How bad is this corrosion?

[AMG08]

Pulled the gas tank deck off the back of my boat because I noticed a little corrosion in the area and I wanted to take care of it. The picture shows what I found underneath.

Im not sure how far up it goes but I don't think its past the center console because there's a hole in the floor there for the baitwell and I don't see anything to this extent in there.

Im not sure why its so bad. Yeah boat gets used in saltwater, but every time it gets a thorough rinse inside and out, and I usually fill the bottom with water and let it all flush out the back. Do you think there's anything in there that is promoting the corrosion?

I planned to gut the boat out this winter to replace the floor so ill for sure find out how bad it is then. In the meantime im going to treat this area as best I can.

I plan to take a light wire wheel to the area and then some scotch brite. From there I will re-primer and paint. Anything I should b aware of doing this? Any better ideas. I hate to see my money just rotting away like this, especially when I think I've been pretty thorough in cleaning it. For what its worth the boat is 10 years old and I've had it for about a year. Before me it was occasionally used in saltwater but mostly fresh.

 

[T Man]

Doesn't look that bad from your pic. I think a wire wheel would take more metal than the corrosion. Go to Napa and buy a bottle or two of alumabrite to clean it. I'd be more worried about what the floor looks like under that foam

 

[PSG-1]

Use Ospho (phosphoric acid) to neutralize the corrosion, then rinse it off. Ospho is about the only thing that will dissolve the 'sugar' that forms on aluminum, without actually harming the aluminum itself, like many acids will do.

 

[AMG08]

Thanks for the advice. I took a bit of scotch brite to the area and most of the corrosion and paint comes off. I think im going to strip the whole area, apply a zinc chromate primer and paint. Any faults seen in that plan?

 

[PSG-1]

That's exactly right. Use the ZC primer before you paint, and you'll have no issues. Failure to use a self-etching primer on aluminum will ruin an otherwise nice paint job, as it will just flake off.

 

[AMG08]

So the story goes on with this boat. I noticed a corroded spot on the weld on the back left corner of the transom. I took it in and had a welder grind the corrosion off and re weld the spot. All was well for a couple trips then I noticed the spot was back. I opened the hole up a bit with a small flathead and cleaned it up after the picture was taken. Inside some white powder came out, along with a grey colored paste and some clear tacky liquid. I have to think it was because of the corrosion.

What would cause this spot to keep corroding? It is the exact same spot. I thought at first it was the dreaded G3 corrosion issue, and I haven't ruled that out yet, but this is the only spot doing it. The hole to the right also had a spot that was really soft and corroded so I ground it away and filled it in. Nowhere else on the transom is it doing this (yet) and the front deck is good with no issues.

 

[AMG08]

[attachment=-1]uploadfromtaptalk1400776830494.jpg[/attachment]

 

[PSG-1]

I have seen this condition occur when the wrong wire alloy is used, particularly in salt water.

It's important to make all welds on boats with 5000-series wire, such as ER5356, as it has corrosion resistance.

Do NOT use 4000-series aluminum, i.e. ER4043, as it is not rated for marine use, and it will quickly corrode, especially if it is used in or around water. I have seen spots on boats that were welded with 4043, literally fall out from corrosion. It turns to alka seltzer like substance real quick.

 

[AMG08]

That sounds like its it! Alka selzter. So if the guy that welded it used the wrong wire should I take it in and have it re welded?

 

[-coaltrain-]

Amg08.... depends on how long ago the welder made the repair.... being a welder myself, I dont think that would fall under the warranty work umbrella. Also it will be hard to prove what wire he welded with.

 

[AMG08]

-coaltrain- » 36 minutes ago[/url]"]Amg08.... depends on how long ago the welder made the repair.... being a welder myself, I dont think that would fall under the warranty work umbrella. Also it will be hard to prove what wire he welded with.

I would honestly probably take it somewhere else anyways. Wasnt a big fan of the place I went before. I think Ill put a few more trips on it and keep an eye out and see. Im REALLY hoping its something like this and not the G3 transom corrosion issue.

 

[Shoedawg]

I may have a little corrosion problem myself, near the stern and some spotted areas near the front and middle of my boat. I will look into the Ospho. Thanks for the tip.

Hope you can get that fixed AMG08.

 

[PSG-1]

AMG08 » 22 May 2014, 20:27[/url]"]That sounds like its it! Alka selzter. So if the guy that welded it used the wrong wire should I take it in and have it re welded?

Not by him....LOL Or, if you do have it welded by that welder again, you need to advise him of the ABYC and AWS standards for welding aluminum in marine environments, and which alloys are acceptable, which are not.

In any case, that bad spot will need to be drilled/ground out, then re-welded with the correct filler wire. That would be my assessment.

 

[PSG-1]

-coaltrain- » 22 May 2014, 20:32[/url]"]Amg08.... depends on how long ago the welder made the repair.... being a welder myself, I dont think that would fall under the warranty work umbrella. Also it will be hard to prove what wire he welded with.

Indeed. Without metallurgical testing, it would be very hard to determine exactly which alloy was used to make the repair.