Filling in pitting before priming and painting

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Douglasdzaster

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Hello everyone, this is about my third thread since all this started. I found a Jon boat a while back to fix up and go fishing. I did the motor work first instead of checking other things like I should have being my first aluminum boat. I got it going and had been using it a lot.
The more I learned about aluminum I decided to pull the floor and clean under it. Looks like it was coated with either roofing material or bed liner I could be wrong. I noticed pitting in the cross members and decided to just redo the bottom if not paint the whole boat. The boat never leaked but I have found several patches and bumps it must have received on the near by river. Anyway water was staying under the floor after it got wet and was moist when I removed it so I think that’s the source of the corrosion. Unless the po used it in saltwater.
The more coating I removed the more I found. Some spots even looked like rust but aluminum doesn’t rust I’m told. So I kept on going taking it to bare aluminum. My questions now are what should I fill in the pitting and old screw holes with all corrosion is removed? I’d like to use something that will help the cross members stay strong if possible. Pitting on the actual floor is shallow thank goodness. And as I get to the bilge area there are places I can’t get to. What do I do there? It’s taking me over a month due to having to work outside with the weather here in Texas. I now have a cover that I use when not working on it and for when I’m finished. I pal on putting a floor back in that’s easy to remove and keep the bottom clean and dry. When I started this I was advised to leave it alone since I stay in freshwater but other things I found and had to redo that the po had done made me worry about the corrosion continuing to eat it like a cancer.B313209D-E986-441D-9A74-848DFEB5C6DC.jpeg D2AA74F6-AEA8-4383-A5D0-F3A4A374E2D0.jpeg 68A4EB3A-EBBC-4412-AE2D-2C50CA65E88B.jpeg . Thanks for any advice or opinions. Oh the actual holes in the cross members are from rusted broken screws that attached the floor which were rusted and I removed what was left of them with a Dremel tool.
 

DaleH

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Concern - At just test a few spots, poke with ice pick, awl or drill tiny hole in any pit. Do you see any evidence of WHITE corrosion? Aluminum can develop a self-perpetuating corrosion phenomena called "preciptate chloride corrosion" ... usually on boats in saltwater use. On a SW boat I had, the total refurb of new transom skins in my signature, as the test hold got bigger and bigger, I was still seeing a white layer inside the tin. You might need good light and a magnifying glass.

If 'no' to the above, and whereas freshwater use only, my best advice would be to keep her clean and dry, as water or moisture helps cause where tin can corrode. You might want to scrub all areas with white vinegar on a copper scrubbie, then rinse, as the etches the tin back to a self-protecting oxidized layer.

If pits OK, I think 'clean & dry with fresh air' (make sure cover has ways to vent or air out, etc., is your best option! You could fill the pits with a good epoxy, but then the area would need to be primed beforehand and painted over afterwards (epoxy can't survive sun exposure ... ) and it really wouldn't add any strength anyway IMHO, so I'd likely not even bother.
 

Douglasdzaster

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DaleH said:
Concern - At just test a few spots, poke with ice pick, awl or drill tiny hole in any pit. Do you see any evidence of WHITE corrosion? Aluminum can develop a self-perpetuating corrosion phenomena called "preciptate chloride corrosion" ... usually on boats in saltwater use. On a SW boat I had, the total refurb of new transom skins in my signature, as the test hold got bigger and bigger, I was still seeing a white layer inside the tin. You might need good light and a magnifying glass.

If 'no' to the above, and whereas freshwater use only, my best advice would be to keep her clean and dry, as water or moisture helps cause where tin can corrode. You might want to scrub all areas with white vinegar on a copper scrubbie, then rinse, as the etches the tin back to a self-protecting oxidized layer.

