Quote:
Originally Posted by Kern O
I am making rapid progress on setting up the new to me Venture 34. It is currently in Los Angeles where I am adding dive ladders, windlass, new electronics and on and on and on.
Right now, all the aluminum is anodized. I can have it all powdercoated without a problem BUT I have to do it here and once it gets to Maui, it cannot be re-done. On the SeaHunter 29 thread, John (Darbikrash) has voiced his frustration with trying to keep anodize looking decent. My Stamas was all anodized and held up pretty well, but was beginning to pit after a few years. The Jupiter was all powdercoated, but I never got a chance to find out how it worked before the boat was destroyed.
If I had access to powdercoating, I'd leave it anodized and then powdercoat it when it got too pitted. I know that a lot of people hate powdercoat becasue they've had problems with it blistering, usually where a stainless screw sets up a glavanic field and causes the powdercoat to lift. Once the corrosion starts, it spreads and there is nothing you can do.
Before they powdercoat, they sandblast the aluminum, so it does not matter if it was anodized or not once it gets to the powdercoater. I'd love to put powdercoat right over hard anodize, but I'm told it won't bond well enough.
Opinions?
John: Can they mask powdercoat so the top is coated but the weld on rod holders are not?
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Yes, they can mask off the powdercoat. In my case, the weld for the gusset to the pipework must be made “in the field” and the weld from the gusset to the tulip rod holder is made by Birdsall, and this weld is anodized. I don’t like welds that are not anodized or in some way treated, so I’m going to powdercoat over the field weld and mask just forward of the weld line, so as preserve the gusset/rod holder anodize and yet still give a place for the powdercoat to “bite” on the field weld.
A few words about anodize. “Hard” anodize or Type 3 class III, has a pretty deep surface penetration, usually .001-.003/inch, although it can be deeper, with a buildup of a similar thickness. A common callout is .001 penetration/.001 buildup. Sandblasting may not entirely remove the surface penetration for a Type 3 Hard Anodize. The more common Type 2 class II, or surface anodize, is a cosmetic surface treatment that should come off pretty well with sandblasting. Areas not entirely cleared may not hold powdercoat properly, and these would be areas of risk for peeling.
The secret to good adherence of powdercoat is threefold, surface prep, no galvanic fields, and protection against fastener head chipping.
For surface prep, sandblasting is a good start, but it must be followed by a good quality primer. For the best success stories relative to paint adherence to aluminum, look at the aircraft guys. Not many airplanes have paint coming off aluminum skins even at 600 mph. They use Alodine primer, ( I believe it’s electrolytically applied) by far the best aluminum primer. This is that flat green stuff you see on Mil Spec aluminum parts (and unassembled aircraft). I know Jupiter had many warranty issues with their trademark powdercoated pipework, until they switched to a powdercoater that figured this out. Now, no warranty issues. Other primers may work as well, but why argue with the aircraft people?
For galvanic corrosion, I would think some of the galvanic compound paste applied to CRES fastener threads would make this go away relatively easily.
And the last issue, and perhaps the hardest to deal with is the use of fastener heads screwed down tight on powdercoated surfaces. These high point loads almost always fail the coating before the boat is even splashed, and propagate into ugly sections of chipped paint. If you look closely at the way Everglades puts together their pipework, you will see that in every case they use a very hard plastic washer under the fastener heads to prevent the bolt from digging into the coating. I don’t think you can buy an anodized aluminum structure from Everglades, it’s 100% powdercoat or nothing.
All this stuff is nitpicky and difficult to do properly. If one if these steps is not done just so, the powdercoat will fail. For some, it may just be easier to forego the powdercoat and deal with the maintenance.
Not me though.
Powder coat? Yes or no?
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