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Corrosion under hull paint
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scubaJ
#1 Posted : Tuesday, June 14, 2011 9:53:03 PM(UTC)
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I have a 37' sedan bridge [1978]that is showing what looks like "pimples" under the hull paint. The paint is tight and has no visible cracks, but for each of the last few years, when i wax the hull [boat is hauled and stored in a building all winter] there seems to be more and more areas showing the little bulges. The owner of the storage/repair facility has ythe opinion that it is corrosion. I have owned the boat for about 7 years. He thinks that on a previous repaint, that the painter did not get corrosion cleaned up before painting, and it's now showing itself. Any thoughts or advice. Think I should start thru the drill for sources of electrolysis? Near as I can determine hull was painted about 15 years ago. Boat in Ohio River, so it's fresh water and berthed in a marina for season. Capac reads under 7 most of the time [when I think to check]. Paint is ostensibly imron, but it shows some sign of wear in locations where previous owner had fenders rubbing. Magnesium at keel, on rudders, on trim tabs and on shafts
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GB49
#2 Posted : Wednesday, June 15, 2011 1:56:40 AM(UTC)
GB49

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The Imron is bubbling, not the anti-fouling paint, correct?

Imron will bubble if it cant breath, especially if the boat is stored with a plastic/shrink wrap cover. The bubbles usually go away once the paint is exposed to the air.

I have also seen Imron bubble in areas where the bondo (lots of bondo on these boats) reacts to the paint. This usually occurs in corners where lots of filler is used.

Can you try using a pin to pop one of the bubbles. See if they are full of air or water or crusty corrosion?

Perhaps part of the hull was damaged in the past and fairing compound was used across the hull before repaint? I guess that depends on how clustered the bubbles are.

Make sure no 12V equipment is grounded to the hull.
Shore cord is healthy (blackened ends etc) and not leaking voltage to the hull.
Neighbors shore cords are healthy and not leaking voltage.
Marina bulkhead, if present, is not leaking voltage into water....Check for stray voltage between neutral and ground. Bulkhead should be connected to ground.

-Karl
1986, 32' Sedan, twin 360ci, 275hp Chrysler's w/ K&N flame arrestors
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1 user thanked GB49 for this useful post.
Bill on 6/16/2011(UTC)
Barkleydave
#3 Posted : Friday, June 17, 2011 7:27:26 AM(UTC)
Barkleydave

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Paint bubbles when there is a loss of adhesion. (Thats Obvious)

#1 Cause: Surface contamination.

Imron paints are excellent coatings however surface prep. is VERY CRITICAL. Any spots missed or barrier coat get moisture the coating will lift.

Do not confuse coating failure blisters with fiberglass osmosis blistering.



dave
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scubaJ
#4 Posted : Wednesday, June 22, 2011 8:05:38 PM(UTC)
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Boat stored on the hard in a barn all winter-no shrink wrap-yes it's the hull paint above waterline and above anti fouling. I will try the pin pop. Also will try to track down any 12v grounding to hull. The paint is pretty old [15-20 years, maybe. Some of the former owner's records indicate that the white [hull] paint was Awlgrip if that makes any difference. I am hardly an electrical troubleshooter, so I will dig in the forum for some helpful suggestions
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