Powder coating and anodising both protect aluminium and change how it looks, but they work in very different ways. Powder coating adds a coloured layer on top of the metal. Anodising grows a harder oxide layer out of the metal itself.
Which one suits your project depends on the colour you need, where the aluminium will be installed, how much it will be handled and how it will be looked after. Altus® Industrial Aluminium offers mill finish, powder coated and anodised material, so the finish can be matched to the job. Powder coated and anodised material is supplied mill direct, in mill run quantities of 150 kg and over.
How powder coating works
Powder coating is a dry paint. A fine powder is sprayed onto clean, pre-treated aluminium with an electrostatic charge, so it clings evenly to the surface. The part then goes through an oven, where the powder melts and cures into a tough, continuous film.
Because the coating sits on top of the aluminium, it brings three practical advantages:
- Colour choice. Almost any colour, gloss level or texture, including matches to building schemes and brand colours.
- Repairability. Minor damage can be touched up, and a tired finish can be recoated.
- Performance grades. Powders come in different durability grades, so the finish can be matched to the site.
Altus Industrial works with Dulux powders, including Duralloy® +PLUS for everyday architectural use, Dulux Duratec® for coastal and high-UV sites, and Dulux Protexture® for a textured, scuff-resistant finish.
How anodising works
Anodising is an electrochemical process. The aluminium goes into an acid bath, and an electric current thickens the thin oxide layer that forms on aluminium naturally. The new layer is part of the metal, so it cannot peel or flake the way a coating can.
Anodised aluminium keeps its metallic look. It is worth noting that anodising is available in a range of colours, although New Zealand’s main anodising suppliers have standardised on silver/natural, bronze, and black finishes. Smaller specialist anodising plants offer a wider range of colours, generally at a higher cost. In Australia and New Zealand, architectural anodising is graded by coating thickness in microns under AS 1231, with thicker grades used for harsher environments.
Anodising adds far less thickness than powder coating, which suits close-tolerance parts. Scratches through the anodised layer cannot be invisibly repaired, and colour can vary slightly between batches, so it pays to finish a whole job in one run.
Side by side
| Powder coating | Anodising | |
|---|---|---|
| Appearance | Solid colour, any gloss or texture | Metallic, the aluminium shows through |
| Colour range | Very wide, including custom matches | Mainly silver/natural, bronze and black; more from specialist plants |
| How it protects | A cured film bonded to the surface | A hardened oxide layer, part of the metal |
| Scratches | Softer, scratches more easily | Very hard, resists scratching and abrasion |
| Knocks | Thicker film absorbs impact | Thin layer can crack if hit hard or bent |
| Strong sun | Colour and gloss fade slowly; higher grades last longer | Satin etch anodising is very UV stable |
| Repairs | Can be touched up on site | Hard to repair; badly damaged parts may need replacing |
| Added thickness | More | Much less |
Which finish suits your project?
Choose powder coating when the colour has to match a building, fleet or brand, when you want a textured or low-gloss look, or when you may want to repair or refresh the finish later.
Choose anodising when you want the look of metal rather than paint, when parts will be handled a lot (handles, trims, signage), or when dimensions are tight.
Choose mill finish when the aluminium will be hidden, or will be fabricated further before it is finished.
Matte black or a metallic look?
A matte or low-gloss black is one of the most requested architectural colours, and powder coating gives the widest choice of blacks, gloss levels and textures. Anodising can also be black, but it keeps a metallic lustre: you see the metal through the finish rather than a flat colour.
If the job mixes anodised parts from different batches, ask for them to be finished in one run, because anodised colour can vary slightly from batch to batch.
Coastal, geothermal and high-UV sites
NZS 3604 sorts New Zealand building sites into exposure zones by how much wind-driven sea salt they get: zone B (low, inland), zone C (medium) and zone D (high, coastal). Zone D covers everything within 500 m of the coast, and geothermal areas such as Rotorua are treated as corrosive microclimates of their own.
Auckland, Wellington and Christchurch sit entirely in zones C and D, so most jobs need a finish chosen with salt in mind. On these sites the grade matters as much as the process. For powder coating near the coast, the Dulux warranty requires Dulux Duratec®. For anodising, it means a thicker coating grade. BRANZ explains the zones and how to find a site's zone.
Check the project specification. On architectural projects, the specification (for example a Masterspec clause) usually sets the finish and grade for the site's exposure. Send it to the team with your order so the finish matches what was specified.
Tell the team where the job is going before you order.
Why does old powder-coated aluminium look chalky?
Strong sun slowly breaks down the surface of a powder coat. Over the years the colour fades and a fine, powdery film can form on the surface: this is called chalking. Higher-durability powders hold their colour and gloss for longer, and regular washing slows the process.
Satin etch anodising has no paint layer to fade or chalk, which is why it is so UV stable, although some dyed anodised colours can fade in strong sun. A powder coat that has chalked badly can be stripped and recoated.
