powder coating

[jim lee]

How well does powder coating work for keeping things from corroding? Is it better or worse than paint?

thanks!

-jim lee

Jim. I am not a paint expert but do a lot of boat work and have been around it. There are epoxy paints, Devoe products amongst them, that are amazing in preventing corrosion. I believe that powder coating is a little tougher and resists heat better, paint resists lifting better if the film is damaged and water gets under. I whittled the most beautiful engine beds imaginable out of 3/8 steel angle, powder coated, then changed my mind on mounting the engine and had to cut part of the newly coated steel. The short answer is that the metal is always coated with ACF-50 and is shiny like a new penny years later. Tho I had a mixer drip saltwater on the rail and a mounting bolt, there is no visible sign of corrosion. Powder coating is cheaper than good quality epoxy paint and there is less chance of a "holiday". Awlgrip, Imron, Sterling, etc. cannot keep up in the anti-corrosion race.

[CDK]

Powder coating looks better and is cheaper to apply.

It does little or nothing at all to protect against corrosion if it was the only treatment the product was subjected to. I've seen coating coming off in large flakes and blisters within weeks of immersion in seawater because the material under it was not thoroughly cleaned or degreased.

[TollyWally]

Paint doesn't do to well under those conditions either. What's the lowdown on a more apples to apples kind of comparison?

How does powder coating compare to high quality paint when both are applied using best practices?

[CDK]

Over light alloy, after sandblasting, etching and/or a good primer, epoxy powder coating can provide a mechanically stronger, pore free layer, superior to other paint systems. Thicker and more uniform because there are no solvents involved that cause sagging and need to evaporate.

Over steel I'm not so sure. Galvanizing or zinc dipping provides excellent resistance to corrosion but both have poor adhesion for paints except the ones containing an organic acid that bonds to the zinc. As far as I know there are no epoxy powders with such properties.

[TollyWally]

Thanks CDK,
Am I correct is assuming light alloy means aluminum? Sounds like one advantage of powdercoating over more traditional coatings might be a less permeable membrane because solvent didn't have to flash off through it?

[CDK]

Correct both times.

The stuff we call aluminum is one of many alloys containing Al, Mg, Si, Zn, Cu to name just a few, where Al is always the dominant element.

The solvent evaporates at the surface first, leaving the paint "dust dry", the deeper parts would never dry if there were no pores. With a lot of thin layers, like the paint on a car, the layer is less permeable, but never 100%.

[jim lee]

So, for aluminum parts, powder coating would probably work fine? At least as good as paint?

-jim lee

[Herman]

I once had a racing sailboat, campaigned extensively on salt water, and it had an aluminium beam in it, which was black powder coated. During the years (5 or so) I never had any problem with this beam.

[jonr]

Watch the temperatures with aluminum such that the strength isn't altered. Or use the far lower temperature UV cured powder.

[TollyWally]

A boatyard I know uses powdercoated aluminum to frame the window areas of the wheelhouses of some of the boats they build. The finish holds up well during construction and simplifies the final completion.

[jim lee]

Great thanks! I used powder coating on the compression post, base and keel stop (Top of keel) Looked wonderful and was drop dead easy and cheap to have done locally. My worry was, "Was this too easy? What am I missing here?"

Thanks for the replies!

-jim lee

[jonr]

I just powder coated a small piece of aluminum and put it in a salt water. I'll leave it there to see what happens.

Low temperature powders have the advantage that ovens can be built from foam - such as http://www.jm.com/insulation/buildin...media_2512.htm

[Cheesy]

For steel use a phosphate pretreatment, ie acid etch and a phosphate surface treatment, before powder coating the parts must be completly dry and have no rust. For the best corrosion resistance use a zinc epoxy undercoat followed by a polyester top coat. Galv or ZP steel is a bit harder but can be done just as well as (or very close to) uncoated steel, depending on the surface there are several different pretreatment methods.

[jonr]

> I just powder coated a small piece of aluminum and put it in a salt water. I'll leave it there to see what happens.

Absolutely nothing was happening (very well attached, looks good, hard to scratch) so I threw it out.