Anodised aluminium looks great … until it all starts to go wrong. Anodising is a very standard protective treatment used on aluminium/alloy motorbike parts, but when corrosion sets in it’s difficult to deal with.
You can’t just polish it out like you would with bare aluminium, and you can’t touch it up either. You have a handful of choices: strip it back and resign yourself to perennial polishing duties; get it sandblasted and powdercoated; or paint over it.
I decided to strip the anodising and either restore a “brushed aluminium” finish protected with hard-wearing two-pack (2K) lacquer; or give it a coat of basecoat metallic paint, once again protected with 2K.
So, why didn’t I go for powdercoating? Well, I can’t powdercoat myself, so I’d be putting myself completely in the hands of someone else and paying them for a finish that ultimately I might not be happy with. Also, the colour choices are limited, and although powdercoating is hard-wearing it isn’t straightforward to touch up if you get stone chips or other damage.
And what about re-anodising? The problem you’ve got with the subframe I’m restoring is that there are cast aluminium bits welded to regular extruded aluminium, and they have been treated separately before being joined together. So anodising them as one component could give an unpredictable finish.
The first step is to get rid of the anodising, and the simplest way is to hit it with a caustic oven cleaner. Caustic soda reacts fairly aggressively with aluminium, and oven cleaner is a relatively mild form of caustic. Just strong enough to break down the coating and let you get at the metal underneath. You can buy pure caustic, but setting up a bath for a larger component means mixing up a lot of it and the reaction can run away with itself, permanently damaging your job.
After 10 minutes or so you can hose off the oven cleaner, let it dry and see the results, which will probably be quite disgusting. The surface, if anodised, will probably go a chalky white; if it’s bare aluminium it might even go black and give you the fright of your life.
After anodising, for this kind of box section construction the best way to strip off the formerly anodised layer turned out to be a flap wheel. Watch the video to find out about what it looks like and how to use it.
Without giving too much away: I went the repainting route. Have a look at the video and you’ll find out all about the method for stripping anodised aluminium, then applying etch primer, base coat and two-pack or “2k” lacquer. Safety warnings apply when using 2k – it is a hazardous material and you need to protect your lungs with the right breathing equipment.