Aluminum Bottom Inflatable-Powder Coating Flaking off

[CruisersCaptain]

I have a Zodiac RIB with an aluminum bottom and the powder coating is flaking off at the bottom of the transom. I had this happen on the first inflatable I purchased and Zodiac replaced it under warranty. It is happening on the replacement as well. The only thing I had done to both is to use Alumi-Koat water based bottom paint. The dinghy stays in the water most of the time. I doubt Zodiac will replace the inflatable again. Any ideas on a possible cause and if I have to repair the bottom myself, what to use? Thanks.

[a64pilot]

In my opinion, any powder coating on any aluminum surface will eventually fail. It’s not the fault of the powder coating, it’s because the aluminum will eventually corrode and the coating will flake off, so the aluminum, not the coating fails.

Having said that last boat I made the radar mount from aluminum and welded it together, I was going to have it powder coated by the business that powder coated all the aircraft fuselages we built. He told me I need to anodize it instead, but where it was welded would turn black. So he anodized it, then powder coated it. The coating lasted because the anodized aluminum didn’t corrode.

But I don’t think any dinghy manufacturer anodizes before powder coating.
If highfield would have sold a bare dinghy I would have bought one, but they won’t. So I bought an AB, because I feel powdercoat will eventually fail. No matter how well done it is.

It is much better looking than bare aluminum though, until it starts coming off.

Repair wise, just paint it, but your fighting a losing battle, in my opinion.

[CruisersCaptain]

Thanks. Defender said they sold hundreds of these inflatables and I'm the only one who has had an issue. I find that hard to believe. Any suggestion on what I use to paint and seal it?

[Shrew]

Originally Posted by CruisersCaptain

Thanks. Defender said they sold hundreds of these inflatables and I'm the only one who has had an issue. I find that hard to believe. Any suggestion on what I use to paint and seal it?

Ah yes, the old "Blame the owner for the shortcoming of the product" ploy.

Defender has sold hundreds and yet to have anyone report the issue.

Defender has sold hundreds and that particular employee hasn't personally processed any complaints.

Poor customer service to shame the customer for a product defeciency.

powder coating on aluminum will fail eventually. The aluminum oxidizes under the paint layer and lifts the paint layer. It is what it is.

[Jim Cate]

Contrary experience:

We have a Gemini alloy RIB, whose hull was made by Swift here in Oz. It is now about 16 years of age, near constant use. When it was quite new it was stolen, the outboard removed and petrol poured into the hull and lit afire. We got back some charred rubber and a scorched hull. The rubber nonskid in the hull was melted. Ugh...

I cleaned it up and had new tubes installed. Wore them out in about 6-7 years and had yet another set of tubes glued on. After all this time and abuse, the powder coating has not failed. It has been scraped and gouged off the bottom in places (we don't baby it!), but it has not lifted anywhere.

The folks at Swift made big claims about how much prep they put into the powder coating on their hulls. I dismissed it as vendor BS, but in fact it seems that it was indeed very effective. I don't know what their product is like now, but if one wants an alloy hull boat with powder coating, they'd be worth a call.

Jim

[ttex]

Did a Mexican cartel steal your dinghy, Jim? Holy moly!

[CruisersCaptain]

Can anyone recommend a primer, paint or sealant to apply to prevent further flaking?

[s/v Jedi]

Originally Posted by CruisersCaptain

Can anyone recommend a primer, paint or sealant to apply to prevent further flaking?

So you leave it in the water which means you need a below the waterline paint system. Google for it and I think you’ll need Alodine conversion followed by (example) Awlgrip 545 epoxy primer. Maybe you can use Interprotect 2000?

[mikedefieslife]

You would need to sand until shiny metal then prime within 30 mins or less better. Alexseal Cor Spec will do the business. You can then paint over that. Best within 3 hours, otherwise you have to sand again.

I would just leave it bare aluminium though and let it enjoy its natural protection from the elements.

[a64pilot]

Alodine as Jedi suggest is a chromate conversion process that’s used in aviation to protect aluminum on some aircraft, it’s not easy or cheap for a manufacturer to so it’s not always done.
Aircraft I built, every aluminum part was alodined, we had large alodine tanks that we ran all parts through prior to painting.
It helps, isn’t perfect but helps.
It’s not particularly friendly to the environment as it’s chrome, so don’t just throw it away.
https://www.aircraftspruce.com/search/search.php

I also instituted having the 4130 steel tube fuselages Powdercoated after seeing Maule fuselages on seaplanes in the Bahamas didn’t show any rust when being fabric recovered.

I don’t have a clue what was done to Jim’s dinghy, would interested to know, but powdercoat is essentially paint, it’s powder stuck to the part by static and put into an oven and melted, but very similar to paint.
I’ve not seen paint or powdercoat last on any aluminum part continuously subjected to salt water, to include aircraft.

I wonder if Jim’s dinghy may have been made from 5000 series aluminum and not the normal 2 or 6 thousand series aluminum? Perhaps it’s the aluminum and not the powdercoat, especially since the barrier has been broken?

[s/v michaela]

Aluminum needs to be blasted to clean or by using a monti tool to profile the metal. Alodine, Aluma prep, then zinc chromate, 545 primer, epoxy barrier coat, then bottom paint... It will stay on......just did mine last year. The previous coating lasted ten..

[CarlF]

You can make powder coating last a long time in salt water but it takes special pretreatment, powders, and excellent quality control. Something zodiac probably didn’t want to pay for.

But aluminum boats need anti fouling paint just as much as fiberglass boats and the marine coating manufacturers like Pettit and Interlux have designed paints and primers for the purpose. Topsides too since aluminum is a popular material for super yachts and bare aluminum isn’t “the look” they want.

If the OP is willing to spend the time to sand off the powder coating, any of these will give excellent service. Trilux-33 is one example https://www.international-yachtpaint...4_20150407.pdf