Most flux-cored welding faults trace back to machine setup, polarity or material condition. Get the polarity right for your wire type, remove slag completely between passes, and most defects — porosity, worm tracks and spatter — disappear. This page covers correct polarity, why slag removal matters, and how to fix the most common flux-cored welding problems.
What polarity should flux-cored wire use?
The correct polarity depends on the wire type. Most gas-shielded flux-cored wires use DC Electrode Positive (DCEP), while many self-shielded wires require DC Electrode Negative (DCEN). Always follow the manufacturer’s recommendations, as using the wrong polarity will affect arc stability and weld quality.
Does flux-cored welding produce slag?
Yes. Flux-cored welding produces a protective slag that must be removed after welding. Proper slag removal allows inspection of the weld and prevents defects when depositing additional weld passes.
Why is slag removal important?
Removing slag prevents slag inclusions, improves weld appearance and allows proper inspection of the completed weld. Always remove slag completely before applying additional weld passes — trapped slag between passes is a common cause of weld defects.
What causes porosity in flux-cored welding?
Porosity is commonly caused by contaminated material, moisture, incorrect shielding gas, excessive stick-out or poor welding technique. Using clean materials and following the wire manufacturer’s recommendations helps prevent porosity.
What causes worm tracks in flux-cored welding?
Worm tracks are surface marks caused by gas escaping through the solidifying weld. They may result from excessive voltage, incorrect travel speed or poor welding technique. Correct machine settings usually eliminate the problem.
What causes excessive spatter with flux-cored wire?
Excessive spatter may result from incorrect voltage, wire feed speed, polarity or shielding gas selection. Proper machine setup and quality welding consumables help produce a smoother, more stable arc.
Quick troubleshooting summary
| Problem | Common causes |
|---|---|
| Porosity | Contaminated material, moisture, incorrect shielding gas, excessive stick-out, poor technique |
| Worm tracks | Excessive voltage, incorrect travel speed, poor technique |
| Excessive spatter | Incorrect voltage, wire feed speed, polarity or shielding gas selection |
| Slag inclusions | Incomplete slag removal between passes |
For wider fault-finding across all welding processes, see the welding defects and troubleshooting hub.
Related pages
- Flux-Cored Welding hub — the complete guide to FCAW.
- How Flux-Cored Welding Works — the process and the slag it forms.
- Gas-Shielded vs Self-Shielded Flux-Cored Wire — polarity differs by wire family.
- Welding Defects & Troubleshooting hub — faults across all processes.