Troubleshooting guide › Process troubleshooting › Flux-cored (FCAW) welding problems
Flux-cored wire runs on the same MIG machine as solid wire, but it is not solid wire with a different label. It has its own polarity, its own stick-out, a slag to remove and, for self-shielded types, no gas at all. Most FCAW trouble comes from running it with solid-wire habits. This page separates the two wire families and lists the faults that belong to each.
Reviewed by the Cruxweld technical team, October 2026. Settings are starting points to confirm on a test piece; acceptance is decided by the code or drawing the job is built to. Checks marked “call” are for our technical team.
| Gas-shielded flux-cored (E71T-1, E71T-5 types) | Self-shielded flux-cored (E71T-11, E71T-GS, E71T-8 types) | |
|---|---|---|
| Shielding | CO2 or Ar-CO2 from the torch, 18-22 L/min | None: the flux makes its own; a gas nozzle is removed or replaced by a slip-on guide |
| Polarity | DC electrode positive (DC+) for nearly all; confirm on the data sheet | DC electrode negative (DC-) for most; confirm on the data sheet |
| Stick-out | 15-25 mm | 20-40 mm, longer than solid wire; too short gives porosity because the flux has no time to react |
| Where it fits | Shop fabrication, thick plate, high deposition, position welding with the T-1 types | Site and outdoor work, wind, repair, where gas is impractical |
| Bead | Smooth, slag peels easily, low spatter on Ar-CO2 | More spatter and smoke; slag must be removed between passes |
| Weld metal | Good toughness with the right class | Some GS types are single-pass only; check before multi-pass structural work |
Metal-cored wire is a third type: a tubular wire filled with metal powder, no slag, run like solid wire on Ar-CO2 at DC+, mostly for high-speed flat and horizontal fillets.
A self-shielded wire run on DC+ (or a gas-shielded wire on DC-) gives a violent arc, heavy spatter, porosity and a bead that will not wet.
Porosity and worm tracks along the whole bead.
The flux does not reach reaction temperature before the arc; porosity and worm tracks (long, straight gas tracks on the surface), especially on self-shielded wire.
Too high: long arc, flat bead, slag trapped at the toes, worm tracks. Too low: convex ropey bead, slag trapped under the bead, spatter.
Slag inclusion in the next pass, especially in the toe corners of a fillet.
Molten slag runs ahead of the pool and is welded over.
Flux-cored wire absorbs moisture through the seam of the tube; porosity and worm tracks after a monsoon week in the open.
Tubular wire crushes under V-groove rolls or too much pressure, then jams in the liner; flakes of flux block the liner.
Flux-cored wire runs hotter and longer stick-out; a worn tip wanders the arc.
Self-shielded wire tolerates some rust and mill scale; it does not tolerate paint, oil or galvanising.
| Gas-shielded E71T-1, flat fillet | 200-280 A, 25-30 V, CO2 18-20 L/min, DC+, stick-out 15-20 mm |
| Gas-shielded E71T-1, vertical-up | 160-200 A, 23-26 V, stringer or slight weave |
| Self-shielded E71T-11, 6 mm plate | 150-200 A, 17-21 V, DC-, stick-out 20-30 mm, no gas |
| Self-shielded E71T-GS, thin sheet | 0.9 mm wire, 80-130 A, 15-18 V, DC-, single pass only |
| Metal-cored 1.2 mm | 220-300 A, 26-30 V, Ar-CO2, DC+, stick-out 15-20 mm |
| Drive rolls | Knurled V for the wire size; light pressure |
Starting points only. The wire maker’s data sheet overrides this table; confirm on a test piece.
Long, shallow, straight gas tracks on the surface of a flux-cored bead, like a worm has crawled along it. Gas from the flux escaped while the surface was freezing. Causes: stick-out too short, voltage too high, damp wire, wrong polarity, or no gas on a gas-shielded wire.
Yes: knurled rolls, the polarity the wire needs, and the gas the wire needs (or none). The voltage will sit 1-3 V higher than solid wire for the same current.
Self-shielded wire handles wind that would ruin a gas-shielded weld, but the long stick-out and a steady hand still matter. Above a strong breeze, screen the joint anyway.
Any Cruxweld MIG machine runs flux-cored wire if it has knurled drive rolls for the wire size and output terminals you can swap for polarity. For 1.6 mm flux-cored wire at 350 A and above, a 4-roll feeder and a water-cooled torch keep the feed steady and the torch cool. Follow the wire maker’s data sheet for polarity, gas and voltage; it overrides any generic table.
Send a photo of the weld or cut, your machine model, consumable and plate thickness. Our technical team replies on WhatsApp with the likely causes and the next checks to make.
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