Three metal finishes look similar on a product photo and behave nothing alike after two winters in a wet room. Powder coating is paint that has been baked on; anodising converts the metal surface itself; chrome is a thin electroplated layer over something else. Knowing which one you are buying explains why a $20 rail spots at the joints in a year while a $60 one still looks new – and it tells you where to look for the first sign of failure.
1. Three finishes, three mechanisms
Powder coating sprays a dry polymer powder onto the metal and cures it in an oven at roughly 180-200 C. The result is a 60-80 micrometre film that is tough, colour-fast and slightly flexible. It sits on top of the metal, so it can chip – and once chipped, the steel underneath is exposed.
Anodising is an electrochemical process that grows an oxide layer out of the aluminium itself, typically 10-25 micrometres thick. It does not sit on the surface like paint; it is the surface. That is why anodised aluminium does not chip or peel, and why the colour is more resistant to fading in sunlight.
Chrome plating is electrodeposition: a copper layer, then nickel, then a very thin chromium layer of roughly 0.1-0.8 micrometres. The chrome is what you see and touch; the nickel underneath is what actually resists corrosion. Thin nickel equals early pitting.
2. The salt spray number
Finishes are compared with a salt spray test, measured in hours until red rust appears. A decent powder coat on prepared steel manages roughly 200-500 hours; a cheap decorative chrome on a thin nickel layer can fail in 24-72 hours. That gap is the difference between “I wipe it weekly” and “it spotted at the weld in the first month”, and it is invisible in a product photo.
3. Where each finish fails first
| Finish | Thickness | Resists | Fails first at | Typical life, wet room |
|---|---|---|---|---|
| Powder coat | 60-80 µm | Chips, UV, colour | Cut edges, screw holes, welds | 3-6 years |
| Anodised aluminium | 10-25 µm | Peeling, fading, light abrasion | Deep scratches, strong alkalis | 6-10 years |
| Chrome on steel | 0.1-0.8 µm Cr | Appearance, hardness | Pitting at joints, thin nickel | 1-3 years |
4. The edges tell you everything
Powder coating is applied as a film, and films are thinnest where geometry fights the spray: cut edges, inside corners, the rim of a screw hole. That is why cheap rails rust in a ring around the fixing rather than in the middle of a tube. When you look at a coated product, look at the edges first – a visible line of bare metal or a rough overspray is the tell.
Chrome fails differently: it pits. Small dark specks appear at joints where moisture sits, then the nickel layer goes, then the steel. By the time you see a spot, the layer beneath is already compromised, and polishing makes it worse.
5. Why aluminium changes the maths
Anodised aluminium has an advantage that has nothing to do with the finish: even if you scratch through the oxide, the metal underneath forms its own thin oxide layer and does not rust through. It may look worn, but it will not bleed orange streaks down a tiled wall – which is the failure people actually notice.
It is also lighter: aluminium is about 2.70 g/cm3 against steel at 7.9. A hollow aluminium caddy can weigh under 500 g where a coated steel equivalent is 900 g or more, which matters both for the mount and for shipping.
6. What to check in a shop or on a listing
- Look for the finish name, not the colour: “powder coated”, “anodised”, “chrome plated”. Vague “rust-proof” means nothing.
- Inspect the edges and screw holes for bare metal or rust rings.
- Weigh it in your hand: a steel rail that feels light usually means thin walls and a thin coating.
- Check the joints – welds, sleeves and hinges are where coatings break first.
- Compare price against finish: a chrome rail at a third of the price of a coated one is usually thin nickel.
7. Maintenance that actually extends life
Wipe, do not scrub. Abrasive pads remove the top layer of any finish; acidic descalers attack chrome and anodised surfaces; chlorine-based sprays attack everything. A damp cloth weekly and a full dry after showering is enough. For coated steel, touch up chips early with a matching paint pen – a 1 mm chip left alone becomes a 10 mm rust bloom in a wet room within a season.
8. The cheapest mistake
Buying a decorative finish for a wet room. Chrome belongs where it stays dry; powder coat is fine where it is not scratched; anodised aluminium and good stainless belong in the shower. The price difference between the right finish and the wrong one is usually smaller than replacing the wrong one twice.
9. Stainless steel is a finish argument too
304 stainless is not a coating at all – it is an alloy with roughly 18% chromium and 8% nickel, and its corrosion resistance comes from a passive oxide layer that reforms when scratched. That is why a brushed 304 rail survives where a chrome-plated one pits: there is no thin decorative layer to breach. Grade 201 substitutes manganese for part of the nickel and costs less; it also spots sooner in a wet room, which is why a suspiciously cheap “stainless” caddy is usually 201.
The practical test is a grade stamp plus a magnet plus a price sanity check. 304 is usually non-magnetic but can become slightly magnetic when cold-worked, so a magnet alone proves nothing either way.
10. The five-year cost of the wrong finish
Compare two rails: a $20 chrome-plated one that pits at the joints after 18 months, and a $60 anodised aluminium one that lasts six years. Per year, that is $13.30 against $10 – and the cheap one fails at the least convenient moment, usually mid-shower, with a shelf of bottles coming down. Add the replacement delivery window (7-15 days to the US, 10-20 to the UK, Canada and Australia) and the “cheap” option costs a fortnight without a working rail as well.
That is the whole case for reading the finish line instead of the price tag: the number that matters is cost per year in service, and the finish is what sets the service life.
Frequently asked questions
Is powder coating better than paint?
Yes for metal in wet rooms: it is thicker (60-80 µm), cured harder and more chip-resistant than wet paint. It still fails at cut edges and screw holes, where the film is thinnest.
Does anodised aluminium rust?
No – aluminium does not contain iron, so it cannot rust. It can corrode in strong alkalis or salt, but it forms its own oxide layer and will not bleed orange stains.
Why does cheap chrome pit so quickly?
Because the nickel layer under the chrome is thin. Chrome is only 0.1-0.8 µm; the corrosion resistance comes from nickel, and decorative plating often skimps on it.
What does the salt spray rating mean?
Hours in a salt fog before red rust appears. Good powder coat on prepared steel: roughly 200-500 hours. Thin decorative chrome: 24-72 hours.
Can I repair a chipped powder coat?
Yes, with a matching touch-up pen. Clean and dry the chip first, then seal it – an exposed edge in a wet room spreads rust quickly.
Honest disclosure: thicknesses and salt-spray ranges are typical values for these finishes, not a guarantee for a specific product.
Gear referenced in this guide
Aluminium Hanging Shower Caddy, Double Basket
Hollow aluminium, slot drainage: the finish argument in section 5, in a wet room.
$63.99
Rotatable Corner Bathroom Organizer, Wall-Mounted
Injection-moulded PP – no coating to chip, which is its own answer to the problem.
$54.99
Compare on Amazon — this category usually has more brands, sizes and price points there.
Check current prices on Amazon →
As an Amazon Associate we earn from qualifying purchases. The price you pay is unchanged. Disclosure