Painting Aluminium Question?

[Mark Jones]

Do I need to use etch primer on anodised aluminium ?
The job is a shower door
My friend has a gold anodised door ..
he wants it white now.
thanks in advance ....all the best....mark

[Evan]

Bit of a problem. The best thing to etch anodized aluminum is a lye solution but it will also etch glass. This would be considered a severe duty application so you want it to stick. One possibility would be to completely mask the glass panel on both sides and fine grit blast the aluminum, clean thoroughly with a degreaser like alcohol then use a 2 part epoxy paint.

[Mark Jones]

Thanks Evan I was going to use two pack paint..
The etch I was going to use contains phosphoric acid .....I know bare aluminium can be etched with this stuff ...was wondering how it would perform on anodised.
my Fiend is emergrating to Australia .(LUCKY SOD)..and he needs to sell his house in a hurry......so if the job only lasts,say two years before it starts pealing off...he would be happy....IT'S JUST A MAKE-OVER.
...not the way I would go ......but if he's happy I am.
Going down this route would cost him about £20.......the proper way would be to buy another door .......but he wont do this.
all the best.....mark

[Milacron of PM]

You don't need to etch anodized alumium as the anodizing process itself is a form of "etching" and presents a neutral surface ideal for painting over.

As to non anodized aluminum, chemical etching is tricky business, if you apply too much the chemical will inhibit drying of the paint (I've had Sherwin Williams Polane go from normal drying time of 15 minutes to 15 *hours* due to this) and if you don't apply enough the etch effect won't be deep enough to do much good.

Better in my experience is abrasion with 3M Roloc pads and die grinder and then thorough cleaning with the same solvent present in the paint you will use. i.e. don't use laquer thinner to clean if you then apply poly or epoxy type paints...in this case laquer residue will increase drying time and reduce paint hardness dramatically.

Clean with white rags/solvent until very little "black" shows on the rags and then paint within an hour or so (otherwise the surface will reoxidize and need to be cleaned yet again)

[Evan]

I beg to differ Don. Anodized aluminum is often treated with various sealing agents including PTFE, Silicone, Potassium Dichromate, and even Lanolin. None of these will make for good paint adhesion. IF the surface has been sealed with a boiling water only seal then it will accept paint well. That is not usually the case with commercial anodizing. I recommend an etch, preferably one that removes the anodizing. Perhaps you are thinking of alodining which is a different process that produces an excellent paint ready surface on aluminum.

[Mark Jones]

Thanks guys.
I'm going to be painting it today.
hope it turns out well.
all the best...mark

[spope14]

Hey, leave it anodized, never wash the aluminum shower door frame, and eventually it will turn white fom soap scum.

In all seriousness, I have some annodized aluminum items in my kitchen that my wife ante painred blue a few years back (baby blue, yuk). Each year I paint them again. No matter the chemical, the treatment,the wire brushing, whatever....the paint scratches off.

My best luck, two years old now, was to use an epoxy paint mix prepped at an auto paint store (friend of mine, mixed a pint). Prime it up appropriatly with the recommended primer, then did a brush coat - did not have a sprayer.

have you also checked around for that "powdered paint" that is applied electrically charged? some towns / cities have companies that do this on a piece deal.

[crossthreaded]

The June 28 issue of Aviation Week has a small article about a "non-toxic" painting prep called "PreKote." It is "basically a mixture of akali spoap and a saline compound that promotes paint adhesion." It's new & put out by the Pantheon Chemical Co. for miltary use; in this case painting F-16's &A-10's. It replaces alodynepreparation to make the paint stick. It supposedly solves problems in worker exposure of dangerous chemicals & water contamination.

[Evan]

Not intended for use on an anodized surface. That is for use on bare aluminum and yes, alodyning is a problem since it uses chromic acid (toxic).