Wayback snapshots show the stainless domain advertising galvanised, then pointing at sister sites for aluminium and glass. That mix is still how Australian sheds are specified: a 316 rail, a galvanised lintel, an aluminium window, and a pile of incompatible swarf.
Choose the metal for the duty, not for the adjective “premium.” This journal is an editorial desk, not a merchant. It will not quote a live price and it will not pretend one metal wins every postcode.
If the decision is already “stainless,” the alloy page is 304 versus 316. If the decision is still “which metal,” stay here.
Three systems, not three finishes
Stainless, galvanised steel and aluminium are different corrosion systems. They are not three colours of the same sheet.
| Metal | How it resists corrosion | Typical Australian duty | Weakness | Contact caution |
|---|---|---|---|---|
| Stainless (304 / 316) | Chromium-oxide film; no sacrificial coat | Kitchens, food plant, visible architecture, coastal rails in 316 | Wrong alloy, poor finish, crevices, chlorides | Carbon-steel swarf rusts on the face |
| Galvanised steel | Zinc coating eaten first | Inland roofs, lintels, budget frames | Cut edges, ground-off zinc, food faces | Zinc and stainless can fuss in wet crevices |
| Aluminium | Its own oxide film; light | Windows, cladding, weight-sensitive work | Softness, some coastal alloys, alkaline attack | Pits around stainless or copper in salt water |
A zinc rail painted silver is not stainless. A mill 2B stainless liner is not a window section. An aluminium tread plate is not a hygiene bench. The old shop family sold all three because trades buy mixed jobs. The journal keeps the comparison so the mix is deliberate.
Stainless
Chromium-oxide film, no sacrificial coating to wear through. Right alloy and finish: long life in kitchens, food plant, architecture. Wrong alloy: tea staining and pitting. Heavier than aluminium, more expensive than galvanised as a rule of thumb — this page will not invent a price.
304 is the indoor austenitic. 316 is the coastal default, not seawater armour. Finish is a separate line: mill 2B, brushed No. 4, BA, No. 8. The decoder is finishes explained. Brushed versus polished is the kitchen argument.
Sheet sizes are the Australian metric parents: typically 2400 × 1200, with 3000 × 1500 and 3600 × 1500 depending on thickness, grade and finish. See sheet sizes and the thickness chart. Custom blanks come off those parents with a historic ±2 mm shear habit — custom-cut.
Stainless is the food face, the hygiene face, and the handrail a client will touch. It is not automatically the lintel, the stud, or the cheapest outdoor frame.
Galvanised steel
Carbon steel with a zinc coating that is meant to be eaten first. Honest outdoors inland, in roofs, in lintels, in budget frames. Poor as a food face. Poor once you grind the zinc off and leave a rust line.
Cut edges and drilled holes need thought. The zinc is thin. A saw cut, a punched hole, or a ground notch is a place the coating is gone. Inland, that can be acceptable if the design allows the zinc around it to keep sacrificing. Coastal, it is a brown edge with a schedule.
Do not tell a client it is “like stainless but cheaper.” It is a different system. Galvanised wants paint or acceptance of dulling. Stainless wants the right alloy and a wash. Mixing the language is how a zinc rail ends up specified as “marine.”
Fabrication habits differ. A guillotine that just cut galvanised will throw zinc-rich, carbon-rich swarf. If the next blank is 316 No. 4, clean the machine. Cutting stainless on site is written for the stainless face; the same swarf story applies in a mixed shed.
Aluminium
Light, often a window and cladding metal, oxide film of its own. Soft compared with steel. It dents, it galls, and it does not like some alkaline cleaners or wet concrete splash.
Coastal aluminium wants the right alloy and isolation from copper and from some stainless couples. The Alltrade family sold aluminium as a first language; this journal will not pretend to be that catalogue. It will say: do not casually mix swarf, and do not casually mix metals in a wet joint.
Aluminium sheet sizes and thicknesses are their own merchant lists. Do not assume a 2400 × 1200 stainless parent has an aluminium twin on the same rack, or that “16 gauge” means the same millimetre.
Contact and corrosion
Wet 316 against aluminium can bully the aluminium. The stainless stays pretty; the aluminium pits around the washer. Isolation — plastic washers, sleeved bolts, sealant where the designer allows it — is the grown-up detail in wet or coastal work.
Zinc against stainless can fuss in crevices. Carbon-steel dust on stainless rusts in place and photographs as a failed alloy. Copper-rich splash on aluminium is its own pitting story.
Protecting stainless is the handling page. Fasteners have their own alloy split; do not put the mixed tin on a coastal rail.
A mixed elevation — stainless splashback, galvanised stud, aluminium window — can be honest if the water path is designed. It is dishonest if the specification says “all metal to match.” They will not match. Specify each metal and the joint between them.
Fabrication habits that do not travel
Guillotine, laser and waterjet all cut these metals. The settings do not. Stainless work-hardens and wants the right blade and the right speed. Aluminium wants sharp tools and will grab a dull one. Galvanised fumes when you weld or grind it; that is a workplace problem, not a finish problem.
The historic stainless custom-cut counter published ±2 mm on sheared blanks and warned that a cut edge is not an extrusion. That honesty belongs on galvanised and aluminium blanks too. A laser or waterjet can tighten the window if you paid for it. An angle grinder on a balcony will not.
Folded stainless angle and channel are sheet products. Hot-rolled stainless sections are another family. Galvanised angle is usually a coated carbon section. Aluminium angle is often extruded. Do not substitute by drawing an L.
A short chooser
- Food face, hygiene, visible architecture: stainless, specified — alloy, finish, millimetres.
- Sacrificial outdoor structure on a budget, inland: galvanised, specified, edges thought about.
- Weight-sensitive cladding and windows: aluminium, specified by that trade.
- Coastal barrier a hand will touch: 316 stainless, not a zinc rail painted silver.
- Wet couple between stainless and aluminium: isolation, not hope.
If the quote is three metals and one postcode by the sea, make the couples explicit. Write the thickness in millimetres. Write the finish if it is stainless. Write the coating if it is zinc.
The sheet, plate and finishes hub is where stainless faces live. The custom-cut and sections hub is where blanks and folds live. This page is the doorway before you pick a family.