FCAW is the American Welding Society abbreviation for Flux-Cored Arc Welding, usually shortened to flux-core. It was developed in the 1950s to combine the productivity of wire feeding with the self-shielding of a stick electrode. If you bought an inexpensive 120 V “gasless MIG” welder, you own an FCAW machine. If you have watched ironworkers running fat, fast beads on a steel beam in the open air, that was FCAW too.
Quick Answer
FCAW stands for Flux-Cored Arc Welding. It uses the same wire-feed gun as MIG, but the wire is a hollow tube filled with flux. Self-shielded flux-core (FCAW-S) needs no gas cylinder and works outdoors on rusty steel, which is why gasless 120 V welders use it. Gas-shielded flux-core (FCAW-G, “dual shield”) adds CO2 or argon-CO2 and is the high-deposition choice for thick structural steel.
Key Takeaways
- FCAW = flux-core welding. Two versions: self-shielded (no gas) and gas-shielded (dual shield).
- Think of it as stick welding with a continuous wire: flux does the shielding, slag must be chipped.
- Most self-shielded wires such as E71T-11 and E71T-GS run on DCEN, the opposite of MIG.
- Best for outdoor work, dirty steel, and plate 1/8″ and thicker. Harder on thin sheet than MIG.
- Highest deposition rate of the four common manual processes when run with gas.
What Does FCAW Stand For?
- Flux-Cored: the electrode is a tubular wire whose hollow core carries flux powder, deoxidizers and alloying elements.
- Arc: an electric arc between the wire and the workpiece supplies the heat.
- Welding: wire and base metal fuse together.
The letters are completed with a suffix: FCAW-S is self-shielded (the flux alone protects the puddle) and FCAW-G is gas-shielded (flux plus an external gas). The two behave differently enough that they are often treated as separate processes. Both sit next to SMAW, GMAW and GTAW in our welding acronyms comparison.
How FCAW Welding Works
The machine is a constant-voltage power source with a wire feeder, the same hardware as MIG. The difference is inside the wire. As the arc melts the tubular wire, the flux in the core vaporizes into shielding gas and forms a slag blanket over the bead, exactly as a stick rod coating does. On FCAW-S that is the only shielding, so the puddle survives wind that would ruin a MIG weld. On FCAW-G the gas from the nozzle does most of the shielding while the flux adds deoxidizers, arc stabilizers and a slag that supports the puddle out of position.
Because the current flows through a thin metal sheath rather than a solid wire, current density is high and penetration is deep for a given wire size. Stick-out is longer than MIG, typically 3/4″ to 1″ on self-shielded wire, and a drag (pull) technique is used so the slag stays behind the arc.
Polarity
This catches many people. Solid MIG wire runs DCEP. Most self-shielded flux-core wires, including E71T-11 and E71T-GS, run DCEN, which means swapping the leads inside the machine. Gas-shielded wires such as E71T-1 generally run DCEP. Always read the spool label; running the wrong polarity gives a ragged arc, heavy spatter and poor penetration. Details are in our welding polarity guide.
FCAW-S vs FCAW-G
| FCAW-S (self-shielded, gasless) | FCAW-G (gas-shielded, dual shield) | |
|---|---|---|
| Shielding | Flux only | Flux + CO2 or 75/25 Ar/CO2 |
| Common wires | E71T-11, E71T-GS, E71T-8 | E71T-1, E71T-9, E71T-12 |
| Polarity | Usually DCEN | Usually DCEP |
| Outdoor use | Excellent | Poor (gas blows away) |
| Spatter and smoke | Heavy | Moderate |
| Weld quality | Good; some wires limited to single pass or thin plate | Excellent; code-quality structural welds |
| Typical user | Home 120 V welders, field repair, farm | Shipyards, structural fab, heavy equipment |
Reading Flux-Core Wire Numbers
Take E71T-11 as the example:
- E: electrode.
- 7: minimum tensile strength of 70,000 psi.
- 1: all-position (a 0 here means flat and horizontal only).
- T: tubular wire.
