Why Your MIG Weld Has Porosity (and How to Fix It Fast)

Adam — Wed, 29 Apr 2026 18:04:14 +0000

Porosity in MIG welding shows up as pinholes or small voids in the weld bead. It weakens the weld and usually points to shielding gas failure or contamination. This guide breaks down the exact causes and the fastest way to fix it using proper setup and wire selection.

Key Takeaways

Porosity is caused by poor shielding gas coverage or contamination
Dirty metal and bad wire are the most common causes
Gas flow, nozzle condition, and wire choice fix most issues
ER70S-6 wire helps reduce porosity on less clean steel

What Causes MIG Weld Porosity

Porosity occurs when atmospheric gases get trapped in the weld pool as it solidifies. In MIG welding, shielding gas is supposed to prevent this. When coverage fails, defects form.

Low shielding gas flow
Wind or airflow disrupting gas
Dirty or oily metal
Rusty or contaminated wire
Improper stickout or angle
Clogged nozzle or diffuser

How to Fix MIG Porosity

Set gas flow to 20–30 CFH (verify for your setup)
Keep stickout around 3/8”–1/2”
Clean metal to bare steel
Check for gas leaks
Replace worn nozzle or diffuser
Switch to ER70S-6 wire if needed

Recommended Wire for Reducing Porosity

Hobart ER70S-6 MIG Welding Wire (.030”)

Type: Solid MIG wire

Diameter: .030”

Material: Mild steel

Deoxidizers: Higher than ER70S-3

Specs: Unknown (Verify)

Hobart H305406-R22 10-Pound ER70S-6 Carbon-Steel Solid Welding Wire, 0.030-Inch

Carbon-steel sound, porosity-free welds with powerful deoxidizers for your work with shielding gases.
Great for construction work, farm implement fabrication, shaft buildup, tanks, truck bodies and general shop applications with poor fit-up or rusty, oily plates.
10-Pound spool
Country of Origin: Made in China

Last update on 2026-05-02 / Affiliate links / Images from Amazon Product Advertising API

ER70S-6 wire is more forgiving on dirty steel and helps reduce porosity compared to ER70S-3.

Gas Flow Setup

Typical: 20–30 CFH (verify)
Too low = poor coverage
Too high = turbulence
Avoid drafts when welding

Wire Comparison

Wire	Key Difference	Best Use
ER70S-6	More deoxidizers	Dirty steel
ER70S-3	Cleaner arc	Clean material

Safety Notes

Use ANSI Z87.1 compliant eye protection and proper PPE. Ensure ventilation and follow AWS welding safety guidelines.

FAQ

Q: Can too much gas cause porosity?
A: Yes. It can create turbulence and pull in air.

Q: Does wire matter?
A: Yes. ER70S-6 is more forgiving on dirty steel.

Next Step

Check your gas flow and nozzle first. If needed, switch to ER70S-6 wire and clean your material before welding.

welding porosity – Weld Support Parts Blog