Rust on shower door frame

The white powder is the aluminium oxidising and the 'dents' are the symptoms of corrosion. Rub it down with some sandpaper, apply etch primer or specific aluminium primer and paint. Due to the way aluminium oxidises, its difficult for paint to adhere to its surface so the correct primer is important to prevent the top coat flaking off.

 

Aluminium is a weird metal - one of the fastest corroding.

The bizarre thing about it is it's that white oxide that usually seals the metal surface and prevents further corrosion. If something is done to prevent that oxide from forming a hard skin (like the old 'mercury' experiment...), then your whole shower door would turn into a pile of white dust on your floor within the hour. Really.

There seems to be some surface chemicals on your bare metal door that is now preventing the oxide layer from forming a skin, so it's corroding away in patches, forming that white oxide powder.

CGN has the solution. Clean it all down really well - perhaps even use a wire brush too to make sure these pits are cleaned out from whatever chemical is in there (probably just shampoo or summat!), make sure it's 100% dry and use an etch primer as CGN says. Make sure it's made for this job.

You can do this easily with aerosols - just hold a section of card behind the frame to catch over-spray, and fire a good layer of primer down the surface. Make sure you have covered every speck and pit and groove. Add a few layers. You can use a 'dusting' layer to start off if you want, but subsequent coats should 'flow' and fully seal the surface. You ain't too bothered about finish, so if there's a 'run' don't worry.

Allow to fully dry, and then top-coat with a high quality spray paint. I dunno - I'm guessing that 'appliance white' stuff is durable?

 

I think you now know why that product is discontiued, too much acid, im betting thats whats attacked the alloy.
Cilic Bang is the same, it even says on the bottle not to be used on alloy.

 

Blimey.

I'm guessing that traces of that stuff are still sitting in these pits preventing the oxide skin from reforming.

It should be quite curable, TapsDIY, but DO get the surface really, really clean before priming.

 

You ain't got rust, man - you got ali oxide .

(Rust is for ferrous metals - steel, iron...)

If you read the instructions for Hammerite, it says; "On bare zinc, aluminium and galvanised surfaces, apply Hammerite Special Metals Primer before applying Hammerite Direct to Rust Metal Paint."

Hammerite is ok stuff, but it does have issues such as re-coats needing to be carried out within a certain period of time (or perhaps that's just the 'hammered' stuff?)

Whatever you use, I suspect it'll need separate primers and top-coats. But be sure to use a primer designed for 'non-ferrous' metals. And I think an 'etch' type would be wise.

 

The primer used to be zinc chromate based, Alochrome ? but now probably banned under HSE regs.

 

I'm not saying this is the best way to tackle it, but I think what I would do is to simply buy an aerosol of etch primer and a similar can of 'appliance white' paint (which I think is meant to be more durable stuff than yer average white spray paint).

Check compatibility betwixt them first, tho'.

Then use a small wire brush to clean the surface really well - especially to get into these pits. Mask off surrounding areas, and start to build up coats of the etch primer. These coats need to be heavy enough to flow into all these pits - if you apply them too lightly they might not do this, leaving pin-holes in the primer. Obviously, too-thick coats will run...

Repeat process with top coat.

There are lots of well-regarded brands of 'speciality' paints out there - Rustoleum and Plastikote for two. You'll simply have to do your research on these and others to figure out which will do this job for you best.

Keep us posted, please, on how it goes.

 

Cooool

 

Don't worry about trying to sell ones made by Hormel, Spam tends to fail when wet and become a slimy mess. Anyway, the OPs doors will have totally rotted by now and he will have possibly sourced replacements from a reputable supplier.