Polishing Aluminium

[john thompson]

Have a fifty year old or so aluminium lamp housing that has been sprayed black. The black paint is bubbling off in places and we wish to restore it to a nice aluminium finish. Not neccesarily a shiny finish, a matt one would be just fine; and probably easier.

Using wet and dry carborundum paper is going to be quite a big job to get it looking good, especially around the detailed parts of it.

Is it possible to buy a small fairly inexpensive 'sand blaster' that would do the job? Or even some kind of paint stripper, either of which would not damage the aluminium surface?

Grateful for advice on how you might tackle this job.

[Sla#s]

Have to do this every day - (Aircraft engineer)

1. Remove paint. (paint stripper)
2. Remove worst of corrosion mechanically. (wet n dry and gentle fine wire brush. NOT a brass one)
3. Kill corrosion - use Phosphoric acid (Jenolite). Wet for 5 min then wash off with water. Dry thoroughly.
4. If you are going to paint it you can prep surface with something like Alodine - it's a bit like anodising. (Not sure of how to get that other than commercially)
5. Polish or repaint. If painting use "Self Etching Primer" for first coat.
6. For polishing Google "polishing aluminium".

Good Luck Slatts

[The Natural Philosopher]

On alumimium?

Surely not!

[Sla#s]

But yes! It must be washed off with water after about 3/5 min and then dried though.

I don't have FAA AC 13.43. 1B (The engineers bible) with me but could look up the ref if you want...? This produces an excellent surface for anodising or painting.

There are other acids one can use but phosphoric is the easiest to optain.

Slatts

[The Natural Philosopher]

But not for POLISHING?

[Windmill]

Baking soda etches aluminium.

[Steve Firth]

I'm glad I wasn't the only one thinking that.

My experience with polishing aluminium is that it's a waste of time. After a few days it's back to dull again. Getting a good polish is possible by using "Bar Keepers Friend". This is a feldspar abrasive that uses a rotted feldspar that breaks down during polishing into finer and finer particles. It's possible to get a mirror like polish using a damp cloth, bar keepers friend and elbow grease.

There are other similar abrasive compounds but BKF does the job and is cheap.

[Tim Streater]

Can aluminium be shiny? Once exposed to the air, it immediately oxidises, and at least with ally the oxide is hard and doesn't flake off (unlike iron). I would have assumed that the oxide would look dull or matt though.

[Steve Firth]

[snip]

It can be shiny for a time. I think the oxide layer is transparent when it is thin. IASTR that the white coating on aluminium when it is exposed to rain is in part aluminium carbonate, not the pure oxide.

[Tim Streater]

Ah, righto. The carbonate deffo looks grotty.