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)
- 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 2026-06-05 / 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.