If pits OK, I think 'clean & dry with fresh air' (make sure cover has ways to vent or air out, etc., is your best option! You could fill the pits with a good epoxy, but then the area would need to be primed beforehand and painted over afterwards (epoxy can't survive sun exposure ... ) and it really wouldn't add any strength anyway IMHO, so I'd likely not even bother.
I could see white corrosion in the pits and a Nyalox brush on a drill cleaned it out to the metal. At least as far as I could see. I’ll test several areas and use a magnifying glass. While removing the coating there where spots that had moisture under the coating. Several of the channels where clogged with all kinds of things. I also ran a flexible magnet in each cross member and found screws,nuts,hooks, and something’s so rusted they where unidentifiable. I have some Krudd
Kutter metal clean and etch I was going to use. It’s supposed to remove any oil etc. and etch at the same time. I’ll go with vinegar if that’s better.
I was also going to prime and paint for protection. Do you think the oxidized layer is just as good? (That would make things a lot easier and affordable.)Lol If it makes a difference I’m putting a floor back in over it.It will be easy to remove whenever the inside does get wet and to clean.
The main reason for the floor is , the boat is a 1983 Monark and the floor will help keep pressure off of the old rivets. Like I said it hasn’t leaked but I did find a few patched spots and the boat has a thick coat of what I think is black epoxy underneath.
Thanks for replying. I appreciate any wisdom shared. I’ll report back about the test spots. It may be a day or two looking at the forecast.
 

Douglasdzaster

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DaleH said:
Concern - At just test a few spots, poke with ice pick, awl or drill tiny hole in any pit. Do you see any evidence of WHITE corrosion? Aluminum can develop a self-perpetuating corrosion phenomena called "preciptate chloride corrosion" ... usually on boats in saltwater use. On a SW boat I had, the total refurb of new transom skins in my signature, as the test hold got bigger and bigger, I was still seeing a white layer inside the tin. You might need good light and a magnifying glass.

If 'no' to the above, and whereas freshwater use only, my best advice would be to keep her clean and dry, as water or moisture helps cause where tin can corrode. You might want to scrub all areas with white vinegar on a copper scrubbie, then rinse, as the etches the tin back to a self-protecting oxidized layer.

If pits OK, I think 'clean & dry with fresh air' (make sure cover has ways to vent or air out, etc., is your best option! You could fill the pits with a good epoxy, but then the area would need to be primed beforehand and painted over afterwards (epoxy can't survive sun exposure ... ) and it really wouldn't add any strength anyway IMHO, so I'd likely not even bother.
Thank you Dale. I wanted to let you know I appreciate your advice. I put a tiny engraving bit for soft metal on my Dremel and strarted checked pits. I just thought I had all the corrosion out! It’s been tedious but with a magnifying glass I’ve been chasing the corrosion until I hit good metal. It’s made some of the pits a little bigger but not any worse than the rest. I’m crossing my fingers I don’t find one that there’s no end to or goes through the bottom.
If I make it ok. Im going to use a degreaser cleaner I found then give it an acetone wipe down (probably going overboard) Then I’m thinking of going ahead and putting a coat of polish and then some Star Brite protectant. No epoxy. I’ll keep it clean and dry and every so often give it a deep clean and reapply polish and protectant. I’ll have a floor over it that will be easy to remove often so no moisture or grime gets started.
 

DaleH

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Douglasdzaster said:
... If I make it ok. Im going to use a degreaser cleaner I found then give it an acetone wipe down (probably going overboard) ...
I'd just use cheap white vinegar and a copper scrubbie brush/pad. Rinse well. The vinegar will 'etch' the tin. Clean and dry will go a looooong way to keep her ship-shape for you!

Good luck! You owe us pictures when done :D ...
 

Douglasdzaster

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Dale, do I keep cleaning the pits as I’ve been doing or use the vinegar and copper scrub now? I’ve tried vinegar to remove the white corrosion from in the pits and it didn’t. Does vinegar neutralize it though? I’ve also tried baking soda with and without vinegar.
Heading out now to apply more vinegar and scrub with the copper and check that out.
I have some Krudd Kutter metal clean and etch that says it’s safe for aluminum but haven’t got desperate enough to try it. Don’t know if I should trust it. Lol
I don’t know if you want pictures. Lol It’s going to be scratchy because I had to get aggressive removing the coating and I’m just doing it to fix the corrosion not going to 500 grit wet sand , lol. I’m ready to get back on the water. Besides the old boat could use a complete make over but that’s coming later down the road.60E8088F-01C7-4020-B29B-6011C244D897.jpeg
 

Douglasdzaster

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Well I ended up polishing the inside of the boat so I could keep an eye out for corrosion. It’s been 7 months and It’s in good shape.
I just posted a new post with a question about the way I’m thinking of re coating it. So look for my question about painting post.
Thanks
 

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