Repainting Oxidised Aluminium

I would just get some aluminum engine paint from the local auto parts store, and I would use some metal prep or acid etch primer....or for a more permanent solution I would go with por15 high temp paint...

I give redfred a GA for citing the correct, and only, method for dependably painting bare Aluminum.

During my years in the aerospace industry, we used lots of aluminum and always prepared it the way his site instructs.

Look at Alodine 1200 or similar conversion coatings.

Henkel Alodine 1200S Conversion Coating MIL-C-5541C

Absolutely correct! The poor bond is between anything attempting to bond with the very hard aluminum oxide.

You can't win them all.

Thank you for the compliment.

If your recommended procedure followed closely, the paint should adhere very well.

In a well equipped shop (and even a DIY shop looking for success) the Al piece would go directly from a water rinse after etch, while still wet, into the conversion bath.

A properly prepared and etched surface will cause the water to "sheet" or wet and cover the work piece to keep it from coming into momentary contact with any air.

There is also another, more complex and expensive method called anodizing. I do not suggest that you even consider this unless you are willing to pay to have it done.

Anodizing - Wikipedia

Pre/under coat via anodizing, followed by final painting.

As you're in UK, Hammerite does most things. I don't know offhand whether it's good for bare aluminium, but it should say on the tin.

The loose white powder indicates that the casting is not pure aluminum, but more likely a 9% or 12% zinc aluminum alloy commonly used in thin sand castings and in die castings. The grille sides are most likely die cast. and the powder is a mix of zinc oxide and aluminum oxide or also potentially zinc or aluminum hydroxide. The problem is that the zinc/aluminum oxides and hydroxides pit and tend to go through the metal rather than passivating on the surface.

You need to get the surface really clean and then mild acid etch, rinse and dry before painting or the white powder will spread under the paint. Any sort of caustic cleaner will eat the metal alive. High temp paint is a must, up to and including silicone based or epoxy high temp paint.

Thank you all for giving advice to my problem. What would seem a simple task is like Topsie - it grows and grows and grows!

I now have to decide what to do in terms of an unsatisfactory quick fix or investing in a more permanent solution. I have asked this question because the bbq belongs to my 86 year old neighbour and he wants to tidy the bbq for when his friends come to visit. I will show him these replies and then decide on the next course of action.

Again, thank you for your guidance.

Get him to buy you a sand blaster.

That may be an answer but the problem of oxides forming may still exist. Also, the cost may exceed a new bbq. The gentleman is 86 years old!

After hearing this, you may just want to wire brush, wipe and paint the thing with some high temperature paint. Two coats, at least.

That SHOULD be good for one or two seasons.

Good luck!