Is this corrosion?

The problem with styrofoam is that if it gets any gas on it, it just disappears, and dissolves away, there are better alternatives out there today. (styrene foam, Styrofoam is actually a trade name I believe)

surfman said:

The problem with styrofoam is that if it gets any gas on it, it just disappears, and dissolves away, there are better alternatives out there today. (styrene foam, Styrofoam is actually a trade name I believe)

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the XPS boards (blue, pink, or green insulation boards) that most people on here are using today are the same material as styrofoam (they are both polystyrene); it's just a different manufacturing method (extrusion) which results in a solid piece rather than the little foam beads. either can dissolve if exposed to gasoline, so just try to avoid pouring gasoline down in the bilge.

the more expensive two part polyurethane foams that you pour in place are gasoline resistant, but you hardly ever see folks here using that

After doing some more reading on mill scale I'm thinking I may have a project for this winter. Appreciate if you'd keep us up to date on your progress.

minuteman62-64 said:

After doing some more reading on mill scale I'm thinking I may have a project for this winter. Appreciate if you'd keep us up to date on your progress.

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Will do!

Got some phosphoric acid etch and supplies at the Home Creapo today ... going to have a hand at removing the milscale tomorrow...

BTW, galvanic corrosion can occur whenever there is a potential (voltage) difference between the hull and ground, and there is an electrolyte (conductor) between the hull and ground. Thus - if you have a battery connected to the hull (electric start Mercury motor), and an electrolyte to ground (wet, salt-soaked bunks), galvanic corrosion can occur.

Different metals against each other (like aluminum and copper) actually create a potential difference in the presence of an electrolyte. The junction is a battery, and like any other battery, the less noble element corrodes as it produces power. It seems that's what everyone usually thinks of when they talk of aluminum corrosion.

I don't know squat about aluminum boats, but my undergraduate degree was in Materials Science. It's not made me much money, but the upside is I'm now super paranoid about my boat! #-o

sonicwonder2000 said:

Got some phosphoric acid etch and supplies at the Home Creapo today ... going to have a hand at removing the milscale tomorrow...

BTW, galvanic corrosion can occur whenever there is a potential (voltage) difference between the hull and ground, and there is an electrolyte (conductor) between the hull and ground. Thus - if you have a battery connected to the hull (electric start Mercury motor), and an electrolyte to ground (wet, salt-soaked bunks), galvanic corrosion can occur. #-o

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What was the name of the stuff you got at Home Depot? In paint dept.?

Still wrestling with the corrosion issue w/batter hooked up in boat (actually, I'm lazy and looking for a rationale to not un-hook the battery every time I put the boat back on the trailer ). The (limited as it may be) reading I've done on galvanic corrosion indicates that, like electrolysis, two different metals in solution are operative. Also, appears in the situation you describe, there'd be a current flow between the hull (at the -12V potential) through the carpet and the wood bunks to the metal of the trailer and to the ground. Isn't a return current flow to the battery necessary to have this occur? Otherwise, seems like I could discharge my battery by hooking up the "-" terminal to a rod driven into the ground.

On a related note, visited the Shelter Island launch ramp yesterday p.m. and talked to owners of 2 mid-19990's Bayrunners and one early 1980's Gregor. Asked them if they'd done anything about mill scale like etching/buffing/etc. Got blank stares in response. One guy stated that he'd bought his Bayrunner so he ".... wouldn't have to worry about that s**t."

None of the boats had the "flowering" quite to the extent that mine does. After a lot of reading on "the other site" I've concluded that, regardless of cause, it is not good to leave this "flowering" since it will hold water/salt and cause continued problems (buffing a small area I did notice slight pitting under the areas where the "flowers" were located). So, I'm planning on removing it. But, I'm wondering if maybe the Gregor and Bayrunner folks might actually have removed mill scale after all and the "flowering" on mine is a result of something going on during the almost 20 years it sat dormant on rotting, saturated bunks.

minuteman62-64 said:

What was the name of the stuff you got at Home Depot? In paint dept.?

