Removing Bottom paint from Aluminum?

freeisforme

Petty Officer 2nd Class
Joined
Mar 23, 2009
Messages
184
I looked at an aluminum boat last week which was in a local free paper for sale. When I went to see it the owner was in the process of swapping over his motor and seats to a larger hull. We agreed on a price, but the seller told me he wanted to get the other boat going before he sold the old one. The boat was in nice shape, all original, but needed some cleaning up and some new wood in the transom.
I went back to get the boat last night and found that the owner decided to do me the favor of painting it. He rolled the top side with enamel, which looks OK, he painted the rotted transom wood, no big deal, but he coated the bottom real heavy with copper based bottom paint, that old green stuff they used to use on wood boats.
I know it can't stay, copper + paint + aluminum + saltwater = Battery effect.
I got the boat super cheap, almost free, so I can't complain, I just loaded it up and left. The boat originally had a polished aluminum underside and it don't appear he sanded it or anything before painting. But it's on there thick.
I tried paint stripper but no go, it don't touch the stuff, its like a dry chalky coating that rubs off when you touch it. I got a good bit off with a scrub brush and dish detergent, but that will take a month. I did some with a pressure washer but that didn't work as well as the brush did.

Any ideas? It's a 16' boat and more than half the outer hull is coated. I suppose he put at least a gallon of the stuff on there. The hard part will be getting it off around the rivets and keel strip. It's also got 4 riveted on strakes that area also bleeding green paint. The stuff is dry, even where he dumped it on heavy but doesn't chip off. I made the best progress so far with hot water and a block of wood wrapped with some old wool carpet I found in the attic. My plan is to get this stuff off and give the thing a good coat of epoxy paint or maybe even polish it back to the way it was new.

If he hadn't painted it, I probably would have just hung a motor and gone fishing, it didn't look that bad in the first place but the fact that this is copper based paint, makes it a priority to get off there.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,099
Re: Removing Bottom paint from Aluminum?

Ayuh,... A 4" grinder,+ a SSteel cupbrush come to mind,...
'course,... So does just Scrappin' it...
 

freeisforme

Petty Officer 2nd Class
Joined
Mar 23, 2009
Messages
184
Re: Removing Bottom paint from Aluminum?

I'm afraid a cup brush would leave me with some rough looking aluminum afterward? I've gotten about half of it off with the 2x4 block with carpet attached and some hot water and Dawn dish soap. It's the areas around the rivets that'll be the problem since every rivet is sort of recessed into the aluminum making them flush to the touch. I'm thinking maybe going and getting one of those cheap Soda Blasters at Harbor Freight?
 

freeisforme

Petty Officer 2nd Class
Joined
Mar 23, 2009
Messages
184
Re: Removing Bottom paint from Aluminum?

I figured I'd update on what worked best here, I first hit the whole thing with a hot pressure washer, then scrubbed it with kitchen cleanser and a carpet covered piece of 2x4, then I followed up with a foam pad on a 7" buffer with some polishing compound and it got all but a few thick spots here and there that the buffer couldn't reach, so I got those with a razor blade and polished up those areas. I could go further but I'm happy with just a clean look.
The foam pad got in around the rivets, at some expense to the pad but they're cheap and I gladly wasted three foam pads to save a few days work otherwise.
80% of the stuff rubbed right off with just the cleanser, the rest spun away with the buffer.
 

arcadiainc

Seaman Apprentice
Joined
Jun 26, 2002
Messages
33
Re: Removing Bottom paint from Aluminum?

Go to Harbor Freight and purchase a soda blaster and 50 pounds of blasting soda. You will need an air compressor. Will run you less than $200.00. Great item and quality built. I purchased one for paint removal on antique outboard motors. To date I have cleaned two motors. The last a 1966 Johnson 20 HP that had been poorly and heavily camoed. The blaster worked great taking the surface down to bare aluminum with no damage or pitting. I walked into a Harbor Freight to have a look and saw the blaster signed $79.95. Bought it and fifty pounds of blasting soda for less than $130.00. Best money I have spent on shop tools in a while. Oh! my compressor is an old one HP model setting on a sixty gallon tank. Works well.
 
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