Where the
world gathers for metal finishing
Q&As since 1989




-----

Stripping and painting powder coated aluminum on a boat

January 13, 2011

I have a 1986 Mako 17' center console boat that has a T-top, a leaning post, and a poling platform that were all powder coated white more than 10 years ago. The powder coating has started flaking off pretty badly in some areas. Since I've been doing some hull repairs, I removed the T-top and leaning post and began my attempts to strip the paint so I could repaint. The aluminum in some places is gray, in other places it is shiny silver color.

What is the best way to strip powder coated paint off of aluminum and how can I repaint these. I'm trying to work within a budget, so I'd like to do this at home. I know I could take it to someone to sandblast and to someone else to re-paint, but is this do-able at home for the average Mr. Fix-it?

Dan Thompson
boat owner - Titusville, Florida, USA

---

January 29, 2011

Dan,

10 years isn't too bad performance for a marine application like this, but with flaking its time to replace the coating and regain protection for the aluminium.
The colour difference you're seeing after powder flaking is due to the oxidation state of the Al. If the newly flaked powder was well adhered, and only detached recently you should see bright shiny Al. If the flake had been loose a while, with sea water seeping under neath, then that Al will be dull. This is natural, and no real cause for concern.
Unprotected Al will eventually corrode especially if abraded in some way. It will form an oxide skin which helps to protect itself, but if you remove that fresh Al is exposed. This is similar to the body. If you pick off a scab where a wound has coagulated blood forming a scab, then fresh bood flows. The scab protects the underneath.

Removal of well adhered powder isn't easy. It should not be easy. If it were, then you have an inferior coating.
Shotblasting with Al underneath needs care. Using chilled iron grit for example can erode the metal very quickly.
But there are several products of liquid paint removers that work. One type has a methylene compound that soften the coating so that it can be brushed of scraped off easily. Try a paintshop or similar. Beware that removers for ordinary paint will not all work.

After cleaning, you could take the detached parts to a powdercoater for recoating. Ensure you get one that has a competent pretreatment system.
Otherwise, there are liquid paint systems available. You'll need several coats system that will start with an etch primer. Consult a paint sales. Beware single coat systems.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

---

February 3, 2011

I do not think this is a home handyman job.
I would be very wary of abrasive blasting salt corroded Al with the intention of re-powdercoat.
What tends to occur is that the salt is carried further into the soft Al metal.
Most chemical powdercoat strippers are derivatives of KOH in a solvent, more often than not Methyl Alcohol with stabilisers added.
This is not a good "witches brew" to self concoct as there is a violent exothermic reaction involved in the mixing.
I would think long and hard about this re-claim project but certainly give up any idea of a handyman solution.
Perhaps a mild abrasive blast with an etch prime, an epoxy primer and a two pack polyurethane finish would be better than any attempt to re-powdercoat.
This advice comes from some-one who has 30 years of Powdercoat experience and encountered several extremely frustrating and expensive failed salt encrusted Al projects in that time.
Hope this helps.
Regards,
Bill

William Doherty
Trainer - Salamander Bay, Australia