Still wrestling with the corrosion issue w/batter hooked up in boat (actually, I'm lazy and looking for a rationale to not un-hook the battery every time I put the boat back on the trailer ). The (limited as it may be) reading I've done on galvanic corrosion indicates that, like electrolysis, two different metals in solution are operative. Also, appears in the situation you describe, there'd be a current flow between the hull (at the -12V potential) through the carpet and the wood bunks to the metal of the trailer and to the ground. Isn't a return current flow to the battery necessary to have this occur? Otherwise, seems like I could discharge my battery by hooking up the "-" terminal to a rod driven into the ground.

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The stuff at Home Depot is sold under the "Klean-Strip" name, it's called "Phosphoric Etch and Prep" and it's a green liquid, in a 1 gallon jug with a yellow label. It's in the paint dept. with all the paint strippers.

As for eliminating the current while the boat is trailered, use a battery disconnect switch. That will also eliminate any battery drain caused by any devices in your boat that may pull small amounts of current.

PSG-1 said:

As for eliminating the current while the boat is trailered, use a battery disconnect switch. That will also eliminate any battery drain caused by any devices in your boat that may pull small amounts of current.

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Protocol for disconnect switch seems to be to switch the "+" terminal. That would take care of any current leakage causing battery drawdown, but, since ground would still be connected to hull, the question of corrosion caused by contact between the grounded hull and wet bunks would remain (I think).

If the live terminal is disconnected, there will be no current flow and hence no electrolytic corrosion.

Sorry for the late response, work has had me more than a little busy :/

I finally finished 1/2 the boat etch this weekend - that acid etch is nasty stuff. My boat sides are pretty much white now - but the "complexion" is quite streaky. I'm not too concerned about it because this is mostly going to be a workboat.

The hard part of this process was that the acid does not stay put on the vertical surfaces of the boat; it runs down and collects on the chine(s); the bottom ends up with a more thorough etch than the top. As a result, I had to repeat the process three times on each 2' stretch of the boat. In an attempt to get a little more "action" from the acid, I applied it, and then scoured with a green scotch pad; that helped a little, but caused more streaking where the acid was worked in. I also tried heating the solution in the microwave prior to application and that was a BAD idea ... the thin layer of acid clinging to the container sides heats up much faster than the bulk of the container, and causes the acid to start attacking the container!

I've yet to do the bottom of the boat. So far, I've used a gallon and a half on my 19' boat ... I'm tempted to grab another gallon and have a go at the sides again, if for no other reason, to take care of some of the "streakyness". There are still areas of "flowering", they look almost like waterspots. I'm not sure if I should be attempting to remove these with abrasion ...

Time only will tell if this process helps.

Did you use the Klean Strip phosphoric etch and prep that I see in HD?

Did it remove the little blisters (maybe that's what you refer to as "flowering")?

Is your boat on a trailer? If so, any effect of the etch solution on it?

Sorry for all the questions, but, inquiring minds (that might be doing the same thing) want to know

The "sugar" or "flowering" may take several applications of the acid to get in there and work its way through that corrosion. You can speed up the process by using a stainless wire brush on the worst areas.

@Minuteman:
-The stuff I'm using is the Klean-Strip phosphoric etch an prep
-My trailer is galvanized and it foamed WAY up when the acid touched it. Now I have a REALLY clean trailer ;-)
-My carpeted bunks have been covered with a pvc glide strip, so there should not be direct acid contact between the null and the carpeted bunks.

Here are some pics of the half completed effort. Although the "flowering" has gotten better, it hasn't completely gone ...

Questions:

1) I'm wondering if I need to apply more elbow grease? I'm using the Klean Strip Phosphoric acid wash undiluted, so other than trying another more concentrated brand, I can't do anything there. Also, I cannot leave it on for more than a few minutes because it tends to dry before it starts to "foam". The results you see are after three applications of the acid wash - but the second and third applications were on a wet hull, and this might have diluted the effectiveness somewhat.

2) Being the first time I've done this process, I'm not quite sure how to proceed. In some ways, the hull looks worse than it did before because of the streakyness, but I'm doing this for corrosion prevention, not looks. Do I need to remove all trace of these waterspot like areas of corrosion? The acid etch seems to have almost hilighted those areas because they are even whiter than the surrounding area. However, the aluminum is very smooth to the touch ...

If you've done 2 or 3 applications of the phosphoric acid, at this point, you've pretty much taken care of the corrosion. Best course of action now is to apply a coat of underwater primer suitable for metals, i.e. interlux inter protect primer. Then a coat of bottom paint, or at least some type of durable epoxy paint.