Painting aluminium

Is there a specific primer for aluminium or will ordinary metal primer be ok.

Etching primers are normally used with Aluminium - these 'eat in' to the surface a bit. Ordinary primer is unlikely to stick well to the inevitable oxide layer.

Eric,

I must confess that I tend to avoid painting

I do, however, have some experience with adhesive bonding; and there are obvious similarities.

To do a "proper" job, you need to remove the layer of oxide from the Aluminium, then paint it immediately. Note: the oxide starts to re-form within minutes, so this is not a simple matter.

In the Aircraft repair business; after abrasion, they use Phosphoric Acid [which is the active ingredient of Jenolite, etc.] to micro-etch the Aluminium immediately prior to bonding.

Short answer ... Painting Aluminium is best avoided.

That said; I'm sure someone here will tell you how they do it.

MichaelG.

Eric,

Etching primer is the most satisfactory process available without industrial scale methods. These industrial process involve tanks of so-called chromating solutions operating at elevated temperatures under time control.

Much work was done by the military, especially in the US to develop a suitable method of obtaining adhesion to aluminium/aluminum at room temperature.

The eventual discovery was the 2-pack etching primer consisting of a base, yellow containing zinc chromate using polyvinyl butyral as a binder and a separate activator containing phosphoric acid. These have to be thoroughly mixed and the resulting primer applied within a few hours. The mixture reacts within itself and in about 8 hours becomes ineffective. There is no need to abrade the surface to be painted. In fact abrasion of the smooth aluminium is counter-productive as these primers have very low build.

These 2-packs provide the best adhesion as they
1 etch the surface due to the acid,
2 phosphate that surface providing a degree of protection against the re-oxidation of the aluminium and
3 also yield a surface to which the next coat of paint can adhere.

Developed from that know-how are self-etching primers, these are totally dissimilar from the 2-packs, but are simpler to use. In the sort of service which hobbyists enjoy they normally prove entirely adequate.

In the aircraft manufacturing and maintenance industries various other formulations are employed based originally on epoxies and more latterly on polyurethanes These are outside the scope of amateur use but meet the specifications for resistance to the various chemicals which are present on an aircraft. Especially resistance to hydraulic fluids.

Just for the record and to add to the fount of human knowledge on what is a most complex problem. Much is shrouded in the mysteries surrounding military applications.

JerryNotts

One of my albums is headed Workshop, in there you'll see the fuselage of a Cessna 185 freshly painted with Zinc Chromate primer, I can't remember which type of paint the aircraft ended up with(next photo), our agricultural aircraft were painted with epoxy resin to withstand the erosion from the chemicals used in aerial topdressing. The paint used by the manufacturer in the early 1960s did not last well in ag work, but this aircraft was not designed for this work.

The paint stayed stuck on, the metal is Alclad 2024-T3 with a layer of plain aluminium on both sides as basic corrosion protection. Ian S C

Blimey, all I wanted to paint was a model mill engine cylinder not a 747

If it snot going to see much use then the spray can etch is good enough, something like Acid #8 by Upol which can be bought from Halfords or on the net. If its going to be used a lot with steam then the Etch that Phoenix do has a bit more bite to it.

I used Hammerite Special Metals Primer available from Halfords and no doubt elsewhere on the aluminium castings of my Speedy recumbent trike. You can overpaint with "most paints" and clean brushes with water. My topcoat is still there.

Is there anything that I can spray on this alloy corrosion that will inhibit it?

Over the last few years I have bought 2 new cars with alloy blocks. After the first winter spray of salt, the engines were very sorry looking with all the alloy corroded. Both Ford & Rover said it did not matter-- which is the opposite to how I felt. if they had been iron blocks they would have painted them, as it is the engines look poor and neglected.

WD40 is not any use for this.

Surely there is something one can do to smarten this up?????

Ray Foster

Hi there, all,

Have a look at this web-site:

http://www.onelargeprawn.co.za/2010/02/01/flying-101-kululas-livery-is-factual-quite-funny/

Best regards,

Swarf, Mostly!

Ray, When you get a new car, strip out the engine, and get it anodised, might be cheaper to let it corrode, and buy a new engine, or maybe new car. Be like me, ride a bicycle. Ian S C

Thanks for that Ian, what a pearl of wisdom, I had not thought that I could ride my bike as the tyres are flat, which

they have been for over 65 years. Maybe one of my motorcycles would be better?

Ray Foster

When you use etch primer, let it dry properly first. We have had a few problems with high build topcoats over etch where the solvent hadn't flashed off properly, and condensed out between the etch & metal. The paint then peeled off very well.

Regards,

Richard.