Finishes
Anodising
Anodising is an electro-chemical process that thickens the natural oxide layer on aluminium, so the finish is part of the metal rather than a coat on top. BS EN ISO 7599 covers anodising generally, and BS 3987 covers external architectural use, where 25 microns is the usual film.
Where does it work well?
Metal frames, cladding and heritage-style bronze or silver aluminium on buildings where a metallic look is wanted, and the owner is happy with a narrower colour range than powder coating offers.
Pros
- Metallic appearance
- Hard surface that will not peel like paint
- Good resistance to wear
- No recoating cycle
Cons
- Limited colour range
- Batch shade variation can show
- Cannot be touched up invisibly on site
How long does it last?
Typically decades with regular cleaning, though the surface can stain or dull if neglected.
What should you check when buying?
Ask for the film thickness, with 25 microns usual for external use, and try to keep all parts in one batch to limit shade differences. Qualanod is a quality label for anodisers, so ask for evidence if you specify it.
Common questions
Can anodised aluminium be repaired?
Not invisibly. Anodising is done in a tank, so a scratch cannot be reworked on site. Light marks may clean up, but deeper damage needs a new section or a painted repair, which will look different from the metal.
Can you change the colour of anodised frames?
Yes, by painting, as long as the surface is prepared properly and a compatible primer is used. Re-anodising in place is not possible, because the parts would need to come out and go through the tank.