There are a few good guides to be found online about polishing aluminium, many of them about bringing old engine parts to a high shine. The lustre of aluminium is one of the key qualities which makes it a popular choice of material for cladding on buildings and other aesthetic applications, so here is our general purpose guide to polishing aluminium.
If the surface of the aluminium has burrs or cast marks, remove these with a file. A file will leave deep and very visible scratch marks on the surface of the metal but these will be polished out later as the rest of the aluminium is cleaned up. Aluminium is a relatively soft metal, so it shouldn’t take too much effort to level off the surface so you can move on to the next step.
A coarse grit sandpaper can be used to remove heavy amount of corrosion, dirt and to level out the surface even further. This is likely the most time consuming part of the process, but taking the time to smoothen the surface of the material will only improve the finished result. Don’t forget to wear a dust mask!
Top Tip: Use a cork block with the sandpaper – it has a little bit of give that will make working on rounded edges far easier.
The next two stages of sanding should be done with 220 grit and 400 grit sandpaper. The finest grit paper will fill up with aluminium dust very quickly, and it is the finest grit you will be able to use for dry sanding.
When wet sanding aluminium – with 1200 grit sandpaper and finer – get a bucket of warm water to soak the paper in. This process can be done by hand to make sure the paper reaches any tight corners or awkward areas of the aluminium you are polishing.
Two more stages of sanding – with 1200 grit and 2500 grit sandpaper – will leave the aluminium with a very good shine, with no trace of corrosion, casting seams, filing marks or significant abrasions. If the aluminium you are working on needs to be polished to a high mirror shine – for example, if it is an engine part for a motorbike – this can be achieved with a cloth polishing disc and a good polishing paste.
A once-over with paste on a polishing disc drill bit will leave the surface of the aluminium mirrored to a high shine.
And there it is, with a little elbow grease and a good supply of sandpaper, it is easy to get even the oldest and most corroded aluminium back to a high shine and looking brand new!