Finishes: mill finish, anodising and powder coating
The same profile can be silver, bronze, black or any colour. What each finish is, how long it lasts and which one suits each use.
In short
- Mill finish: the profile as it leaves the press. It is the cheapest option, but it dulls and stains over time.
- Anodising: thickens the natural oxide layer of aluminium. The result is metallic, hard and does not peel; for exteriors, a thickness of 20 microns or more is used.
- Powder coating: a coating that is melted in an oven. It allows any colour and texture, with a minimum thickness of 60 microns.
Mill finish
This is the profile without any treatment, in the silvery grey colour of the metal. Aluminium forms a very thin oxide layer on its own that protects it, so it does not "rot" like iron; but over time it dulls, develops whitish stains and shows fingerprints.
It is suitable for parts that are not visible, internal structures, and profiles that will later be machined, welded or finished elsewhere.
Anodising
It is an electrochemical process: the profile is immersed in an acid bath and an electric current is used to grow the aluminium oxide layer on purpose. That layer is part of the metal, not a coat of paint on top: it does not peel and it is very hard.
- Thickness: measured in microns (µm). The usual classes are 10, 15, 20 and 25 µm. For interiors, 10 to 15 µm is enough; for exteriors, 20 µm is recommended, and 25 µm near the sea or in industrial areas.
- Colours: natural or clear (silver), bronzes in several shades, and black. They are metallic colours, always within that range.
- Sealing: at the end, the pores of the layer are closed. Poor sealing is the most common cause of anodised finishes that stain.
The alloy matters: 6063 and 6060 are the alloys that anodise best. With other alloys the colour can come out uneven.
Powder coating ("termoesmaltado" in Argentina)
An electrostatically charged polyester powder is applied and clings to the profile. It is then melted and cured in an oven at about 180 to 200 °C. Beforehand, the profile goes through a chemical pretreatment that ensures adhesion.
- Colours: practically any colour on the RAL chart, in matt, satin or gloss, as well as textured and wood-effect finishes.
- Thickness: the minimum required by quality labels for exterior use is 60 µm.
- Weak point: a knock or a deep scratch can leave the metal exposed. It is touched up with repair paint.
Which one to choose
| Use | Recommended finish |
|---|---|
| Windows, doors and façades in catalogue colours | Powder coating |
| Windows, doors and shopfronts with a metallic look | Anodising, 20 µm or more |
| Projects near the sea or in industrial areas | 25 µm anodising, or powder coating with a quality label for aggressive environments |
| Machine parts, internal structures | Mill finish |
| Parts that are handled a lot (handles, railings) | Anodising: it resists wear better |
Maintenance: for both finishes, cleaning with water, a neutral detergent and a soft cloth once or twice a year is enough, and more often near the sea. Never use abrasive products, solvents or steel wool.
Frequently asked questions
Which is better, anodising or powder coating?
It depends on the use. Anodising is harder and does not peel, but it only comes in metallic shades. Powder coating allows any colour, although a hard knock can mark it. For exteriors, both perform well if they meet the thickness requirement: at least 20 µm of anodising or 60 µm of powder coating.
How do you clean anodised or powder-coated aluminium?
With water, a neutral detergent and a soft cloth. Do not use abrasives, solvents or steel wool.
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