If your MIG welds look like Swiss cheese, you have porosity. Porosity is trapped gas bubbles in the weld metal, and it weakens the bead. The frustrating part is that porosity can come from a few different sources, and many people chase the wrong one. In Edmonton, outdoor wind and dirty winter steel are two of the biggest culprits.

This guide is a practical checklist to diagnose porosity fast and fix it the right way.

Start with the pattern

Porosity can show up in different ways:

  • Porosity in every bead: usually shielding gas coverage, leaks, or contamination.
  • Porosity only at starts and stops: technique, gas preflow, or dirty tack areas.
  • Random porosity bursts: wind gusts, intermittent leaks, or inconsistent surface contamination.

Cause #1: wind and poor shielding gas coverage

MIG needs shielding gas to protect the puddle. Outdoors, wind can blow that gas away. It does not take a gale. Even light wind in an open driveway in Sherwood Park can cause porosity.

  • Fix: set up a windbreak. Even a simple screen makes a big difference.
  • Fix: keep the nozzle close and maintain a steady travel angle.
  • Fix: avoid excessive stick-out that pushes the arc away from the gas envelope.

Cause #2: gas leaks and bad connections

If you have porosity indoors with no wind, start checking the gas path.

  • Regulator and hose: look for cracks, loose fittings, and damaged O-rings.
  • Gun connection: check the torch connection to the feeder.
  • Diffuser and nozzle: spatter buildup can block flow or create turbulence.

A quick trick is to listen for a hiss at connections and check that your flow rate stays steady when you trigger the gun.

Cause #3: contaminated base metal

Dirty steel is a porosity factory. Common contaminants in Edmonton include:

  • Paint and primer
  • Rust and mill scale
  • Oil and grease (especially on equipment)
  • Road salt and slush residue

Fix: grind to bright metal, wider than you think. If you only clean a narrow strip, contamination right next to the joint can still get sucked into the puddle as you weld.

Cause #4: moisture

Moisture can come from wet steel, condensation, or damp wire. In winter, condensation is sneaky. Bring cold steel into a warmer garage and moisture forms on the surface. You might not even see it, but the arc will.

  • Fix: dry the joint. Gentle preheat can drive off moisture.
  • Fix: store wire spools dry and covered, especially in a mobile truck.

Cause #5: wrong technique and stick-out

Technique can cause porosity even with good gas and clean steel:

  • Too much stick-out: reduces gas coverage at the puddle.
  • Bad angle: pushing or pulling too aggressively can expose the puddle.
  • Travel too fast: can create turbulence and incomplete shielding.

Keep a consistent stick-out, keep the nozzle close, and maintain a steady angle.

Cause #6: gas type mismatch

Shielding gas matters. The correct mix depends on the wire and material. If the gas type is wrong, you can get unstable arc and more defects. If you are unsure what gas you are running, check the cylinder label and your wire specs.

A fast diagnostic sequence

If you want a quick path to the answer, run this order:

  • 1) Wind check: if you are outdoors, build a windbreak.
  • 2) Clean check: grind to bright metal and wipe.
  • 3) Gas check: inspect connections, nozzle, diffuser, and flow.
  • 4) Moisture check: dry the joint, dry the wire environment.
  • 5) Technique check: shorten stick-out, steady angle, steady travel.

When porosity means you should stop and redo

Small surface pores in a non-critical spot might be acceptable on some jobs, but if the weld is structural, load-bearing, or safety-related (like a trailer hitch or handrail), porosity is not something to ignore. Grinding out and re-welding is usually the right move.

Need a clean weld in tough conditions?

Mobile welding in Edmonton often means wind, cold steel, and dirty repairs. YEGWELD is set up for real-world conditions and focuses on prep and process choice to avoid defects like porosity.

Call: 780-233-8285 or contact us here to send photos and get a quote.

This article is for informational purposes only and may contain inaccuracies. Always consult a certified welding professional before starting any project.

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