by Natalie Edwards

Want to get your aluminium fabrication to a mirror finish? While there are multiple ways of polishing aluminium to a mirror finish, these are some tried and true steps to seeing your reflection in the finished product...

Step 1: Cleaning

The first thing you'll need to do is thoroughly clean down your fabrication. If it is not new aluminium make sure any dirt, grime, paint, oil, grease or any other foreign substances are completely removed from the surface. This is important as the presence of these substances can effect the results of the next steps and lead to imperfections in your aluminium mirror finish.

Step 2: Sanding

Your second step is to sand smooth any fabrication steps you don't want to show in your finish. These could be welds, fold marks and other imperfections on the surface of the aluminium. Use a fibre disc with a top coat like Bora9 for removing welds or where high stock removal is needed, and SA331 sanding discs for light sanding and final high finishing. You will want to start with a coarse grit, gradually progressing to a fine grit and ensuring all scratches from the previous grit are removed before refining your grit. It is essential you keep your work very clean. Any grit marks left over from the previous sanding marks will need to be removed or it will show up later when final polishing, which can undo all your work.

Choosing your grits

Your starting grit will depend on the amount of metal requiring removal on the surface. For fabrications which require weld removal or have high levels of pitting to be removed, you may want to go as low as 120 grit. It is not generally recommend to use a grit any lower than this for aluminium as it can cause damage and create further work. For most fabrications you should be able to start with a 240 grit progressing to a 400, then 600 and finally to a 800 grit before moving to polishing.

Sanding Stage Product Grit/Type 
1 - Removing welds or high stock removal  Bora9 Fibre Disc    P120
2 - Light sanding to final finishing.   SA331 sanding discs    P240
P400
P600
P800 

Step 3: Polishing

Buffing aluminium to a mirror finish you will need a polishing mop and compound. For aluminium it is important not to heat the metal too much as this will cause it to harden, making it difficult to finish. Treated or natural Coolair polishing mops are made with unique layers which allow air to circulate through the folds, reducing heat build up to keep the aluminium cool.

  • Treated Coolair Mop - stiffer with less flex for more removal. Use if there are still defects on the surface which need removing.
  • Non-treated/Natural - this mop is softer to provide a higher level of finish, but less removal. You will need to have a more precise finish from sanding to use this mop.

You'll also need to choose the right compound to achieve the highest shine and mirror finish. The compound used can depend on if you are using a treated or natural polishing mop. Compounds should never be mixed on mops. Always use a new mop with a new compound.

  • Maxicut Bar - best used with a treated mop, the Maxicut is one of the fastest cutting compounds on all metal from soft aluminium to stainless steel. This compound will allow you to buff out small marks while polishing to a bright and shiny finish.
  • Tripoli Bar - for use with treated or natural polishing mops. The Tripoli provides slower cutting than the Maxicut, but a higher finish.
  • 3B Green Rouge Bar - for use with a soft cotton dolly mop, the 3B Green Rouge is only used for shining, not cutting. This will provide an extremely bright, deep mirror finish.

Using your grinder/polisher, work from the bottom of the fabrication up. Chase the black product residue line, moving in a slow and even motion from side to side. Keep moving at all times as pausing during polishing can rub in a visible defect.

Note: Be careful when polishing around the edges of your work as the polishing mop can catch the edge of the work and send it flying to the ground. You can place a spongy mat under your work to help prevent this from happening. Also try to avoid working to the edges by flipping your work around and buffing from the other direction where possible.

Polishing Stage Product Grit/Type
3 - Polishing to obtain a mirror finish Coolair Polishing Mop +
Polishing Compound 
Treated or Non-Treated Mop
Maxicut or Tripoli Compounds
4 - Polishing for extemely bright, deep
mirror finish with no defects (optional)
Cotton Dolly Polishing Mop +
Polishing Compound 
Swansdown Dolly Mop
3B Green Rouge Compound