Duralloy® or Duralloy® +PLUS: ask which powder is specified
Two Dulux powders with similar names suit different sites. Dulux Duralloy® is a proven, durable powder for general interiors and mild exterior conditions. Duralloy® +PLUS is the more durable of the two and the preferred standard powder at Altus Industrial. It suits most New Zealand conditions, though not every site: near the coast, the Dulux warranty requires Dulux Duratec®.
Two powder-coated finishes can look the same on the day they are installed but use different powders. Ask which powder is specified, and tell the team where the job is going, because the site decides which powder is suitable and covered by warranty.*
*Dulux Alumi Shield™ warranties apply when the powder is applied by a Dulux Accredited or Prime Accredited Powder Coater to the warranty specification, on recommended project types and conditions. Altus Industrial is a Dulux Prime Accredited Powder Coater. See Dulux Alumi Shield™ warranties.
How to tell if aluminium is anodised or powder coated
If you are replacing or matching existing joinery, it helps to know which finish you have. These are signs to look for, not a laboratory test:
- Feel. Anodised aluminium feels smooth and hard, like bare metal. A powder coat feels like a thicker painted layer.
- Look. Anodising keeps a metallic sheen, even in bronze or black. Powder coat usually looks like a solid, even colour.
- Chips and scratches. A chip in powder coat shows a layer of colour over bare metal. Anodising has no separate layer to chip off.
- Age. An older powder coat that has been in strong sun may leave a chalky residue on your finger. Anodising does not chalk.
If you are still unsure, send the team a photo or a sample and they will help you match it.
Cost and batch size
The price depends on the finish, the powder or anodising grade, and how much you are finishing. Both are batch processes, so small custom runs cost more per piece than large ones. Send the team your quantities and finish for a firm price.
Looking after the finish
Both finishes last longest when they are cleaned regularly: wipe with a wet cloth and mild soapy water, then dry with a dry cloth. Cleaning removes salt, dirt and pollutants before they can attack the surface. Sites near the sea, and sheltered areas the rain does not reach, need cleaning more often.
A dull anodised surface can often be cleaned back to its original look. A powder coat that has broken down cannot be restored that way; it has to be stripped and recoated. Coating warranties usually depend on regular cleaning, so check the care conditions for your finish.
Repairing scratches and damage
Minor damage to a powder coat can be touched up on site, and a tired finish can be recoated. Anodising cannot be invisibly repaired, so a badly damaged anodised part may need replacing. If a part will be handled or knocked a lot, factor that into the choice of finish.
Talk to Altus Industrial
Altus Industrial Aluminium supplies extrusions, sheet and plate with fast nationwide delivery available anywhere in the country. Powder coated and anodised material is supplied mill direct, in mill run quantities of 150 kg and over. Contact the team with your drawings, location and colour, and they will help you choose the right finish. See all services, or read why aluminium cutting matters.
Frequently asked questions
Is powder coating cheaper than anodising?
It depends on the finish, the grade and the size of the run. Both are batch processes, so small runs cost more per piece. Ask the team for a price on your job.
Which finish lasts best near the sea or in geothermal areas?
Both can last well in exposure zone D and geothermal areas when the right grade is chosen and the surface is cleaned regularly. For powder coating near the coast, the Dulux warranty requires Dulux Duratec®. For anodising, it means a thicker coating grade.
What is the difference between Duralloy® and Duralloy® +PLUS?
Duralloy® +PLUS is the more durable Dulux powder and suits most New Zealand conditions. Standard Duralloy® suits general interiors and mild exterior conditions. Near the coast, the Dulux warranty requires Dulux Duratec®, so ask which powder suits your site.
How can I tell if my windows are anodised or powder coated?
Anodised aluminium feels smooth and hard like bare metal and keeps a metallic sheen. Powder coat feels like a thicker painted layer, a chip shows colour over bare metal, and an old powder coat may leave a chalky residue. The team can help match a photo or sample.
Why does my powder-coated aluminium look chalky?
Years of strong sun break down the surface of a powder coat, leaving a fine, powdery film. Higher-durability powders and regular cleaning slow it down, and a badly chalked finish can be recoated.
Can I get a matte black finish?
Yes. Powder coating gives the widest choice of matte and low-gloss blacks and textures. Black anodising is also available, with a metallic look.
Does anodised or powder-coated aluminium fade in the sun?
Satin etch anodising is very UV stable, because there is no paint to fade. Powder coatings slowly lose colour and gloss in strong sun, and higher-durability powders hold them for longer.
Which is tougher, anodising or powder coating?
Anodising is harder and resists scratching and abrasion. Powder coating is softer, but its thicker film absorbs knocks better, while an anodised layer can crack if the part is hit hard or bent.
Can a damaged finish be repaired on site?
Powder coating can be touched up on site. Anodising cannot be invisibly repaired, so a badly damaged anodised part may need replacing.
