When you call a mobile welder, one of the first questions we ask is: what metal? It's not just about process — it changes the rate, the equipment we bring, and how the finished job holds up over time. Getting the metal right at the start avoids costly replacements later.
Here's how to think about the three materials we work with most.
The Quick Summary
| Property | Mild Steel | Stainless Steel | Aluminium |
|---|---|---|---|
| Our welding rate | $110/hr | $150/hr | $180/hr |
| Strength | High | Very high | Moderate–high |
| Rust resistance | Poor (needs coating) | Excellent | Excellent |
| Weight | Heavy | Heavy | Light (1/3 of steel) |
| Weld difficulty | Easy | Moderate | Hard |
| Typical finish | Paint/powder coat | Brushed/polished | Natural/anodised |
Mild Steel — The Workhorse
Mild steel is the default for most structural and general fabrication work. It's strong, widely available, easy to weld, and the cheapest of the three materials. If budget is a factor and the piece will be painted or powder-coated, mild steel is usually the right choice.
The catch: mild steel rusts. Without a protective coating — paint, powder coat, hot-dip galvanising — it will begin corroding within months in a Sydney climate, faster near the coast. Any chip, scratch, or weld area that hasn't been properly primed and painted will rust first. This isn't a problem if you maintain it; it's a disaster if you don't.
Use mild steel for:
- Gates, fencing, and frames that will be painted or powder-coated
- Structural connections, bracing, and pergola frames
- Trailers and ute trays (steel trays are heavier but tougher for heavy loads)
- Farm machinery repairs and agricultural equipment
- Interior stairs, handrails, and balustrades that won't see weather
- Any job where cost is the primary driver
Don't use mild steel for: anything in a coastal location, pool surrounds, or any outdoor application where the coating can't be maintained. The salt air in Sydney's Eastern Suburbs, Northern Beaches, and Sutherland Shire accelerates corrosion dramatically.
Stainless Steel — Built for Exposure
Stainless steel is steel with a high chromium content (typically 10–30%), which forms a passive oxide layer that prevents rust. Unlike mild steel, stainless doesn't need paint or powder coat to stay corrosion-resistant — the surface itself is the protection.
There are many grades, but two matter most for outdoor metalwork in Sydney:
- 304 stainless — the standard grade. Good corrosion resistance in most environments. Used for interior handrails, commercial kitchen equipment, and sheltered outdoor applications.
- 316 marine grade stainless — contains molybdenum, which dramatically improves resistance to salt water and chlorides. Essential for coastal properties, pool fencing, and anything within a few kilometres of the ocean.
We always recommend 316 for Sydney's coastal suburbs (Bondi, Manly, Cronulla, Mosman, and anywhere within 2–3km of the water). The cost difference between 304 and 316 is modest — the cost of replacing rusted 304 stainless in a salt-air environment is not.
Use stainless steel for:
- Pool fencing (AS 1926.1 compliance, salt-tolerant)
- Balustrades and handrails in coastal or exposed locations
- Commercial kitchen equipment — food-grade 316L grade
- Marine hardware, boat fittings, and waterfront infrastructure
- Architectural features where a polished finish is required
- Any exterior application that needs to look good without maintenance
Welding note: Stainless TIG welding requires clean technique and often back-purging with argon gas to prevent oxidation on the inside of the weld. Done correctly, the weld area maintains full corrosion resistance. Done poorly, you get discolouration and a weld that will corrode faster than the parent material. We take the time to do it right.
Aluminium — Light, Strong, and Corrosion-Proof
Aluminium is about one-third the weight of steel, naturally corrosion-resistant (it forms its own oxide layer), and the material of choice wherever weight matters. It's more expensive to weld — TIG welding aluminium is technically demanding and slower than MIG welding steel — but for the right applications it's worth every dollar.
Aluminium welding rates: $180/hr for welding, $230/hr for fabrication — roughly 65–75% more than the same job in mild steel. The premium reflects skill level, equipment cost, and preparation time. Aluminium must be completely clean before welding; any oil, oxide, or contamination causes porosity and weld failure.
Use aluminium for:
- Ute trays — lighter tray means more payload capacity; aluminium trays are the trade standard
- Boat hulls, marine pontoons, and aluminium dinghy repairs
- Aluminium trailers and caravan frames (much lighter than steel equivalents)
- Architectural aluminium — window frames, facades, louvres
- Coastal gates and balustrades where low maintenance matters
- Anywhere weight is critical — aviation, marine, motorsport
Don't use aluminium for: heavy structural applications requiring maximum strength per dollar. Steel is stronger for its cost. Also note that aluminium and steel cannot be welded together directly — mixing metals causes galvanic corrosion. If you're joining aluminium to steel, we use mechanical fasteners or a transition piece.
Which Metal for Common Sydney Jobs?
| Job | Recommended Metal | Why |
|---|---|---|
| Driveway gate (inner-city) | Mild steel, powder-coated | Cost-effective, durable when coated |
| Driveway gate (coastal) | 316 stainless or aluminium | Salt air corrodes mild steel within years |
| Pool fence | 316 stainless or aluminium | Chlorine + salt; must be corrosion-proof |
| Balustrade (inner city, sheltered) | Mild steel or 304 stainless | Both work; stainless easier to maintain |
| Balustrade (coastal / exposed) | 316 stainless | Only 316 handles long-term salt exposure |
| Ute tray | Aluminium | Weight saving = more payload |
| Trailer chassis | Mild steel | Strength, cost, and repairability |
| Boat hull repair | Aluminium | Match the parent material |
| Farm gate / rural fence | Mild steel | Tough, repairable, cost-effective |
| Structural beam connection | Mild steel or high-tensile | Strength and code compliance |
| Commercial kitchen bench | 304 or 316L stainless | Food-grade, easy to clean |
| Stair handrail (indoor) | Mild steel or 304 stainless | Aesthetic choice; both are fine indoors |
| Stair handrail (outdoor, coastal) | 316 stainless or aluminium | Weather and salt exposure |
Mixing Metals: What to Watch For
When two dissimilar metals are in contact with each other in a wet or salty environment, you get galvanic corrosion — the less noble metal corrodes faster than it would on its own. Common problem pairs in Sydney:
- Mild steel bolts through stainless posts — the steel bolts will rust faster than normal. Use stainless fasteners throughout any stainless installation.
- Aluminium next to steel — if they're touching in a wet environment, the aluminium will corrode. Use an insulating washer or sealant between the two materials.
- Galvanised steel near stainless — less of an issue, but worth considering for marine applications.
We flag these situations when we see them and advise on the right fasteners and isolation before starting the job.
The Bottom Line
For most structural and general-purpose welding in Sydney — mild steel. For anything exposed to water, salt, or the elements — stainless steel (316 near the coast). For weight-critical or marine applications — aluminium. When in doubt, call us and describe the job: we'll tell you what we'd use and why.
Want a quote for your specific job? Fill in our quote form or call us directly on 0455 797 227.