- -11: usability designator. 11 is a general-purpose self-shielded wire; GS is single-pass self-shielded; 1 is a gas-shielded rutile wire; 8 is a self-shielded wire rated for structural multi-pass work.
Our flux-cored wire types and uses article lists the common ones, and the flux-core amperage chart gives starting settings by thickness.
Advantages of FCAW
- Works outdoors and in drafts (self-shielded).
- Tolerates rust, mill scale and light paint far better than MIG.
- Deep penetration and the highest deposition rate of the manual processes with gas.
- No cylinder needed for FCAW-S, so a 120 V machine and a spool is a complete setup.
- All-position welding on thick plate with the right wire, with a slag that holds the puddle up.
Limitations of FCAW
- Slag and spatter must be removed after every pass.
- Smoke. Self-shielded wire produces heavy fumes; ventilation or a fume extractor matters.
- Poor on thin sheet. Below about 18 gauge the arc is too hot and the slag too heavy; use MIG with 0.023″ solid wire instead. Our guide on flux-core on thin sheet metal shows what is possible.
- Wire cost is higher per pound than solid wire.
- Not for aluminum; there is no practical aluminum flux-core wire.
What FCAW Is Used For
Structural steel, bridges, shipbuilding and heavy equipment (FCAW-G); fencing, trailers, farm repair, outdoor fabrication and most 120 V home welding (FCAW-S). It is the go-to when the steel is thick, dirty or outside, and the finished look matters less than fusion.
FCAW vs GMAW (Flux-Core vs MIG)
Same machine, different wire. MIG is cleaner, better on thin metal and indoor work, and makes prettier beads. Flux-core wins outdoors, on rusty plate and on anything 1/4″ and up with a small machine. A 120 V welder without a gas cylinder can only run flux-core. If you are unsure which you need, does flux-core welding require gas walks through it.
Common FCAW Problems and Fixes
- Worm tracks (lines of porosity on the bead): voltage too high or stick-out too short on self-shielded wire. Lower voltage, lengthen stick-out to about 3/4″.
- Heavy spatter and a sputtering arc: wrong polarity. Switch to DCEN for self-shielded wire.
- Slag trapped in the weld: pushing instead of dragging, or not cleaning between passes.
- Burn-through on sheet: wire too large or too hot; drop to 0.030″ wire, lowest setting, and stitch weld.
- Wire feed stalls: flux-core wire is softer than solid; use knurled drive rolls and lighter tension.
Frequently Asked Questions
Is FCAW the same as MIG?
No. They share the wire-feed machine, but MIG (GMAW) uses solid wire plus gas, while FCAW uses flux-filled tubular wire. Shops often lump them together as “wire welding.”
Does FCAW need gas?
Self-shielded FCAW-S does not. Gas-shielded FCAW-G does, usually 100% CO2 or 75/25 argon-CO2.
What polarity does flux-core use?
Most self-shielded wires use DCEN (electrode negative). Most gas-shielded wires use DCEP. Check the spool.
Can you weld thin metal with flux-core?
Down to about 18 to 20 gauge with 0.030″ wire, low settings and short stitches. Thinner than that, MIG or TIG is the better tool.
Is flux-core as strong as MIG?
Yes. E71T wire deposits 70,000 psi weld metal, the same as ER70S-6 MIG wire, and flux-core usually penetrates deeper on thick plate.
Conclusion
FCAW gives you stick-welding toughness with wire-feed speed. Self-shielded flux-core is the reason a $200 welder can fix a trailer in the driveway, and gas-shielded flux-core is why structural crews can lay down pounds of weld metal an hour. Learn the polarity rule, drag the gun, chip the slag, and it will handle thick, dirty and outdoor steel that MIG cannot. For the full lineup of processes, read SMAW vs GMAW vs FCAW vs GTAW.
Sources
- AWS A5.20/A5.20M, Specification for Carbon Steel Electrodes for Flux Cored Arc Welding
- AWS A3.0M/A3.0, Standard Welding Terms and Definitions
- Lincoln Electric, Innershield Welding Guide
- Hobart Brothers, Flux-Cored Wire Selection Guide
