Shielding gas keeps oxygen and nitrogen away from your molten weld pool. Get it right and your welds are clean and strong; get it wrong and you'll fight porosity, spatter and weak joints. Here's which gas goes with which job.
What the gas actually does
The instant metal melts, the air around it wants to react with it — causing porosity and weak welds. Shielding gas blankets the pool to keep that air out. Different gases also change how the arc behaves, how much spatter you get and how deeply the weld penetrates, so the "right" gas is the one matched to your process and material.
MIG on mild steel
- Argon/CO₂ mix (commonly 80/20): the everyday favourite for steel MIG — a stable, smooth arc with good penetration and modest spatter. The right call for most fabrication.
- Pure CO₂: cheaper and deeper-penetrating, but a harsher arc with more spatter. Fine for heavier, less cosmetic work.
MIG on stainless steel
Stainless wants a tri-mix (typically argon with a little CO₂ and a trace of helium or oxygen) to keep the weld clean and corrosion-resistant without too much heat. If you only weld stainless occasionally, ask us about the most economical option for your volume.
MIG on aluminium
Aluminium MIG needs pure argon (helium is sometimes added on thicker sections for more heat). Don't use a CO₂-containing mix on aluminium. A spool gun or a good liner setup helps the soft wire feed cleanly.
TIG — almost always pure argon
TIG welding uses pure argon across steel, stainless and aluminium for that clean, controllable arc. Helium blends exist for more heat on thick aluminium, but for the vast majority of TIG work, argon is the answer.
Gasless wire needs no bottle. Flux-cored (gasless) MIG wire shields itself, which is why it's the choice for windy and outdoor work where a shielding gas would simply blow away. No cylinder, no regulator — just the right wire.
Flow rate and a few practical points
- Set a sensible flow rate — too little and air gets in, too much and you get turbulence that pulls air in anyway. Indoors, a steady moderate flow is plenty; wind needs more or a move to gasless.
- Check for leaks at the regulator and hose — a slow leak wastes expensive gas and ruins welds.
- Store cylinders upright and secured, valves closed when not in use (more in our storage guide).
A note on supply: for safety, compressed-gas cylinders are counter-collection or local delivery only — they can't travel on a national courier. Pop in or call and we'll sort the right gas and cylinder for you.