12, 13, 14 15, 16 17, 18, 19, 20
Posts: 1530
Joined: Mon Aug 18, 2008 1:37 am
Location: Kenai, Alaska

Re: Hull corrosion in bilge area

#4

Post by kmorin »

PNW Workboat wrote:
Sun Jan 05, 2020 9:32 pm
That is good to know this is not normal and I that I am dealing with something out of the ordinary. I looked all over for more info on this and came across something called poultice corrosion and I was not sure this was the same thing
poultice corrosion is usually a form of crevice corrosion where an absorbent is allowed continued wet contact with the alum. So open walls like this is not poultice corrosion in the most common sense.
PNW Workboat wrote:
Sun Jan 05, 2020 9:32 pm
In your experience, would baking soda work as well as ammonia? I worry about the vapors in a confined space but want to use whatever works best.
dilute vapors of ammonia aren't going to cause damage but baking soda solution will work- just a bit more powder in water to get similar pH.
PNW Workboat wrote:
Sun Jan 05, 2020 9:32 pm
Not sure if this is worth mentioning, but the bilge had old kitty litter and general debris so I vacuumed and pressure washed it out. During the pressure washing, I wonder if I spread the acid out during the washing process and now need to neutralize it?
having no idea the chemical make up of kitty-litter- using it as an absorbent or to help clean the bilge is outside my experience- but there could a real contribution to the corrosion shown by some unknown chemicals in the kitty litter?

Washing will move the acid around, but the dilution factor should be many times higher than floating the acid to new locations. So just running garden hose will dilute acid bilges hundreds of times- shifting pH to a safer range just by dilution.

Cheers,
Kevin Morin
Kenai, AK
kmorin

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